Animal Diseases – JSS3 Agricultural Science Lesson Note (First Term)

What is animal disease?

Animal disease is an impairment of the normal state of an animal that interrupts or modifies its vital functions.

• Healthy animal: eats well, is alert, moves freely and grows or produces normally.
• Diseased animal: shows signs of illness and produces less meat, milk or eggs.
• Importance to farmers: disease causes deaths, loss of income and poor-quality products.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define animal disease;
2. state the main causes of animal diseases;
3. name common viral diseases of farm animals;
4. state the animals that each disease affects;
5. state the cause of each disease where it is given in the note;
6. list ways of preventing and controlling animal diseases.

What are the key terms used in animal diseases?

Key terms are the words students must know before studying the diseases.

• Pathogen: a living organism or virus that causes disease.
• Virus: a very small germ that multiplies inside the living cells of a host.
• Contagious disease: a disease that spreads easily from one animal to another.
• Infectious disease: a disease caused by a pathogen that can enter and multiply in an animal.
• Vector: an insect or tick that carries a pathogen from one animal to another.
• Zoonosis: a disease that can pass from animals to humans.
• Ruminant: an animal that chews the cud, such as cattle, sheep and goats.
• Cloven-hoofed animal: an animal with a split hoof, such as cattle, goats, sheep and pigs.
• Mortality: the number of deaths in a group of animals.

What causes animal diseases?

Animal diseases are caused by pathogens, parasites, poor feeding, injury and inherited faults.

• Viruses: cause diseases such as Newcastle disease and foot and mouth disease.
• Bacteria: cause diseases such as anthrax.
• Protozoa: cause diseases such as trypanosomiasis (spread by tsetse flies) and coccidiosis.
• Parasites: worms, ticks, lice and mites live on or in the animal and weaken it.
• Poor nutrition: lack of a nutrient in the feed causes deficiency diseases such as rickets.
• Injury and poisoning: wounds, accidents and poisonous plants harm the animal.
• Inherited faults: some defects pass from parents to young animals.

What are the types of animal diseases?

There are two main types of animal disease: infectious diseases and non-infectious diseases.

Infectious diseases

• Cause: pathogens such as viruses, bacteria and protozoa.
• Spread: pass from sick animals to healthy ones, directly or through vectors.
• Examples: Newcastle disease, foot and mouth disease, peste des petits ruminants.

Non-infectious diseases

• Cause: poor feeding, injury, poisoning or inherited faults.
• Spread: do not pass from one animal to another.
• Examples: rickets and other deficiency diseases.

What are some common viral diseases of farm animals?

The diseases below are all caused by viruses and affect farm animals.

African horse sickness

• Meaning: African horse sickness (AHS) is a highly fatal, non-contagious, infectious disease.
• Animals affected: horses, mules and donkeys.
• Cause: the AHS virus, spread by biting insects (midges).

African swine fever

• Meaning: African swine fever (ASF) is a haemorrhagic fever of domestic pigs.
• Animals affected: domestic pigs.
• Effect: usually causes very high mortality within a short time after infection.

Avian influenza

• Meaning: avian influenza is a flu disease of birds.
• Animals affected: birds, including poultry.
• Cause: influenza (flu) viruses (AIV).
• Note: the viruses frequently replicate among birds in a form of low pathogenicity (LPAIV).

Bluetongue

• Meaning: bluetongue (BT) is a ruminant disease.
• Animals affected: ruminants such as cattle, sheep and goats.
• Cause: an Orbivirus transmitted by midges.
• Note: there are at least 24 serotypes of the bluetongue virus.

Classical swine fever

• Meaning: classical swine fever (CSF), or hog cholera, is a highly contagious viral disease.
• Animals affected: swine (pigs and wild boar).

Crimean-Congo haemorrhagic fever

• Meaning: Crimean-Congo haemorrhagic fever (CCHF) is a tick-borne viral disease.
• Cause: a Nairovirus in the family Bunyaviridae.
• Vector: ticks.

Foot and mouth disease

• Meaning: foot and mouth disease (FMD) is a contagious viral disease.
• Animals affected: cloven-hoofed animals, to which it can spread rapidly.

Lumpy skin disease

• Meaning: lumpy skin disease is a viral disease of ruminants.
• Cause: a pox virus of the genus Capripoxvirus.
• Note: the genus Capripoxvirus has three viruses affecting ruminants.

Newcastle disease

• Meaning: Newcastle disease (ND) is a contagious viral disease.
• Animals affected: many species of birds.
• Cause: a virus of the family Paramyxoviridae.

Peste des petits ruminants

• Meaning: peste des petits ruminants (PPR) is a contagious viral disease.
• Animals affected: mainly small ruminants (goats and sheep).
• Effect: causes heavy losses to farmers.

Rift Valley fever

• Meaning: Rift Valley fever (RVF) is a viral zoonosis.
• Animals affected: it primarily affects animals.
• Human risk: it can also infect humans.

Rinderpest

• Meaning: rinderpest causes an acute and often fatal disease.
• Animals affected: cattle and other ruminants.
• Cause: rinderpest virus (RPV), a member of the genus Morbillivirus in the family Paramyxoviridae.

Schmallenberg virus

• Meaning: Schmallenberg virus (SBV) causes congenital malformations and stillbirths.
• Animals affected: cattle, sheep, goats, bison and possibly camelids.

What is the quick summary of animals affected by each disease?

The table shows the main animals affected by each disease in this note.

What are the signs of a sick animal?

A sick animal shows changes in its appearance, behaviour and body functions.

• Loss of appetite: the animal refuses feed and water.
• Dullness: the animal is weak, stays alone and hangs its head.
• Abnormal discharge: fluid flows from the eyes, nose or mouth.
• Diarrhoea: droppings are watery or contain blood.
• Breathing and coughing: the animal breathes with difficulty or coughs.
• Rough coat or dull feathers: hair or feathers lose their shine.
• Fall in production: less milk, fewer eggs or loss of weight.

How do animal diseases spread?

Diseases spread from sick animals to healthy animals in several ways.

• Direct contact: healthy animals touch or mix with sick animals.
• Contaminated feed and water: pathogens enter the animal through food or drink.
• Vectors: midges, ticks and other insects carry the pathogen.
• Air: some pathogens travel in droplets when animals cough.
• Dirty equipment and clothing: tools, vehicles and boots carry germs between pens.
• New animals: a newly bought sick animal brings disease into the herd or flock.

How can animal diseases be prevented and controlled?

Animal diseases are prevented and controlled by good management and by following veterinary advice.

1. Vaccinate: give animals vaccines on time, for example against Newcastle disease.
2. Quarantine: keep new animals apart before joining the herd or flock.
3. Isolate sick animals: separate them at once from healthy ones.
4. Keep pens clean: clean and disinfect houses, feeders and drinkers.
5. Feed well: give balanced feed and clean water to build resistance.
6. Control vectors: dip or spray against ticks and reduce midges and other insects.
7. Dispose of dead animals: bury or burn carcasses properly.
8. Call a veterinary doctor: report unusual illness or sudden deaths quickly.

Evaluation

1. Define animal disease.
2. Name the animals affected by African horse sickness.
3. Which insects transmit bluetongue?
4. Which virus family causes Newcastle disease?
5. Which disease mainly affects goats and sheep?

Assignment

Choose any three diseases from this note. For each one, write the animals it affects and what causes it.