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DEPARTMENT: AGRICULTUREREPUBLIC OF SOUTH AFRICA

In order to understand what causes disease inanimals, we first need to know what diseaseis. Disease (also known as sickness) is anyprocess that interferes with the way thedifferent parts of the body work and look.We do not normally consider injuries suchas broken legs and cuts as diseases.

Causes of disease in animalsThere are many causes of disease in animals.Knowledge of what causes disease, and of howanimals can get a disease, helps us to know howto prevent disease and to treat sick animals.

ParasitesParasites are organisms that have to live on or inother organisms, such as animals, in order tosurvive. Most parasites are easy to see, althoughsome mites and the early stages of worms canonly be seen under a microscope.

CAUSES OF DISEASEIN ANIMALS– JENNY TURTON –

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EXTERNAL PARASITES

Flies, lice, fleas, ticks and mites can causeserious diseases in animals.

Some live on the animals for their entire lives,others only spend part of their lives there,while others only visit to feed.

They can result in irritation and skin damagein animals. Some parasites can also passdiseases such as redwater and three-daystiffsickness between animals.

INTERNAL PARASITES

Internal parasites (including roundworms,flukes and tapeworms) can cause seriousdiseases and loss of production in animals.

They usually live in the stomach and intestinesbut also in other parts of the body such as thelungs and liver.

Microbes (germs)

Microbes (germs) are usually too small to beseen with the naked eye, and only a micros-cope will enable you to see what a microbelooks like.

Just because you do not see microbes withyour naked eye, does not mean that theycannot cause disease in your animals.

Scab mite

Bont tick

Tape worm

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Some microbes are harmless. For example,bacteria surround animals and people,and they even live on our skin and inside ournose, mouth and stomach, but thesebacteria do not normally cause problems.

Some microbes are even helpful, such as theones in our gut which help us to digest food.

Many different microbes can cause diseasein animals, and there are four main types:

VIRUSES

Viruses are the smallest of all microbes.

They must live inside cells in order to surviveand breed.

Viruses cause about 60 % of disease outbreaksin animals and humans.

Examples of diseases in animals caused byviruses are rabies, Newcastle disease andthree-day stiffsickness.

It is difficult to treat diseases caused by virusesbecause the viruses live inside animal cells.Therefore, any medicine that can kill theviruses will also harm the animals in whichthe viruses are present.

BACTERIA

Bacteria can live in animals and in theenvironment.

Dog withrabies

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Not all bacteria cause disease.

People and animals have bacteria living onand in them that do not cause disease.

Examples of diseasesin animals causedby bacteria areanthrax, black-quarter andtuberculosis.

Bacteria can infectwounds, and that iswhy wounds should be treated.

FUNGI

Fungi occur widespread in the environment(soil, air and water) and include mould onstale food and mushrooms.

Fungi need to grow on organic material inorder to feed, and this can include animalsand people.

An example of a fungal disease in animals isringworm.

Some fungi are normally harmless, but cancause disease in some situations, especiallyafter prolonged use of antibiotics.

Some fungi can also produce toxins or poisonswhich can be a problem when food becomesstale or wet.

Blackquarter

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PROTOZOA

Some protozoa can live outside cells, especiallythe type that causes trichomonosis, a venerealdisease in cattle. Others need to live insidecells, and include those causing coccidiosis,redwater, heartwater and gallsickness.

PoisoningAnimals can be poisoned by chemicals (suchas insecticides and dips), poisonous plantsand fungal toxins.

They can also be poisoned when bitten bysnakes, scorpions and spiders.

Dietary problemsLack of enough food or lack of a particularpart of the food (such as phosphorus) canalso cause disease.

Malnourished animals may develop otherdiseases because they are weak.

Metabolic diseasesMetabolic diseases are an upset in the normalfunctioning of the animal (that is not causedby infection, poisoning or feed deficiencies)and usually result from intensive animalproduction.

An example is milk fever in highly-productivedairy cows.

Iodinedeficiency

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Congenital diseases

In some cases animals can be born with adisease. Some of these may be inherited(passed on from the parents). This is rare,and inherited diseases are usually seen atbirth. An example is congenital hydrocephalus,which is a swelling of the brain caused byfluid, and can be clearly seen as a swellingof the head.

Environmental diseases

Environmental problems, such aslittering, contribute to somediseases, for example, animalsmay eat plastic bags or wires andthis can harm the animalís health.

Cancer

Cancer occurs when some of the cells in thebody grow in a way that is different from normal.Illness occurs because of the pressure of thegrowth on other parts of the body and the factthat affected parts of the body cannot functionnormally.

Cancer can also cause signs such as feverand loss of condition.

In some instances viruses can causecancer.

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Allergies

Some diseases are caused by allergies,which is when the bodyís own immunesystem attacks part of the body.

Degenerative disease

Some diseases are caused by parts of thebody breaking down, particularly as ananimal becomes older.

How to prevent disease

Good management, which includes goodhygiene and sufficient feed, can reduce thechances of animals getting disease.

In some cases vaccination and practicessuch as dipping and deworming can alsoprevent disease.

Information provided byAnimal Health for Developing FarmersARC-Onderstepoort Veterinary InstitutePrivate Bag X05, Onderstepoort 0110

Tel. (012) 529 9158

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2004 Second print2000 First print

Compiled byDirectorate Agricultural Information ServicesDepartment of Agriculture

in cooperation withARC-Onderstepoort Veterinary Institute

Printed and published byDepartment of Agriculture

and obtainable fromResource CentreDirectorate Agricultural Information ServicesPrivate Bag X144, Pretoria 0001, South Africa

This publication is available on the web at:

www.nda.agric.za/publications

For further information contact your nearestanimal health technician or state/privateveterinarian

or

Animal Health for Developing FarmersARC-Onderstepoort Veterinary InstitutePrivate Bag X05, Onderstepoort 0110Tel: (012) 529 9158 Fax: (012) 529 9427

or

Resource CentreDepartment of AgricultureTel: (012) 319 7141/7085