STANDARD METHOD OF DISEASE DIAGNOSIS IN FARM ANIMALS

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.

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.

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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.

Body regions

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.

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.

Thorax

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

Abdomen

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

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.

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.

Limbs

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

Body systems

Respiratory system

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

Gastro-intestinal Tract (GIT)

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

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.

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.

Skeletal system

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

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:

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).

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.

Ballottement (tactile percussion)

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

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.

Auscultation and percussion

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

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

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.

Rectal palpation

Useful for pregnancy diagnosis and deformities in organs.

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.

• 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).

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.

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

Methods of disease transmission

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).

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.

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.

Experimental transmission

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

Ingestion

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

Inhalation

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

Contact (mucus membrane)

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

Inoculation

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

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

Sexual transmission route

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

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.

Immunity of the host

A strong host prevents disease than a weak one.

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.

The body has two lines of defense mechanisms namely:

Physical barrier

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.

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.

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.

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.

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).

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.

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.

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.

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 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

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

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.

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.

Reference-on request