diagnosing animal diseases

Animal Diseases & Zoonoses: Diagnosis, Treatment And Control

If there is one thing that concerns a farmer most, it is animal health. Healthy cows produce optimally and justify the hefty investment associated with dairy farming. Diagnosing animal diseases becomes a key component of farm management.

In this article, we are going to look at some of the very common diseases at the farm, how to diagnose and manage them for better performance at the farm.

First, we should define some of the important terms we are going to be using throughout this post.

Definition of important terms

Zoonotic disease: – disease that can be transmitted between man and animal.

Food-borne disease: – disease that is transmitted through food. It is a public health concern.

Health: – a state of freedom from any disease or abnormality.

Disease: – Any deviation from a healthy condition. Usually manifested as an inability to perform physiological function at normal levels even when nutritional and environmental requirements are adequate.

Diagnosing Animal Diseases: How to Do it Right

Caveat

Always consult a professional if you are unsure of what you are doing.

When diagnosing a disease, you can do it on an individual animal or collectively on a herd/flock.

There are several ways this can be done. We will look at three approaches that are commonly used.

  • General examination/parameters
  • Specific examination/parameters
  • Clinical examination

General parameters

Here, you check for the general appearance of the animal. For instance;

  • Demeanor – check if the animal is either dull or bright.
  • Posture – check the animal’s recumbency (i.e. any sign of the animal assuming an abnormal posture). Recumbency can be either sternal or lateral. Check the backbone curvature (any abnormality could signal a health problem and its magnitude).
  • Gait/walking style – the animal can exhibit an unsteady gait due to problems with the nervous system in the spinal cord. The animal could also exhibit a circular gait due to a problem with the central nervous system in the brain. If the animal has a problem with the skeletal system, you will see it limping.
  • Body condition/conformity – you could observe obesity or emaciation. There could also be extreme cases of emaciation (cachectic) in which the animals are so thin that they cannot even eat. You can also check the body coat (which can be smooth and shiny when the animal is healthy or rough and dry when the animal is sick).
  • Skin changes – sick animals tend to have soiled bodies with faeces, blood, or pus. They could also lose hair (alopecia) and be infested with external parasites such as ticks.
  • General behavior – the animal’s voice could change and become coarse. The animal could keep bellowing, which could indicate infection with rabies. You may also notice that an animal that was very active becomes very inactive suddenly.

Specific parameters

Check close parameters that usually have immediate impact when the animal is unwell. For instance;

  • Appetite – this is the first aspect to be affected when the animal is unwell. The animal can exhibit capricious appetite that goes over the normal level, reduced below the normal level or even anorexic. You may also notice that the animal has problem chewing or swallowing the feed. In some cases, the animal could suddenly develop pica (craves soil/uncommon feed). This can indicate deficiency for a particular mineral in their system.
  • Defaecation – the animal could be constipated and produce hard faeces. It could also diarrhea or develop dysentry (produce diarrhea with blood). Aside from these two symptoms, you could also observe the animal straining during defaecation. It could be so strenuous that the animal develops rectal prolapse. However, do not overlook the fact that the prolapse could be due to paralysis.
  • Micturition (urination) – the animal could have difficulty urinating due to urethral stones. It could also be painful as a result of inflammation. In other cases, you may notice the animal has urine incontinency (constant dripping of urine), which may be due to paralysis of the bladder or the sphincter muscles that fail to close properly.
  • Mucus membrane – you may notice that the membranes have deviated from their normal bright pink colour. Paleness could be a signal for anaemia. You may also observe congestion (the mebranes become deep red, which indicates high vascularization. A yellowish mucus membrane could indicate jaundice, which indicates presence of liver problems.
  • Temperature – Any deviation from normal (i.e. either fever or hypothermia) could indicate a problem. For instance, if an animal is poisoned, you will notice hypothermia. Drop in temperature could also be as a result of diarrhea.
  • Pulse rate – it could be fast or slow depending on the health of the animal and other external conditions. It could also be weak or strong based on similar reasons. For instance, a healthy cow should have between 60 and 80 heartbeats per minute while a healthy calf should have between 100 and 120 heartbeats per minute.
  • Respiration – observe how the animal breathes in and out. Check the ribcage movements. You could observe that the animal has difficulty breathing (dyspnea), painful breathing, or is very weak. For this exercise, you can also use a stethoscope to auscultate the rates more accurately. A healthy cow should take between 10 and 30 breaths per minute. A horse on the other hand takes just between 80 and 10 breaths per minute.

Clinical examination

Clinical examinations are more advanced hence require expertise. Before you start the process, ensure that you retrain the animal properly to avoid injuries. You should also have the personal protective gear suitable for the job.

The aspects of interest in clinical examination include:

a) History of the animal’s health

History is critical because it gives a clue as to what disease is suspected. It should be precise and accurate, preferably recorded.

What to consider when gathering an animal’s health history:

  • Be diplomatic when asking questions
  • Use non-professional language because you are dealing with a farmer
  • Test for time-based information
  • Avoid reading your questions, the farmer will tell you are not qualified to handle his animal and refuse to respond correctly. Read questions at the end when you have gathered enough information and you just need emphasis.
  • Take history of the patient such as age, sex, etc.
  • Record history of the disease sequentially i.e. how the symptoms set in
  • Record management programs for feeds, cleaning, production, health, etc.

b) Environmental examination

Both internal and external environmental factors have a significant impact on the health of the animal.

Outdoor environmental factors include topography, soil type (affects mineral balance) stocking rate (may induce cannibalism), type of pastures (some plants may cause poisoning), etc.

Internal environmental factors include the type of housing, level of sanitation, lighting, ventilation, etc.

c) Examining the individual animal

Conduct a general inspection of the general appearance of the animal before you know where to settle on.

Do a detailed close examination of the animal while making sure not to upset the animal in any way.

Unsettled animal may not reveal the true conditions because the pulse (or even the body temperature) will increase.

Approaches Employed In Examining a Sick Animal

We have seen the many ways you can use to conduct animal health diagnosis. We will now see how to approach a sick animal for examination.

a) Body regions

i) Head region

The head is a very important region in an animal. You can use it to check for the animal’s demeanor and facial expression (fright or excitation).

You can also check the head for symmetry and configuration of the mandibles. Use this to check how the animal carries its head.

In the head, you can check if the animal has protruded eyes, which can indicate a problem with the nervous system. Check for spasms, excessive blinking, lacrimation (tear production), etc.

Check the nostrils for excessive discharge of mucus or excessive dilation.

Observe the mucus membranes in the mouth for colour change, erosion of the gums, and salivation.

ii) Neck region

Check the jugular vein if it is glandular or smooth. Observe its pulse and check if there is any sign of fluid accumulation, which may show a problem with the circulatory system.

Check the size and variations of the lymph nodes. Irregular variation could indicate that the animal is suffering from goiter.

iii) Thorax

Check the ribcage and observe the rate, strength, and intensity of respiration.

iv) Abdomen

Check the size, alignment/symmetry, and any distention in the abdominal region. Such protrusions may indicate presence of gas/fluid accumulation or tumor.

v) Udder

You should give the udder special attention. Check for symmetry, irregular nodules/swellings, wounds, and dirt. Strip the teat and check the secretions for mastitis.

vi) External genitalia

Check the vulva and the mucus membranes for any deviation in color. Palpate these regions (including the testicles) for any irregular swellings/tumors.

Check discharges from these regions for any abnormality.

vii) Limbs

Check the animal’s posture and gait. Check for swellings or wounds on the skin.

b) Body systems

i) Respiratory system

Check the nose and the ribcage for any abnormality we have discussed in prior.

ii) Gastro-intestinal Tract (GIT)

Start from the mouth and go through the animal in the abdomen, the stomachs, the rectum and the external genitalia.

iii) Circulatory system

Here, check the mucus membranes for their colour, the jugular vein for pulse, and the lateral sternum on the left side of the animal to feel the heartbeat.

iv) Skin

Skin is the largest organ of the body and the barrier between internal organs and the external environment. Check for wounds, swellings, pests, alopecia, etc.

v) Skeletal system

Check the animal’s conformation and posture. Check for broken limbs as well. Ensure the hooves are well trimmed.

How to Conduct Tentative Diagnosis in an Animal

Tentative diagnosis is one that will lead you to identifying the specific problem with your animal. After carrying out the general diagnoses we have covered so far, you can complement them with the following techniques to isolate the case:

a) Palpation

Involves direct feeling with the hands/fingers for the size of a swelling, consistency (whether soft or hard), and sensitivity (to pain and temperature).

b) Percussion

Strike the body surface to set the deep parts into vibration. These vibrations will emit audible sound, which you can use to tell if the animal is sick or not.

c) Ballottement (tactile percussion)

This technique combines both palpation and percussion. It is a useful technique for diagnosing pregnancy in small animals.

d) Auscultation

Involves listening to sounds produced by the organs. You can listen directly by placing your ear above the surface or by use of a stethoscope.

e) Auscultation and percussion

Set the organs in motion and listen to the sounds they produce.

Parameters used for tentative diagnosis

i) Temperature

The health of the animal affects its temperature. Temperature could be normal, high, or low. These deviations could be defines as follows:

  1. Hypothermia – lower than the normal temperature
  2. Hyperthermia – higher than the normal temperature
  3. Pyrexia/fever – high temperature mixed with an infection
  4. Septicaemia – hyperthermia with infectious organisms in the blood
  5. Toxaemia – high temperature with infectious organisms producing toxins in the blood

ii) Pulse

Determines the heartbeat rate of the animal. For large animals, you can detect this at the mid-coccidial artery (in the tail end). Use fumeral artery for small animals. You may notice the following from this examination:

Tachycardia – marked increase in pulse rate e.g. during septicaemia or toxaemia. It could also happen during circulatory failure, extreme  pain or excitement.

Bradycardia – marked decrease in pulse rate, which occurs mainly on space-occupying lesions in the brain or diaphragm.

iii) Rectal palpation

Useful for pregnancy diagnosis and deformities in organs.

iv) Abdominal auscultation

You can listen to abdominal movements in animals with digestive problems.

Confirmatory Diagnosis (Laboratory Tests)

Take samples for lab examination. Ensure you follow the good sampling practices.

The samples include:

1) Blood

Use a dry sterile needle and syringe to collect the blood sample. If you are looking for large samples, use the jugular vein to draw the sample.

You can also use coccidial veins or the veins on the tip of the ears to draw samples.

Types of blood samples used for lab analysis

  1. EDTA – contains an anti-coagulant to prevent clotting
  2. Whole blood – encourages clotting and the blood separates into serum and solids. The serum is useful in identifying the type of infection.

2) Urine

Use a clean and sterile universal bottle to collect the sample. You can use the urine for urinalysis, sugar content, and culture for microbiological analysis.

3) Faeces

You can use the faeces for identifying worm infections and for cultural isolation to identify bacterial infections.

4) Lymph node

Pick a prescapular or parotid lymph node biopsy in a clean dry bottle. You can use the sample for smears and bacterial isolation.

5) Skin scrapping

Scape deep into the skin using a clean scalpel and collect in a clean container for ecto-parasite and fungal analysis.

6) Secretions

Could be milk or pus. Collect in a clean sampling bottle for chemical or biological analysis.

7) Tissue sections

Take a section of the organ to check for abnormalities like tumors.

8) Others

You can also collect samples from the feeds, organs, chemicals, plants, content of the stomach, etc.

How Diseases Manifest in Animals

  • Change in animal demeanor
  • Loss of appetite
  • Drop in production
  • Fever
  • Anaemia (paleness of the mucus membrane)
  • Intolerance to exercise

Specific manifestations of a disease will lead to differential diagnosis to eliminate diseases showing different pathognomonic signs (i.e. signs that cannot be mistaken for any other disease).

Causes of Animal Diseases in a Dairy Herd

Basically, there are three causes of diseases, namely:

       i. Environmental factors

They are either extrinsic or intrinsic factors. They include feeding, housing, hygiene, milking techniques, stress, as well as hereditary factors.

     ii.  Physical causes

These result from physical injuries, chemicals and irradiation.

   iii.  Microorganisms

Primary invaders of the body attacks the host and causes diseases. Secondary invaders cause opportunistic infections while a viral infection becomes a predisposing factor for other opportunistic infections.

Inapparent infection happens when the cause of the disease is not manifested in the body. It is also known as sub-clinical or latent infection and the host is a carrier.

There are different types of disease carriers, e.g.

  1. Incubatory carrier – the host carries the infectious organisms, which are multiplying actively to reach an attacking threshold.
  2. Convalescent carrier – these carriers host the disease-causing organism between the disappearance of the disease signs and complete disappearance of the disease agent.
  3. True carrier – presence of a balance relationship between the agent of the disease and the host throughout their course. They become sources of infections such as typhoid fever.

Transmission of Diseases in a Dairy Herd

Involves movement of disease causing microorganism from one (sick) animal to the next.

Methods of disease transmission

i) Through contact

Diseases that spread through contact are contagious. They can spread through direct contact (e.g. anthrax) or indirect contact when an infectious material gets on an auxiliary body such as feeds or posts then another animal picks it up (e.g. Salmonellosis and Colibacillosis).

ii) Vector transmission

Mechanical vector transmission – vector parasites like flies and ticks carry the disease from one animal to the other.

Biological vector transmission– some part of the disease-causing microorganism’s life cycle is completed in the vector.

Intermediate hosts – the vector parasite needs another host to complete the transmission e.g. Fascioliasis caused by liver flukes needs snails as an intermediate host.

iii) Mechanical transmission

Equipment with sharp or piercing edges used for vaccination and intravenous transfusion. Anthrax spreads through this method quite easily.

Vectors may also transmit diseases mechanically and is very common with viral infections.

iv) Experimental transmission

Usually done for academic and research purposes. The inoculum form one animal is introduced into the other animal to check its effects.

Routes of Transmission

i) Ingestion

The animal ingests the host through the mouth while feeding or drinking.

ii) Inhalation

The animal inhales the airborne vectors. This is common in anthrax, spore producing bacteria, and fungi.

iii) Contact (mucus membrane)

Infectious materials get into the animal through contact with the mucus membrane. Viruses are very notorious for this.

iv) Inoculation

An infectious agent is introduced into the body via a puncture on the skin. The agents get into the animal through the puncture.

v) Iatrogenic transmission route

This is the route introduced during medical operations like surgery, dehorning, castration. If the process is not aseptic then the disease takes advantage of it. (See definition of iatrogenic transmission here).

Prophylactic drugs may also cause infection if they are already contaminated before administration.

vi) Sexual transmission route

Common route for STDs in animals. Common in herds with natural breeding systems.

How to maintain an infection

Maintenance of an infection is done for the purpose of propagating the infectious agent. It is achieved through two major processes namely:

a) Host relationship

Parasitic – they multiply and affect the animal e.g. ticks.

Symbiotic – agent gets into the animal and coexist peacefully with the animal e.g. microflora in the rumen.

Commensalism – neither symbiotic nor parasitic. Either one is benefiting or not. None is harmful but depending on the conditions, they can become symbiotic or parasitic.

b) Transmission

They exit one host to another one before they are eradicated. Transmission can either be:

Horizontal – from one host to another

Vertical – spread from parent to the offspring through the placenta or spermatozoa of the male.

In some cases, the agent cannot exit from their host into another. The host is referred to as a Dead End Host. This breaks the maintenance of the host e.g. Rabbies in cattle.

Factors affecting disease transmission

a) Immunity of the host

A strong host prevents disease than a weak one.

b) Agent factors

Include the following:

Pathogenicity of the agent – ability of a microorganism to cause a disease.

Virulence – degree of pathogenicity of the microorganism.

These factors are influenced by the immunity of the host.

Body Defense Mechanisms

The body has two lines of defense mechanisms namely:

a) Physical barrier

i) Skin

Intact skin bars all microorganisms from the inner organs. There are a number of fatty acids on the skin that inactivates a number of microorganisms.

Sweat and other skin secretions have chemicals that do not allow multiplication of microorganisms.

Any disease-causing agent needs a break on the surface of the skin to gain entry to the organs under the skin.

Normal desquamation sheds off the microorganisms from the skin. Other secretions such as pus also dislodge microorganisms from the host.

ii) Respiratory tract

Contains cilia that trap big particles e.g. dust. The host then sneezes them out with the microorganism.

Goblet cells in the respiratory tract also produces mucus that trap microorganisms that are released through coughing.

Muco-cilliary actions – (cilia in the lower respiratory tract move the mucus upward when the animal lies down and coughs the mucus out. This process is called the escalator.

Macrophages – big cells at the terminal edges of the lungs, which engulf foreign materials and the phagocytize them.

Failure of these actions will lead to infection of the host due to weakening of the immune system.

Infection can also occur when the microorganism develops a special receptor site that they use to attach themselves on the cells.

iii) Gastro-intestinal Tract

The mouth produces saliva in large amounts, which dilutes whatever gets through the mouth. The saliva contains lysozyme, which deters microbial growth.

The GIT has an acidic pH, which is not conducive to microbial growth.

Mucus traps the disease-causing microorganism.

Peristalsis makes it hard for any organism to attach, penetrate, and cause diseases.

Most organisms in the GIT majorly exit the body through the faeces and mouth secretions.

iv) Urogenital system

Urine is sterile and keeps flushing and diluting the microorganisms. The anatomy of the urinary tract is long making it hard for the microorganism to reach the inner organs for the males.

The female system is shorter and more exposed making it easy for the microorganisms to access and cause infection. It has a pH of 5.0, which is acidic hence deters growth of microorganisms.

The udder hormone (oestrogen) also suppresses microbial growth.

STDs are introduced through coitus. They are expelled through urine (e.g. leptospirosis) and genital secretions.

v) Conjunctiva (eye membrane)

The eye has tear gland, which produces tears that wash the conjunctiva. The tears also contain enzymes that digest microbes. It also has eyelids that sweep the eye membrane periodically and involuntarily to keep the eye safe and clean.

Sometimes, microbes in the blood get to the eyes and cause infection on the eye membrane (systemic infection).

b) Immunological response

Immunity is the lack of susceptibility to infection or disease on the part of the host. Immunity can be either natural or acquired.

i) Natural immunity

The host is naturally immune to a particular disease or infection (e.g. zebu have naturally high immunity to anthrax).

Natural immunity can be specific to an individual or a particular species.

It may also be influenced by other factors such as age, heredity, nutrition, and environment.

ii) Acquired immunity

Can be divided into two types:

a) Cellular immunity

Involves the cells themselves and is more important in humans than in animals.

Once the body is under attack, the cells undergo alterations and acquire phagocytic ability.

b) Humoral immunity

Can be either active or passive.

i. Active acquired humoral immunity

An animal can acquire this type of immunity through recovery from a disease as a result of antigen-antibody reactions. Creation of antibodies prevents the animal from getting this disease.

It can also be acquired through vaccination. An attenuated/less-virulent form of the agent is introduced into the target animal to reduce virulence when the real diseases agent attacks the body.

After the introduction of the agent through vaccination, traces remain in the system and continue to produce the antibodies in the system of the host. This is termed as pre-immunity.

In other cases, the agent of the disease-causing microorganism is completely wiped off the system after complete recovery. This is termed as sterile immunity.

ii. Passive acquired humoral immunity

This is the immunity that is passively passed from one animal to the next. It is usually short term (3 -6 months) when compared to active immunity, which can be lifelong.

Methods of transferring immunity

  1. Transfusion
  2. Congenital transfer (through the placenta)
  3. Ovarian transfer
  4. Immunoglobulins transfer
  5. Colostrum transfer through the dam’s milk to the calf.

Disease Control Measures

Disease control is done with the major aim of ensuring that the animals are healthy so that they can produce and reproduce.

Different governments have measures in place to ensure that animal diseases are controlled to manageable levels.

General disease control measures:

a) Prevent occurrence

To prevent occurrence, there should be early detection, diagnosis, and treatment for the diseases e.g. mastitis and helminthiasis. They should be frequently checked.

Infer immunity to all animals by ensuring that:

  • All animals are properly fed
  • Sanitation is proper
  • Vaccination is done at the right time
  • The handlers handle the animals in an appropriate manner.
  • Control stress and disturbances

b) Prevent spread

Ensure the infection is contained to prevent spreading through the herd. You can achieve this by:

  • Isolation/quarantine
  • Maintaining high standards of hygiene
  • Proper handling of the animals
  • Vaccinating all the healthy animals
  • There is proper carcass disposal mechanism.

c) Prevent spread to man

Ensure there is minimal contact with the animals and animal products

Maintain high standards of hygiene.

Destruction is a control method that eliminates the host and the microbe. It has been used to control foot and mouth disease.

Public awareness through mass education is particularly important in containing foodborne and zoonotic diseases.

Bacterial Zoonoses: Classification, Diagnosis andControl

Zoonotic diseases are infectious diseases that are naturally transmitted between humans and animals. They can be transmitted by bacteria, fungi, viruses, or parasites. Bacteria are chiefly responsible for propagating bacterial zoonoses.

Some of them can cause serious diseases in people while others will not show any symptom. Since zoonotic diseases amount to over 200, diagnosis is important to identify the specific disease to ensure administration of correct treatment.

Effects of zoonotic diseases in animals and humans.

Some affect man and animals and can cause severe disease, even death e.g. anthrax

Others have little effect in animals but cause severe effects in man e.g. Q-fever and brucellosis

Others can cause severe disease in animals but almost invisible effects in man e.g. Newcastle and FMD

Transmission to man

Transmission majorly occurs during the clinical stage of the disease. The risk increases when the host animal is a career i.e. does not show symptoms.

Everybody is at risk of contracting zoonotic diseases. However, those who directly deal with animals and animal products are at an increased risk.

Other people who come into contact with materials that are easily contaminated by the animal products such as soil and water also have a higher risk of infections.

Farmers, anglers, sewage treatment workers, and veterinary officers must take extra care and use the personal protective gear while executing their duties.

Classification of zoonotic diseases

We classify zoonotic diseases according to the degree of host specificity. They include:

Arthropozoonosis – diseases transmitted from animals to man.

Zooarthropozoonosis – transmitted from man to animals.

Ampixenosis – transmitted either way (from man to animals and vice versa).

Classification according to the mode of transmission

a)      Direct zoonosis

These are transmissions perpetrated from one host to the other by either direct or indirect contact. These include diseases/infections like rabies.

b)      Cyclozoonosis

These diseases require an intermediate vertebrate host between man and animals e.g. taeniasis

c)      Metazoonosis

These diseases require an intermediate invertebrate host so that they become transmitters e.g. yellow fever and rift valley fever

d)     Saprozoonosis

Part of the developmental cycle of the disease-causing agent require inanimate reservoir to complete the metamorphosis e.g. hystaplasmosis and most fungal infections.

Classification according to causative agent

Here, there are either bacterial or viral zoonoses.

Bacterial zoonoses are as a result of a bacterial infection while viruses cause viral zoonoses.

Controlling zoonotic diseases

  1. Mass education in handling of infected animals is usually the most effective control measure. The public should be enlightened to minimize contact with animals and animal products and to use protective gear while handling animals, their products and byproducts.
  2. There should be strict rodent and vector control
  3. Public health officials should properly check meat meant for public consumption
  4. Proper cooking of all animal products especially meat from unfamiliar sources
  5. In the processing industry, there should be strict processing and hygiene procedures
  6. Avoid animal diseases at all costs

Bacterial Zoonoses

These are zoonoses attributed to bacteria. They include:

[A] Anthrax

Anthrax is a very critical infection that cause severe effects in both man and animals. It progresses rapidly and often leads to deaths of the victims.

Aetiology

The bacterium Bacillus anthracis is the causative agent. It is a gram positive, non-motile, and spore forming bacterium.

Soprulation occurs upon exposure of infected material to air. It is the bacteria’s form of defensive mechanism to avoid death. The spores are resistant to heightened salting, extremes of temperature and most disinfectants.

In the presence of organic matter, the bacteria get into the material or undrained alkaline soils. They thrive in warm climates for up to 60 years. Acidic soils reduce survival rates of the spores.

Anthrax in animals

Epidemiology

Anthrax affects all domestic animals as well as some wild animals. Ruminants are most susceptible, followed by the equine species. The porcine (pigs) species are the least affected.

When outbreaks occur, they are usually associated with soil borne infection after a major climatic change such as a heavy downpour after a prolonged drought.

Since the bacteria sporulate when exposed to air, it is advisable to never open up a carcass. Putrefaction usually destroys the bacteria.

However, there is still some level of risk, which the animals grazing in the fields assume.

Transmission

Transmission occurs through many routes including:

i) Ingesting contaminated feeds or water or soil.

Animals directly pick the spores from the mentioned sources. Water contamination is very common especially from the tannery effluent and contamination with infected carcass.

ii) Inhalation

Though a minor route, the animals can still get anthrax by inhaling spores in dusty air.

iii) Skin penetration

Needles used for treating animals can be a major route of transmission if it is used on multiple animals. Vectors can also transmit the disease through bite marks on the skin.

Clinical signs

Clinical signs can be described in two forms:

a.      Pre-acute form (1 – 2 hours)

Observable symptoms include:

  • Sudden death (within one and two hours)
  • Very high fever (42°C)
  • Muscle tremors
  • Severe dyspnea (difficulty in breathing)
  • Congested mucus membranes
  • Animal collapses and convulses before death
  • Immediately after death, the animal exudes a black tarry unclotting blood through the body orifices.
b.      Acute form (about 48 hours)
  • High fever (42°C)
  • Severe depression
  • Dyspnea
  • Congested mucus membranes
  • Animals completely lose appetite
  • Abortion in incalf animals
  • Drastic reduction in milk production (milk may have blood stains or a yellow taint)
  • Local oedema (usually of the tongue, throat, and the lower abdominal region)
  • Animal collapses, convulses and dies
  • After death, the animal exudes a tarry blood from the body orifices. The carcass lacks rigor mortis.

Post mortem lesions

Never perform post-mortem on the carcass.

You will know it is anthrax when the carcass exudes tarry blood and it lacks rigor mortis.

There is a rapid decomposition taking place in the carcass and the abdomen swells as a result. However, the limbs remain flaccid, i.e. “saw horse”.

If by any chance the carcass is opened up, you will observe echmotic haemorrhage and gross enlargement of the liver and the spleen (may double their usual sizes).

Anthrax in man

Humans also get affected through the same three routes. They include:

        i. Skin penetration

When infection occurs through skin penetration, the victim will get cutaneous anthrax. It is usually a professional hazard.

Lesions occur within two to three days after contact. You will first observe pimples (pastules) that collect fluid and becomes a vesicle surrounded by a zone of hyperaemia (reddening). The fluids will change into a bloody substance, which bursts to form blisters.

With progression, the area becomes blue-black and can easily peel off. You may also notice some fever and other general symptoms of disease.

People can easily recover from this form with or without treatment provided the bacteria does not get into the circulatory system.

      ii. Inhalation

Results into pneumonic or pulmonary anthrax.

It is common for people who work in dusty environment, especially in the wool industry. This is the reason it is called wool sorters’ disease”.

It results into a typical pneumonia. The victim shows the rapid onset of disease, high fever, dyspnea, and chest pains.

Bacteria in the blood travel to the heart and causes cardiac failure.

Bio-terrorists have used anthrax in the past in different parts of the world.

    iii. Ingestion route

Causes intestinal anthrax.

It occurs after consumption of meat from infected animals. Signs include:

  • Acute diarrhea
  • Severe abdominal pain
  • Death can easily occur

Diagnosis

Diagnosis is done the same way as in animals. To confirm the bacteria, isolate and identify it (gram positive and non-motile). You can also do cultural isolation of the bacteria.

Treatment

  1. Seek medical help as soon as possible.
  2. Use streptomycin and penicillin in high doses.
  3. Use antitoxins to neutralize the effects of the toxins.

Controlling Anthrax in animals

  • Prevent occurrence
  • Vaccinate animals annually and bi-annually
  • During outbreak, issue a notification and impose quarantine then isolate and treat all suspect cases during quarantine. Carefully handle all infected material (burry the carcasses without opening them up).
  • Add quick lime on the graves to avoid sporulation
  • When dealing with infected hides and skins, dispose them unless they are irradiated.
  • Use a very strong disinfectant (like formalin or Lysol) if you suspect sporulation.

Controlling Anthrax in Humans

  • Minimize contact with animals and use protective clothing if you have to contact them.
  • Proper meat inspection is critical.

[B] Brucellosis

This is a very important disease in both man and animals because it affects all animal species and all the corresponding bacteria will cause disease in humans.

Brucellosis in Cattle / Bovine Brucellosis

It is one of the easiest diseases to detect because it causes abortion in all affected pregnant females. In bovine, Brucellla abortus is the causative organism. They are gram-negative coco-bacilli bacteria.

It is a fairly sensitive bacterium that will be eliminated by ordinary environmental conditions such as sunlight and heat.

The bacteria can survive in the aborted material for long periods if kept under refrigeration.

Epidemiology

The disease has a global presence and majorly affects adult pregnant females. However, it is not limited to these potential victims alone.

The bacteria will be shed in milk, vaginal and uterine discharges, and in aborted material. The bacteria are also present in the semen of infected males.

Transmission

Transmission occurs through the following routes:

i) Ingestion

When animals drop their aborted material on the pastures, they cause contamination and become a risk to the rest of the herd that uses the same pastures for feeding. Calves are contaminated through the milk as well.

ii) Normal mating / coitus

The bacteria from the male get into the female through the semen.

iii) Artificial insemination

Artificial insemination can lead to transmission if contaminated equipment / semen are used. This route of transmission can be very catastrophic if undetected early enough.

Pathogenesis of Brucella abortus

It will move from the mucus membrane of the genital system and move into uterus via the circulatory system. In the uterus, the bacteria attack the endometrial cells and begin to multiply.

Once they have reached the attacking threshold, they move into the foetus through the umbilical cord. The effect on the endometrial cells will be so severe that the foetus will not be able to survive.

The bacteria will also lodge in other areas like the mammary glands leading to chronic mastitis. It can also get into the lymphatic system and cause inflammation of the lymph vessels.

In males, the bacteria will majorly affect the testis. The epididymis will be inflamed leading to blockage and such a male will be rendered infertile.

Summary signs
  1. Storm abortions in the third stage of the pregnancy. After one or two abortions, the animals get self cure.
  2. Males get sterility due to infertile ejaculations. In some instances, they may have reduced libido.

Diagnosis for Brucellosis

Tentative diagnosis is based on the clinical signs

Serological tests are easy to carry out and give evidence to the presence of the bacteria. Milk Ring Test (MRT) and Rose Bengal Test are quite effective and fast.

Bacterial isolation can also work. Take samples from any part of the animal e.g. vaginal swabs, or semen. The most commonly used sample is the foetal material after abortion.

Treatment and control measures in animals

Treatment is usually not necessary in animals due to self-cure. However, you should control the disease to prevent any incidence of an outbreak.

Vaccination is very effective. The vaccine uses strain 1a. Vaccinate the heifers before serving them.

Ensure the artificial insemination process is aseptic and proper.

Improve and maintain hygiene to prevent occurrence through ingestion. Properly dispose any aborted material that may contaminate the pastures.

Other species affected by brucellosis include:

SpeciesAetiologyClinical signs / zoonotic importance
SheepBrucella orvisMales will have painful epididymis and otitis or atrophy of the testis, which may also reduce the functionality of the organ
GoatsBrucella melitensisFemales abort. Causes severe brucellosis in man
SwineBrucella swissFemales will have either abortions or reduced litter. Males will have otitis of the testis. The bacteria localizes in the lymph nodes and muscles. Pork has very high levels of contamination of the bacteria. Contamination spreads during slaughter and it is impossible to identify it during meat inspection.

Brucellosis in Humans

Brucellosis in humans is also called ardulent fever or Malta fever. This is because brucellosis was first discovered in Malta, an island in the Mediterranean Sea. It is also called ardulent because it comes and goes.

Aetiology

All animal species are potential pathogens for man. People can get the disease via the following routes:

a) Ingestion

Consumption of raw / underpasteurized milk and milk products can lead to infection. Contaminated pork and other animal products is a viable route as well.

b) Skin penetration

Usually a professional hazard for those dealing with sick animals and aborted material

c) Conjunctiva

When you accidentally touch your eyes with your fingers after touching the contaminated material, there is a likelihood that the bacteria will get into your system.

Symptoms of brucellosis in man

This disease is usually confused with malaria due to the similarity in their symptoms. For this reason, many people tend to assume it leading to advanced infection.

It takes up to two weeks to manifest its symptoms after entering the host. The observable symptoms include:

  • Fever, which persists for many days. This is usually accompanied by body pains, which go away only to relapse after a few days.
  • Headaches
  • Constipation may occur
  • Dry cough due to infection of the bronchus
  • Characteristic night sweating
  • If the disease progresses without treatment, the organism will move to the joints and cause arthritis. The disease will not go away for more than 12 months.
  • There will be extreme loss of body weight due to improper feeding.
  • The fatality rates are rare.

Treatment for Brucellosis in man

Seek medical attention at the nearest hospital. It may require prolonged periods of treatment and the patient may be required to take medication for several months.

Controlling brucellosis in humans

Controlling this disease is most important. You can ensure the following:

  1. Proper handling of animals: – use protective clothing and avoid contact if you have an open wound
  2. In case of an abortion, properly dispose the aborted material as well as the placenta.
  3. Handle milk and milk products with a lot of care. Ensure the milk is properly pasteurized before consumption. Avoid raw milk and milk products.
  4. Ensure there is sufficient hygiene in milking parlours, processing plants, and even abattoir.
  5. Constantly test for the disease.

[C] Tuberculosis

Occurs in almost all animals in mild form and produces catastrophic consequences in humans. Tuberculosis simply means the formation of holes in the lungs. When the spaces break up and lodge in the capillaries, the situation can be fatal.

Aetiology

Mycobacterium tuberculosis is the causative microorganism that causes tuberculosis in cattle, sheep, and goats. All the species that affect the animals also affect humans. Mycobacteria are acid fast and resistant to a number of conditions.

Epidemiology

The disease is inapparent in animals. It is a big public health concern in humans because the bacteria are present in the urine, saliva, faeces, and uterine discharges. Since it is shed in milk, people may not be aware of its presence since the animals do not show any symptoms.

For animals:

Ingestion is the major route of transfer. Animals can also get it through coitus / during mating.

Urine and uterine discharges contaminate the pastures

For humans:

The major route of transmission is through inhalation, especially in a dusty environment. Consumption of contaminated milk from inapparent animal carriers is a huge risk since people will assume that the milk is not contaminated. The disease produces exact symptoms in man as in animals.

The bacteria are highly concentrated in the sputum.

Transmission is ampixenotic (i.e. animals transmit to man and vice versa as well as man to man and animal to animal). Transmission between man and dog is widespread due to their close association.

Spread between humans is very rapid.

This disease is prevalent among people living with HIV due to their compromised immunity.

Clinical signs in animals and man

The primary site of infection is in the lungs no matter what the route of transmission is. It produces pneumonia in the lungs with the following observable symptoms:

  • Constant coughing
  • Chest pains
  • Dyspnoea
  • Other signs are secondary to the infection of the lungs. The bacteria can localize in other body parts leading to other special diseases e.g.

Endometritis – when the bacteria attacks the uterus (the uterus will produce pus)

Mastitis – when the bacteria attacks the mammary gland. The bacteria will be continuously shed in milk during milking.

  • During coughing, people may spit blood due to rupturing of the blood vessels. The victim gets severe septicaemia and death follows.

Diagnosis of tuberculosis

Tentative diagnosis is based on the clinical signs.

For animals, post-mortem lesions from the carcasses can be useful for comprehensive diagnosis.

Confirmation of tuberculosis infection

Conduct tuberculin test – commonly done in animals to check even the carrier state. Get an extract. An interdermal injection will elicit a series of reactions leading to swelling that will be typical for a positive case.

The most common test for humans is cultural isolation of the sputum to confirm the causative bacteria.

Treatment of tuberculosis

The drugs used for treatment are exactly the same for humans and animals.

Treating animals is discouraged as the drug residues will find their way into humans leading to resistance. The resistance to drugs will make it practically impossible to treat sick people.

Isoniazid drugs are commonly used for the treatment. They are very strong and must be used over prolonged periods to eliminate the bacteria from the system.

Control measures

  1. Regular testing of animals using tuberculin test. Cull all positive animals; do not treat them.
  2. You can vaccinate the animals to prevent occurrence.
  3. Notify the public and quarantine in case of an outbreak. Ensure that products from these animals do not get to humans. Withhold milk and meat until there is clearance of drugs if any drug was administered.
  4. In humans, BCG vaccination is the most common method. BCG is usually an attenuated form of Mycobacterium bovis, which gives a lifelong protection.

[D] Bubonic Plague / Tauni (Black Death)

This is a very serious disease in humans even though it is not of much concern in domestic animals. However, rodents suffer severe disease when infected.

Aetiology

It is a bacterial zoonosis caused by Pasteurella pestis / Pasteurella yersinia. It is a gram negative rod-shaped coco-bacillus bacterium. These bacteria are quite prevalent in animals though they may not show the symptoms.

Epidemiology

It is a widely distributed disease that cause acute and fatal infections in humans and rodents. It exhibits sporadic occurrences. In Kenya, it has been reported in Machakos, Nairobi, and Mombasa.

Humans usually get it from rodents. In animals, dogs and cats are the most affected and are the ones associated with infections in humans. People get bitten by the fleas from these animals and rodents and transmit the disease to them in the process.

Clinical signs

Domestic animals usually manifest inapparent form of the disease (no observable symptoms). If they show any sign, it is very mild e.g. mild fever, low toxaemia, depression, and anorexia.

In rodents, deaths are common due to massive toxaemia.

Humans usually start to show signs one week after the bite. Observable symptoms include:

  • High fever
  • Swelling of lymph nodes, especially the inguinal lymph (in the thigh / groin area), that become painful after multiplication of the bacteria.
  • Toxaemia will set in followed by severe weakness.
  • Pneumonia will occur if the bacteria are localized in the lungs. This is considered secondary pneumonic plague, which is highly fatal and is transmissible between people. The primary disease comes from animals and is not transmissible between people.

Diagnosis

Suspect the disease from clinical signs

Confirm disease from bacterial isolation

Blood or sputum may be used if it has the pathogen

Treatment

  • Aim to treat man because they exhibit visible symptoms. Seek hospitalization for the patient.
  • Administer antibiotics such as streptomycin or tetracycline as advised by the medical officer.

Control measures for bubonic plague

  1. Avoid unnecessary contact with animals
  2. Eradicate fleas in animals
  3. Eradicate rodents from human habitation
  4. Vaccinate in prevalent cases

Bacterial zoonoses are hard to contain. They can wreak havoc and lead to massive losses of both income and lives.

Always seek professional advice when you suspect that your animal is suffering from any of these bacterial zoonoses.

Life is irreplaceable, seek medical attention if you spot any of the listed symptoms. It is always better to be safe than sorry.

Viral, Rickettsial and Parasitic Zoonoses: Diagnosis, Treatment, and Control Measures

Bacterial zoonoses pose a greater health risk to humans. Viral zoonoses compound the risk since they spread fast and are hard to contain.

On the other hand, other zoonoses like those of parasitic origin may not show any clinical symptom in their immediate host. When people consume products from such hosts, they get infected.

One perfect example is taeniasis, which does not show any clinical symptom in cattle. However, when they get into the human host, the worm multiplies rapidly and reach an attacking threshold.

It can cause damaging effects on the host since the human victims feel ashamed to admit that they have worms.

We are going to look at some viral, rickettsial and parasitic zoonoses of economic importance in the food industry. We will also look at their symptoms, diagnosis, treatment, and control measures.

Viral Zoonoses

1) Rabies

Viral zoonoses are acute and affect all warm-blooded animals and humans. The major characteristics of these diseases include hyper-excitability, paralysis, and death.

Aetiology of rabies

They are caused by an RNA virus that is very sensitive and will be inactivated by:

  • Getting it out of the host
  • Ordinary environmental conditions like heat and light
  • Disinfectants

It is however resistant to freezing. Freezing it actually preserves it.

Epidemiology of rabies

When a viral zoonose occurs in humans or animals, it will cause acute symptoms.

Carnivores tend to be the natural hosts of viral diseases. Infected animals have very high concentration of the virus in their saliva before any clinical sign of infection occurs.

Viral zoonoses have a global presence.

Transmission of rabies

Viral zoonoses spread through bites from the natural host or contact with body fluids from an infected warm-blooded host.

The GIT may also be a route though there aren’t any documented cases.

Pathogenesis of rabies

The virus is introduced through a bite. It into the peripheral nerve and moves to the central nervous system through motor action.

Clinical signs of rabies

The signs are typically manifested in dogs.

Onset of the disease varies with the site of the bite. Incubation period takes long period (3 – 8 weeks on average though it can be as short as 10 days or as long as 6 months).

The symptoms of the disease takes two forms in dogs:

  1. Furious form
  2. Dumb form

Furious form

This is the most common form of rabies in carnivores. It appears in three stages:

Prodromal phase
  • Takes 2 – 3 days
  • A slight increase in temperature
  • Dilation of the pupils
Excitable phase
  • Lasts 3 – 7 days
  • The animal is very alert and excited. It can move over very long distances while barking and biting until its voice becomes coarse.
Paralysis phase
  • Starts from the head moving down to the limbs.
  • Paralysis of the mouth leads to excessive salivation, dropped jaw, and the animal appear to choke whenever it tries to swallow anything.
  • When paralysis reaches the limbs, the animal will exhibit uncoordinated movement and it flops. Death will follow in 3 – 4 days.

Dumb form of rabies

The dog starts with the prodromal phase but skips the excitable phase. It goes straight to paralysis phase.

Rabies in cattle

Rabid cattle are furious. They bellow a lot and are aggressive but they do not bite. Paralysis and death follows eventually.

Cattle are dead-end hosts of rabies because they do not transmit it to any other host.

Rabies in humans

People get the disease from a carnivore’s bite. Incubation period is between 30 – 60 days, which also depends on the site of the bite.

Initial symptoms are usually general, e.g. headache, general malaise, slight fever, nervousness, anxiety, and a tingling sensation at the bite site.

After these signs, the characteristic symptoms for humans will set in. They include:

  • Hydrophobia (the victim fears water) due to the painful spasms in the pharyngeal muscles on attempt to swallow anything, including saliva.
  • Excitability
  • Convulsions will set in followed by paralysis and death.

Diagnosis of rabies

Confine animals suspected to have rabies. After their death, use their brain for diagnosis (check the negri bodies).

You can also do serological tests.

In humans, the patient’s history is very important in diagnosis.

Treatment of rabies

Once the disease has started in animals, it is untreatable. It will progress until the host dies.

In humans, give repeated vaccinations as soon as you realize the patient is suffering from rabies.

Control measures for rabies

  1. Prevent occurrence
  2. Vaccinate all carnivores
  3. Destroy all non-vaccinated wild and domestic carnivores when an outbreak notification is issued
  4. People at risk should receive regular vaccinations
  5. In case of an outbreak, issue a notification and pronounce quarantine then begin vaccination of all animals.

2) Rift Valley Fever

This disease was first diagnosed in Naivasha in 1931. It caused abortions in sheep and had high mortality rates of up to 95 percent.

In 1951, a similar syndrome occurred in South Africa in sheep. People who came into contact with the sick animals also got sick. One hundred people died and about 100 000 sheep and cattle were infected.

The disease then spread to other parts of Africa. No incident of this disease has ever been reported outside Africa.

Aetiology of rift valley fever

This disease is caused by the insect-borne arbovirus. This virus has high affinity for the liver hence it majorly affects the liver.

Transmission of rift valley fever

In animals, mosquitoes are majorly responsible for the transmission, though other insects are suspects as well.

People can be infected by handling aborted material from sick animals. Sick animals also shed the virus in milk, which becomes a route of transmission in humans. Human to human transmission is not documented.

How to recognize rift valley fever in animals

  • Incubation period lasts 1 – 2 days
  • High rates of abortion in sheep
  • High mortality rates (90 – 100%) in lambs. Most of the deaths occur within 36 hours of the onset of the disease.
  • Disease may also occur in mild form (no abortions, the animal just gets some diarrhea).
  • Discharge from the nostrils.

Manifestation of rift valley fever in humans

  1. People are susceptible to this disease once exposed to the infected material / affected animals. The most common transmission routes include handling of aborted material, the sick animals themselves, and the lab samples.
  2. Incubation period is 4 – 6 days
  3. Influenza (flu) like symptoms
  4. Flushed face for the light-skinned people
  5. Epigastric pain occurs in the advanced stages of the disease
  6. The eyes will be affected and the victims may experience blurred vision, photophobia, and blindness if death does not occur.
  7. Death is a very common occurrence in humans

Diagnosis of the rift valley fever

  • Clinical signs are very clear and provide a strong tentative diagnosis.
  • Take post-mortem lesions in dead cases.
  • Use necrotic hepatitis cells (dead cells) of the liver for diagnosis
  • Confirm the virus through viral isolation
  • You can also perform serological tests.

Control measures for the rift valley fever

  1. Prevent occurrence in animals by vaccination.
  2. Control insects, especially in breeding zones
  3. Carefully handle animals and animal products and byproducts
  4. Ensure minimal contact between animals and humans.

3) Haemorrhagic fevers (a group of diseases)

Majorly associated with monkeys. Cause haemorrhagic syndrome in humans.

Identification

1.      Yellow fever

Common in Africa, South America, and several other Asian countries

Aetiology of yellow fever

Caused by yellow fever virus. Natural hosts are primates. The virus is transmitted by insects from the primates to humans.

Forest workers and hunters are more susceptible.

The disease is apparent in animals but humans get severe symptoms such as:

  • Generalized haemorrhage affecting internal organs
  • High fever
  • Liver and kidney failure leading to severe jaundice and haemoglobinuria (haemoglobin in urine)
  • Death is common
Control measures for yellow fever
  1. Control mosquitoes
  2. Take precaution when dealing with primates
  3. Vaccinate in face of exposure

2.      Burbury fever

It is caused by a primate-associated virus. Lab workers are mostly affected and they contact the virus through aerial contamination.

Recognition of burbury fever

The disease is inapparent in animals but people experience acute fever, vomiting, and diarrhoea. Lymphadenopathy (swollen lymph nodes), haemorrhage, and death is quite common.

Control measures for burbury fever

Take a lot of care when handling patients

3.      Lassa fever

Lassa virus is responsible for causing Lassa fever. The virus is common in rodents and people contact it from them via aerial contamination.

Symptoms of lassa fever in humans
  • High fever
  • Vomiting and diarrhoea
  • Serious pneumonia, which starts as an inflammation of the upper respiratory tract
  • Haemorrhage
  • Death due to circulatory failure
Control measures for lassa fever
  • Control rodents
  • Vaccination
  • Ensure safety while handling patients

4.      Ebola fever

Ebola is a very severe and fatal disease in humans. It is associated with primates and is caused by the ebola virus, which has many strains including:

  1. Zaire sub-type (extremely severe)
  2. Reston
  3. Sudan
  4. Cote de Ivoire

It was first confirmed in the Democratic Republic of Congo (DRC) but has since spread to other parts. In DRC, it occurs mainly as the Zaire sub-type.

Transmission of ebola fever

It is transmitted through contact with the body fluid of an infected patient.

Symptoms of ebola fever
  1. Very high fever
  2. Severe weakness
  3. Back pain
  4. Headaches
  5. Diarrhoea
  6. Blood may ooze from body orifices
  7. People get rash
  8. Liver and kidney failure followed by death
Control measures for ebola fever
  1. Take a lot of care while handling patients
  2. Vaccination
  3. Reduce risk of sexual transmission
  4. Minimize contact with primates
  5. Practice outbreak containment e.g. proper burial (or cremation) of the dead

Rickettsial Zoonoses

1. Q-fever

This is a food-borne disease as well as a zoonose. It is common in most parts of the world.

In animals, it causes abortions and in humans, it causes serious disease.

It is a professional hazard for people dealing with livestock and those handling raw animal products.

Ticks are the main carriers and the pathogen will be found in the aborted material. It is also found in the placenta of cattle, sheep, and goats as well as in milk of these animals.

Aetiology of Q-fever

It is caused by a rickettsia microorganism Coxiellae burnettii.

Manifestation of Q-fever in animals
  • It is transmitted by tick bites. The sick animals exhibit the following symptoms:
  • High rate of abortions at any stage of the pregnancy
  • Inapparent / sub-clinical forms are also common in animals. The organism is shed in milk in this form posing danger to the human consumers.

Q-fever in humans

People get the disease as a professional hazard when they inhale or contact a sick animal and/or the aborted material.

Consuming contaminated milk and milk products is also a route of transmission.

Human to human transmission has not been recorded. However, the organism has been extracted from milks of mothers who have recovered from the disease.

Symptoms of Q-fever in humans

Incubation period lasts 2 – 4 weeks. Observable symptoms include:

  1. Sudden onset of influenza (flu) like syndrome (e.g. high fever, general malaise, weakness, depression, anorexia). This then progresses to,
  2. Dry cough
  3. Chest pain and dyspnoea due to pneumonia
  4. Jaundice since the liver is affected
  5. Fatality rates are very low. People recover after administration of drugs.
Diagnosis of Q-fever

Do serological tests for confirmation of the organism.

Isolate the microorganism from the aborted material.

Control measures for Q-fever
  1. Effective tick control
  2. Proper pasteurization of milk
  3. Wear personal protective gear while handling animals and animal products and byproducts
  4. Proper disposal of aborted material.

Other rickettsial zoonoses include:

  1. Epidemic typhis
  2. Murine typhis
  3. Rocky Murine typhis
  4. Spotted fever

Typhis fever affect both humans and animals, especially dogs. They are transmitted by ticks and fleas.

Dogs and monkeys do not get serious disease.

In humans, the patient may experience high fever, joint pains, muscle pain, swellings at the bite sites that may progress into ulcers.

Lymph nodes that are proximal to the bite site will swell.

Spontaneous recovery usually occur.

Summary of Ricketsial diseases and their vectors

Antigenic groupDisease causedActive speciesVectorImmediate hostWhere found

Anaplasma

Human anaplasmosisAnaplasma phagocytophilum
A. platys
A. ovis
“A. capra”
TickSmall mammals, rodents, deer
Dogs
Sheep
Goats
Primarily United States, worldwide
Venezuela
Cyprus, Iran
China

Ehrlichia

Human ehrlichosisEhrlichia chaffeensis
Ehrlichia muris
E. ewingii
E. canis
TickDeer, wild and domestic dogs, domestic ruminants, rodents
Dogs
Common in United States, possibly worldwide
Venezuela
NeoehrlichiaNeoehrlichiosisNeoehrlichia mikurensisTickRodentsEurope, Asia
NeorickettsiaSennetsu fever, neorickettsiosisNeorickettsia sennetsuTrematode (ingestion)FishJapan, Malaysia, possibly other parts of Asia

Scrub typhus

Scrub typhusOrientia tsutsugamushiLarval mite (chigger)RodentsAsia-Pacific region from maritime Russia and China to Indonesia and North Australia to Afghanistan

Spotted fever

RickettsiosisRickettsia aeschliman-
nii
TickUnknownSouth Africa, Morocco, Mediterranean littoral
African tick-bite feverR. africaeTickRuminantsSub-Saharan Africa, West Indies
RickettsialpoxR. akariMiteHouse mice, wild rodentsCountries of the former Soviet Union, South Africa, Korea, Turkey, Balkan countries, United States
Queensland tick typhusR. australisTickRodentsAustralia, Tasmania
Mediterranean spotted fever or Boutonneuse feverR. conoriiTickDogs, rodentsSouthern Europe, southern and western Asia, Africa, India
Cat flea rickettsiosisR. felisFleaDomestic cats, rodents, opossumsEurope, North and South America, Africa, Asia
Far Eastern spotted feverR. heilong-
jiangensis
TickRodentsFar East of Russia, Northern China, eastern Asia
Aneruptive feverR. helveticaTickRodentsCentral and northern Europe, Asia
Flinders Island spotted fever, Thai tick typhusR. honei, including strain “marmionii”TickRodents, reptilesAustralia, Thailand
Japanese spotted feverR. japonicaTickRodentsJapan
Mediterranean spotted fever-like diseaseR. massiliaeTickUnknownFrance, Greece, Spain, Portugal, Switzerland, Siciliy, central Africa, Mali, and Argentina
Mediterranean spotted fever-like illnessR. monacensisTickLizards, possibly birdsEurope, North Africa
Maculatum infection; Tidewater spotted fever; American boutonneuse feverR. parkeriTickRodentsNorth and South America
Tickborne lymphadenopathy, Dermcentor-borne necrosis and lymphadenopathyR. raoultiiTickUnknownEurope, Asia
Rocky Mountain spotted fever
Brazilian spotted fever
R. rickettsiaTickRodentsNorth, Central, and South America
North Asian tick typhus, Siberian tick typhusR. sibiricaTickRodentsRussia, China, Mongolia
Lymphangitis-associated rickettsiosisR. sibirica mongolotimonaeTickRodentsSouthern France, Portugal, China, Africa
Tickborne lymphaden-
opathy (TIBOLA), Dermacentor-borne necrosis and lymphaden-
opathy (DEBONEL)
R. slovacaTickLagomorphs, rodentsSouthern and eastern Europe, Asia

Typhus fever

Epidemic typhus, sylvatic typhus

 

 

 

Murine typhus, fleaborne typhus

R. prowazekii

 

 

 

 

R. typhi

Human body louse, flying squirrel ecto-
parasites, possibly some ticksFlea
Humans, flying squirrels

 

 

 

Rodents

Central Africa; Asia; Central, North, and South America

 

 

Tropical and subtropical areas worldwide

Table Source: CDC

Chlamydial Zoonoses

1. Psittacosis / Ornithosis

Psittacosis is derived from the Greek word psittacus, which means parrot. Te disease is associated with parrots. Ornithosis means it is associated with birds.

The disease is simply referred to as psittacosis in humans regardless of the source. People get it by direct contact with sick birds.

The causative organism is Chlamydia psittaci.

Manifestation of ornithosis/ psittacosis in birds

The responsible chlamydia is a common flora in birds hence there only needs to be a change in the physiological conditions of the bird for the organism to attack.

Stressed birds will develop the disease. Stress can arise from different sources including transportation or noise. Affected birds will exhibit the following symptoms:

  • Diarrhoea
  • Dullness
  • Hurdling together
  • Ruffled feathers

During the active stage of the disease, the microorganism is highly concentrated in the faeces, which becomes the major source of contamination.

Manifestation of ornithosis/ psittacosis in humans

People get the disease through contact with sick birds during the active stage of the disease.

Human to human transmission occurs, though not very common. The chlamydia can be air-borne.

Symptoms of ornithosis in humans

Incubation usually takes between 1 – 2 weeks after exposure. The symptoms then commence as a typical pneumonia. Observable symptoms include:

  1. High fever
  2. Dry cough
  3. Chest pains
  4. Dyspnoea
  5. Severe headaches
  6. Hepatitis due to the effect on the liver
  7. When the chlamydia travels to the brain, it causes mental confusion that progresses into a coma
  8. Myocarditis (inflammation of the heart) leading to heart failure
Diagnosis of ornithosis

Conduct routine checks in animals. Isolate sick birds for confirmation.

In humans, perform lab tests at the hospital.

Treatment of ornithosis

In birds, do prophylactic treatment (give them oxytetracycline)

People should get prescription form the hospital. Usually, oxytetracycline is given.

Control measures for ornithosis
  1. In birds, conduct regular testing and treatment.
  2. Avoid predisposing factors (e.g. stressing the birds) as much as possible. Do prophylaxis before exposing the birds to stressful situations.
  3. Avoid faecal contamination of birds’ feed and water.
  4. In humans, ensure careful handling of birds whether they are sick or just normal.

Parasitic Zoonoses

1. Taeniasis / Cysticercosis

Parasitic zoonoses are associated with meat. Psychrozoonoses require more than one vertebrate host to cause a disease.

Adult parasite (tapeworm) causes taeniasis while the larval stage causes cysticercosis. The adult stage is usually hosted by humans while the larval stage is found in animals (especially the domesticated ones).

The intermediate host is domestic animals like cattle and shoats (sheep and goats).

There are two prominent species of the tapeworm:

  1. Taenia solium
  2. Taenia saginata

T. saginata majorly inhabits cattle but can also be found in other animals.

Cysticercosis in cattle is attributed to Cysticercus bovis (bovine) and Cysticercus cellulosae (pigs). Wild animals can also get Cysticercus bovis.

People can harbour both the larval and adult stages of Taenia solium. Humans are the immediate and permanent host of the worm. Human to human transmission does not occur.

Taenia solium eggs are transferred to other hosts through food.

Life cycle of Taenia spp. worm

The life cycle of these two worms can begin anywhere within the cycle.

Clinical signs and symptoms of taeniasis
  • Taeniasis in an adult human being is asymptomatic except for pains and weight loss. High infection in children will cause other symptoms. Ulcer pains due to hooks in the intestines that cause bleeding.
  • Diarrhoea with dysentery
  • Nausea and vomiting in adults
  • Psychological disturbance (adults do not want to admit that they have worms).
  • The larval stage of Taenia solium will produce serious signs, especially when it gets into the brain.
  • Some of the observable symptoms include:
  • Severe headache
  • Nausea and vomiting
  • Blurred vision that may lead to blindness
  • Feeling of numbness
  • Cystircercosis in animals will be manifested as cysts in the masseter muscles and cardiac muscles.
  • The disease in animals may be sub-clinical, only to be noted during post-mortem.
Diagnosis of taeniasis

Analyse the stool for the eggs in humans.

In animals, conduct post-mortem tests and evaluate the cyst count. If the cyst count is less than 10, the meat is not condemned but sold under instruction. If the cyst count is greater than 20, condemn the meat.

Treatment of taeniasis

In animals, the disease is not treated as they do not show clinical signs.

People should undergo regular deworming to eradicate the worm.

Control measures for taeniasis
  1. Inspect meat before consumption.
  2. Proper disposal of human waste
  3. Cook meat properly before consumption
  4. Regular deworming of people (3 months interval).

2. Hydatidosis / Echnococcosis

Hydatidosis is caused by hydatid cyst. The larval stage affects both humans and animals.

Echnococcosis is caused by two strains of echnococcus that inhabit dogs. The two strains are:

  1. Echnococcus granulosus
  2. Echnococcus multicularis

Humans are dead-end hosts for this parasite because dogs do not feed on human viscera.

Life cycle of the hydatid parasite
Symptoms of hydatidosis in dogs
  1. Severe enteritis under severe infestation
  2. Diarrhoea with blood
  3. Anaemia in young puppies
  4. Rough hair coat

Other domestic animals may have the cyst in the internal organs but do not show any clinical signs.

Clinical signs of hydatidosis in humans
  1. The cysts cause organ enlargement leading to an enlarged abdomen
  2. Organ failure may occur depending on the level of infestation
  3. When the severity reaches the CNS, nervous symptoms occur.
Diagnosis of hydatidosis
  • Use faecal sample for analysis.
  • It is not possible to diagnose domestic animals. The cysts will be seen in the organs when the animals die.
  • In humans, suspect the disease from the symptoms, especially abdominal enlargement.
  • Confirmation of infection by scanning the organs for cysts. Serological tests are also applicable.
Treatment of hydatidosis
  • Deworm dogs using an anthelmintic
  • Domestic animals do not show symptoms hence no treatment
  • In humans, surgical procedures are applicable. The procedure should be very delicate because the worms contain a very toxic fluid.
Control measures for hydatidosis
  1. Proper meat inspection
  2. Regular deworming of dogs
  3. Minimize contact between humans and dogs
Summary table for the three worms
Adult hostDefinitive hostOrgans affectedLarval stageIntermediate hostOrgans affected
T. saginataManIntestinesC. bovisShoats & cattleActive muscles (e.g. tongue, diaphragm
T. soliumManIntestinesC. cellulosaePigsMuscles
EchnococcusDogIntestinesHydatid cystHumans & domestic animalsSoft organs like liver

Toxoplasmosis

This is a protozoan disease that affect all domestic animals. The infection is critical when the infection enters the cat because the cat hosts the infective stage of the disease.

The causative protozoan is Toxoplasma gondii.

The cat being the definitive host of the microorganism sheds the oocytes through the faeces. The oocytes sporulate once they come into contact with air.

Humans get the infection through the spores since they have a close association with cats. They can get into contact with the spores through:

  1. Consumption of contaminated foods
  2. Inhaling the spores in the air
  3. Congenital transmission (mother to child through the placenta)

Clinical signs of toxoplasmosis in animals

  1. Animals exhibit the inapparent form of the disease.
  2. Epidemics occur in rare cases when the disease occur in chickens, pigs, and rabbits
  3. In shoats (sheep and goats), the disease trigger abortions

Clinical signs of toxoplasmosis in humans

Symptoms usually vary with age.

  1. Adults get inapparent form of the disease
  2. Pregnancy in women activates the disease and the patient has pneumonia and swollen lymph nodes. The CNS may be affected and the pregnancy may end up in an abortion or a stillbirth.
  3. Babies born of infected mothers’ exhibit generalized infections immediately after birth. They developed enlarged liver and spleen and may experience convulsions. Babies who survive may be mentally retarded.
  4. Young children who acquire the infection from a cat may experience general malaise and mild infections.

Diagnosis of toxoplasmosis

In animals, examine the faecal sample for the oocytes.

In humans, perform serological tests.

Control measures for toxoplasmosis

  1. Pregnant women should ensure strict and paramount hygiene when handling cats
  2. Young children should avoid close contact with cats
  3. People should avoid raw and under-cooked meat
  4. Avoid feeding cats with raw meat
  5. Control vectors such as flies and cockroaches.

Trichinellosis

Trichinellosis is a parasitic zoonotic disease that is directly transmitted from animals to humans. The causative organism is a nematode called Trichinella spiralis.

Epidemiology of trichinellosis

The disease majorly occurs in the northern hemisphere. It is very prevalent in Alaska and places where people love wild boar and bear meat.

Horses also get the disease. Dogs, cats, and other carnivores also get the disease but they may not transmit it to humans.

Life cycle of the Trichinella spp. nematode

The disease undergoes a similar cycle in humans as in animals.

People get the cyst from boar/bear/horse meat. When the cyst gets into the stomach, it vegetates and grows into an adult. It then passes into the intestines where it lays eggs.

Immature larvae will get into the blood and then pass into the muscles.

Sources of trichinella infection

This disease is majorly transmitted through garbage and feeding. Some of the most common routes of transmission include:

  1. Consumption of raw / improperly cooked meat (from boar/bear/horse)
  2. People who feed garbage to pigs perpetrate the disease
  3. Birds eat garbage and spread the disease through their eggs and droppings
  4. Domestic animals may also get and transmit the disease when they scavenge through garbage.

Symptoms of trichinellosis in humans

When the nematode is still in larval stage, the patient may experience the following:

  1. Nausea
  2. Abdominal discomfort
  3. Fever
  4. Headaches
  5. Facial oedema
  6. Itchy skin
  7. Myositis in the muscles (irritation and pain of the muscles)
  8. Pain and irritation of the tongue, masseter muscles, diaphragm, and the heart muscles
  9. If the disease reaches the lungs, the patient will experience dyspnoea and coughing.
  10. The patient may feel tired due to improper circulation when the disease affects the heart.

Symptoms of trichinellosis in animals

The adult parasite resides in the stomach. The sick animal will show the following signs:

  1. Abdominal discomfort
  2. Diarrhoea
  3. General sickness
  4. Myositis in the muscles depending on the affected muscles
  5. Difficulty in breathing if the disease affects the diaphragm
  6. When the disease affects the masseter muscles, the animal will have difficulty in feeding
  7. The animal will tire if the heart is affected

Diagnosis of trichinellosis

Examine the faecal sample for the eggs of the parasite.

Treatment of trichinellosis

Regularly deworm the animals and people

Break the cycle of the nematode to discontinue infection cycle.

Control measures for trichinellosis

  1. Regular testing and treatment of sick patients. Treat any animal in whose faecal sample you find one egg
  2. Proper garbage disposal and management
  3. Avoid feeding pigs on garbage
  4. Proper cooking of meat
  5. Deep freezing can help eliminate the parasite.

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