Animal Health and Diseases Agricultural Sciences Grade 12 Study Guides and Notes

Animal Health and Diseases Agricultural Sciences Grade 12 Study Guides and Notes. Disease is one of the most common threats to animal wellbeing. It’s estimated that one in five farm animals are lost due to diseases each year, while many more animals suffer the effects of illness.

Animal health products help protect, diagnose and treat animals against disease. Medicines alleviate the suffering of the animal, boost healthy productivity and ensure fewer animals are lost to disease.

Overview

Animal Health

1. Signs of poor health/sick animals

• We can tell if animals are in poor health or sick by
• comparing their normal behaviour and functions with their behaviour and functions when they do not seem well.

A clinical examination is when you examine animals for signs of disease. One of the ways of examining a sick animal is to use a rectal thermometer which is used to take the temperature of mammals.

Signs of poor health/sickness in ruminants (cattle, sheep and goats)

Signs of poor health/sickness in pigs

Signs of poor health/sickness in poultry

2. Methods of testing animal health
Methods to investigate, test or diagnose suspected ill health in an animal or herd.

Clinical examination

• A clinical examination of an animal is done to help determine the cause of a disease or make a diagnosis. This involves the examination of various body parts and functions. This is important because similar symptoms can be seen in diseases or conditions that have different causes.

Laboratory tests

• Various laboratory tests can be done on live animals to help make a diagnosis.
• Blood smears: These can be made to diagnose diseases like anthrax or various blood-borne diseases in which parasites can be seen in blood cells.
• Serology: Blood samples can be tested for antibodies to infectious agents.
• Cultures: You can do a culture for an infectious agent. This involves the growth of the culturing material in a laboratory from an abscess or a milk sample in order to identify the bacteria that caused it.
• Faecal examination: Faecal samples can be tested for signs of roundworm and fluke eggs will indicate the severity of the infestation.

Postmortem

• A postmortem (or PM) is the procedure when you cut open the carcass of a dead animal to determine the cause of death.
• The cause may be obvious such as when a large number of internal parasites are found. But if no macroscopic signs are found, then
• samples must be taken for microscopic examination of tissue samples to determine a specific diagnosis → This is called histology.

3. Methods of administering medicine to animals

Injections (can be intravenous, intramuscular or subcutaneous)

• Sick animals suffering from bacterial infections can be treated with injections of antibiotics. Some worm remedies are either injected as a once-off treatment or given on a sustained basis as part of a worm control programme.

Dosing

• Dosing is when remedies are given by mouth. These treatments include worming remedies, diarrhoea medications and antibiotics. Worm remedies can be used as a once-off treatment or on a sustained basis as part of a programme. Dosing must be done correctly to ensure that the animal is not harmed.

Vaccinations

• Vaccinations are used to prevent various diseases. Most vaccines are injected subcutaneously or intramuscularly. In poultry some vaccines are applied as eye drops or a spray which is inhaled by the birds.

In-feeds

• Some medications are given in the animal feed. This method is used for some growth promotants or antibiotics given to prevent infections in animals. It is often done on a sustained basis in intensive animal production systems.

Dipping

• Animals can either be dipped or the dip can be applied by spray or pour-on methods. This is used mainly to treat or control external parasites.

Footbaths

• Can be used to control ticks found on the feet of animals. It can also be used to treat and prevent diseases such as foot rot in sheep or cattle.

Sustainable use of medication Sustainable medication (SM) in agriculture combines the advantages of modern, traditional and complementary treatment systems, to provide better healthcare services for livestock.
Its basic characteristic is to form a preventive and affordable system from a combination of the best of modern and traditional medicine, integrating the latest technology to access and utilise the benefits of Indigenous Knowledge Systems related to the care and treatment of livestock. A further characteristic of SM is the fact that the main therapeutic materials can be regenerated, replaced or replenished after each harvesting with minimal damage to the environment. The underlying aim of SM is to use a holistic approach in animal healthcare in order to attain results in treatment that will eventually minimise or rule out further occurrences of diseases.

4. Infectious, non-infectious and metabolic diseases

Infectious diseases

• Caused by various infectious agents such as bacteria, fungi, protozoa and viruses, resulting in a fever reaction, which is the body’s defensive reaction to try and kill the infectious organism.
• Infectious diseases are contracted by coming into contact with infected animals or objects that have been contaminated with the infectious organism, while others can be transmitted by insects and ticks.

Non-infectious diseases

• Are not caused by infectious agents and they cannot be transmitted between animals. There are various causes and risk factors:
• Environmental causes – Non-infectious diseases can be caused by the interaction between the animal and its environment. Environmental causes include injury (cuts or broken bones), sun damage (cancer), drowning, lightning strike, heat stroke, burns and exposure to the cold.
• Parasites – Parasites are a serious threat to farm animals in South Africa.
  External and internal parasites cause a loss of production and deaths.
• Poisons – Animals that ingest poisonous substances may die or suffer severe organ damage which can affect their productivity. These substances include chemicals and poisonous plants.
• Genetic or congenital problems – These are conditions which the animal is born with. These are not always life threatening but some of them can be fatal.

Metabolic diseases

• Occur in farm animals due to an increased need for a nutrient. For example, a calcium deficiency in highly productive dairy cows causes milk fever. The animals show nervous symptoms and they may die if they are untreated.

The insects, etc. that transmit infectious diseases are called vectors.

Level of severity of animal disease
Level of seriousness of diseases, the speed with which they develop and their duration or course helps in making a diagnosis.

• Per-acute disease: develops very rapidly, is very severe and possibly fatal.
• Acute disease: it is severe and develops rapidly.
• Chronic disease: it develops slowly over a period of time and may be fatal if it remains untreated.
• Subclinical: this is when a disease-causing organism is present but the animal is asymptomatic. Clinical or visible signs may have passed or they may be seen later in the animal’s life.

Animal Diseases

1.Main micro-organisms causing diseases in animals
Infectious diseases are caused by infectious agents or microorganisms, including viruses, bacteria, protozoa and fungi, resulting in the four main types of diseases: viral, bacterial, protozoan and fungal.

Viral diseases
Viruses cause viral diseases. A virus is an infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host. There are six important viral diseases that occur in South Africa. They can spread very quickly, and are not treatable.

Foot-and-mouth disease (FMD): It is the most important threat to food security in a country because it affects the production of animals and it limits the export of agricultural products to developed countries. It is a state controlled disease.

Host

• FMD is a viral disease of cloven-hoofed animals such as cattle, sheep, goats, pigs and some antelope species.
• Transmission
• The FMD virus is very infectious. It can spread rapidly by direct transmission from animal to animal and by infected objects.
• It can also be spread by indirect transmission from one farm to another by infected animals or by trucks, clothes and instruments.
• Some animals become sub-clinical carriers of the disease when they recover.
• Symptoms
• Cattle develop blisters on their tongue and the mucous membranes of their mouth and feet. These can rupture and cause painful sores.
• They salivate and are unable to eat.
• Dairy cows develop blisters on their teats which allow mastitis-causing bacteria to enter and severely affects milk production.
• Sheep and goats develop less severe symptoms, and lesions are often unnoticed by the stock owner.
• Pigs in commercial systems are severely affected and they lose a lot of weight.
• Treatment and control
• There is no treatment for the disease. The state veterinary department controls FMD by fencing the South African borders and the Kruger National Park , where the buffalo are carriers of FMD.
• They also control animal movement during outbreaks by imposing quarantines and testing and slaughtering infected animals.

Rabies: This is an important animal disease because it can spread to humans and it is almost always fatal. It is a controlled disease.

• Host
• Rabies is a viral disease that can occur in all warm-blooded animals, including humans.
• Transmission
• It is transmitted through bites although sometimes it can be transmitted by saliva alone. The source of the virus varies in different parts of South Africa.
• Cattle are the most commonly affected livestock species.
• They become infected when bitten by infected mongooses or jackals.
• The virus has become established in domestic dogs in KwaZulu-Natal and the
• Eastern Cape which poses a danger to humans and other dogs.
• Symptoms
• The virus moves to the nearest nerve and then travels up to the brain.
• It can take up to a month for the first symptoms to develop.
• The same symptoms are evident in all animal species, namely a change of behaviour which usually leads to sudden bouts of aggression.
• Treatment and control
• There is no treatment for rabies in domestic animals.
• Cattle in areas affected by rabies can be vaccinated against the disease.
• All cats and dogs should be vaccinated regularly against rabies to prevent the exposure of humans to the disease.

Rift Valley fever (RVF): Outbreaks occur periodically as epidemics because the occurrence of RVF is affected by summer rainfall.

• Host
• Affects domestic ruminants but humans can become infected when they handle infected animal tissue.
• Transmission
• It is transmitted by mosquito species which prefer to bite livestock.
• Outbreaks usually occur in late summer and autumn.
• It is particularly common after heavy spring rains because this allows large numbers of mosquitoes to breed.
• Symptoms
• When an animal is infected by a mosquito bite, the virus is transmitted through the blood to the liver which becomes infected.
• The liver of an unborn foetus will be destroyed and it will die and be aborted
• During RVF outbreaks, 80–100% of pregnant animals abort if they have not been vaccinated. Large numbers of newborn and young lambs (most commonly affected), kids and calves die.
• Treatment and control
• There is no treatment. The control of the mosquito vectors is impractical in livestock. Annual vaccination with a live RVF vaccine before the late summer will protect animals from infections.

Avian/bird flu: This disease has become important worldwide because of its ability to mutate. This enables it to cause epidemics in humans. It is a controlled disease.

• Host
• Avian flu is caused by an influenza virus which is adapted to birds. But it can spread to other species, including humans, under certain conditions.
• Transmission
• Wild birds and ostriches can serve as asymptomatic carriers of the virus and they can spread the disease to commercial poultry farms.
• The virus is transmitted by direct contact with infected birds or indirect contact with contaminated objects.
• Symptoms
• In poultry the virus causes a wide range of symptoms including depression, breathing problems, a fall in egg production and sudden deaths.
• Treatment and control
• There is no treatment for avian flu.
• Infected birds like ostriches are slaughtered to eradicate the virus because of concerns about the potential spread to humans.
• Vaccines can be used in poultry houses to prevent the rapid spread of the virus.

African swine fever (ASF): Is a tick-borne viral disease which is confined to the African continent. It should not be confused with swine flu and European swine fever (or hog cholera) which do not occur in domestic or wild pigs in South Africa at present. ASF is a controlled disease.

• Host
• The ASF virus occurs asymptomatically in warthogs and bush pigs. It causes disease symptoms in domestic pigs.
• Transmission
• The virus is carried by a tampan which occurs in the burrows of warthogs and bush pigs in the northern areas of the country (Limpopo).
• Domestic pigs will develop ASF if they are bitten by an infected tampan.
• Symptoms
• The first signs of ASF infection in domestic pigs are high temperature, loss of appetite, listlessness and unsteadiness.
• Later on infected pigs can have bluish mucous membranes and exhibit breathing difficulties, vomiting and diarrhoea. They often die within four days after the first symptoms appear.
• Treatment and control
• There is no treatment or vaccine for ASF. So it is controlled by the state to prevent the spread of the disease from the limited area in the north of the country (Limpopo Province) where it often occurs. Veterinary services restrict the movement of wild pigs or their meat from Limpopo Province into other areas. Piggeries in this area are built according to certain specifications to avoid contact with wild pig species.

Newcastle disease (NCD): One of the most important diseases affecting the productivity of commercial and small-scale poultry. It is a controlled disease.

• Host
• NCD is an acute viral disease of domestic poultry. It also affects some other bird species such as waterfowl, pigeons and imported parrots.
• Transmission
• Transmitted when infected birds shed the virus through droplets that are spread when they cough, as well as through their faeces and eggs.
• Birds can be infected when they breathe in the virus or take it in by mouth
• The virus can be carried into poultry houses or onto properties when people handle sick birds or visit infected farms.
• The virus can be carried on people’s hands, clothes and shoes or on equipment.
• Symptoms
• Signs of the disease appear within five days.
• The virus can affect the respiratory, digestive and nervous systems.
  These systems can be affected in combination or in sequence.
  → The respiratory signs are gasping, coughing, sneezing and noisy breathing.
  → Nervous system signs include trembling, paralysis of the wings and legs, and twisting of the neck. Watery, greenish diarrhoea indicates that the digestive system has been affected.
  → Other typical symptoms are a severe decrease in egg production and the appearance of abnormal-looking eggs.
• Treatment and control
• There is no treatment for NCD. Birds in small-scale systems and commercial houses must be vaccinated because the disease affects egg production and weight gain.
• Several NCD vaccines are available.
• The B1 and La Sota strains are used commonly to vaccinate day-old chicks.
  These vaccines are given in their drinking water or sprayed in bird houses.

Bacterial diseases
Anthrax: A serious disease caused by the bacterium Bacillus anthracis. It is a controlled disease.

• Host
• Ruminants, pigs, horses, various wild animal species and humans.
• Transmission
• Farm animals become infected by direct contact with sick animals or by exposure to Bacillus anthracis bacterial spores in the soil. Spores are on the carcasses of dead animals which have died from the disease and been buried.
• Outbreaks usually begin when the anthrax spores are exposed by droughts or floods. The disease spreads rapidly when the carcasses are opened by scavengers or cut up by farmers. The infection may then spread to other species.
• Symptoms
• The disease is usually per-acute in ruminants. The animals commonly show very few symptoms and die rapidly. Anthrax should always be suspected in cases of acute death. Carcasses must not be opened until an animal health technician or veterinarian has made a blood smear. Brick-like anthrax bacteria are seen in the blood in positive cases.
• They may show a leakage of blood from body openings such as the nose and anus after death.
• Pigs may have a swollen throat and die more slowly.
• Treatment and control
• Treat animals with a high temperature with penicillin.
• The farm must be quarantined if an anthrax outbreak is suspected to control its spread. The quarantine lasts until 14 days after the last confirmed case of the disease.
• Carcasses must be buried and covered with lime to help break down the bacterium.
• All farms must vaccinate their animals every year to prevent an anthrax outbreak since it is impossible to eliminate anthrax spores from the soil.

Mastitis: An infection of the udder that usually occurs during lactation.

• Host
• Caused by various species of bacteria that infect cattle, sheep or goats. It is most important in dairy animals as it causes a loss of production.
• Transmission
• The bacteria are usually transmitted by contact with infected animals, either by milkers on the hands or milking machines.
• Infected cows serve as carriers of certain bacteria for healthy cows.
• The udders of cows can be infected by some environmental or soil bacteria, especially under muddy conditions.
• Symptoms
• There are different severities of mastitis and they range from per-acute to chronic cases. Chronic mastitis is usually only detected by somatic cell counts or cow-side tests like the California Mastitis Test.
• In very severe cases the udder can become swollen and inflamed. It eventually turns blue and gangrenous and animals may die because of toxin production by the bacteria.
• Acute and sub-acute cases show clots in the milk and painful swelling of the infected quart.
• Treatment and control
• Mastitis can be treated with antibiotics which are injected into the udder (intra-mammary preparations).
• Cows with badly damaged udders must be culled. There are many management practices to prevent mastitis in dairies and these include hygiene and the proper use of milking machines.

Tuberculosis: Bovine tuberculosis (or BTB) is a chronic disease of cattle and it causes a severe drop in milk production in cows. It is a controlled disease.

• Host
• Cattle are the main hosts of BTB although it can also infect humans.
• Transmission
• Mycobacterium bovis is the bacterium which causes BTB. It is transmitted directly by infected cows or indirectly on grazing or by equipment.
• Symptoms
• BTB is a chronic disease that develops very slowly. The first symptoms only become visible a few years after infection by which time the animal is sick.
• The bacteria cause the formation of small nodules in the lungs and other organs. Once the infection is widespread, the animal shows severe weight loss, swollen lymph nodes and it may develop a cough if the lungs are affected. Milk production of infected cows drops dramatically. Infected animals will die eventually.
• Treatment and control
• Antibiotic treatment of BTB is not economical.
• BTB cases must be reported to the state veterinary authorities who brand the animal with a T and supervise the slaughter in a special abattoir.
• All other cattle in the herd must be tested to identify infected animals. Cattle farmers must test animals for BTB before they buy them.

Protozoan or blood-borne diseases
Redwater: Caused by Babesia bovis and Babesia bigemina.

• Host
• The redwater parasite causes this disease in cattle.
• Transmission
• The protozoal organisms are transmitted by certain tick species which occur mainly in the northern and eastern parts of South Africa.
• Symptoms
• The two Babesia species cause similar symptoms initially. The Babesia parasites travel to the liver when cattle are bitten by infected ticks.
• The parasites spread to the red blood cells where they attach and multiply, and cause a fever.
• They eventually break down the red blood cells which causes anaemia and red discolouration of the urine (redwater).
• Animals become weak, stop eating and die within a short time unless they are treated.
• Nervous symptoms develop later with Babesia bovis. A cerebral or brain infection can give rise to increased excitability, convulsions and paralysis.
• Treatment and control
• Can be treated with babesicides. Calves can be vaccinated to control the disease. Exposure to infected ticks will also stimulate their immunity.

Anaplasmosis or gallsickness (Anaplasma marginale): Affects the red blood cells very chronically.

• Host
• It occurs in cattle.
• Transmission
• It is caused by the organism Anaplasma marginale. It is transmitted by ticks and attacks the red blood cells.
• Symptoms
• Animals develop a fever for a short time after being bitten by an infected tick
• Thereafter they gradually lose their appetite and their condition deteriorates
• They develop jaundice as their red blood cells begin to break down
• Eventually the rumen stops functioning due to lack of food and the animals become very weak.
• Treatment and control
• Can be treated with a dose of tetracyclines.
• Farmers may have to treat animals in chronic cases to get the rumen functional again.
• Calves can be vaccinated against anaplasmosis to prevent infection and their continual exposure to infected ticks will stimulate their immunity.

Heartwater: A very important tick-borne disease because it is fatal if untreated.

• Host
• This is a disease of cattle and small ruminants caused by Erlichia (Cowdria) ruminantium, which is a rickettsia or type of bacterial disease.
• Transmission
• Transmitted by the bont tick (Amblyomma hebraeum) which occurs in the eastern and northern areas of South Africa.
• Symptoms
• Animals that have been bitten by an infected tick develop a very high temperature, lose their appetite and later begin to show various symptoms as a result of damage to blood vessels.
• Fluid can build up in the brain which causes nervous symptoms such as high stepping, walking in circles and then lying down and paddling of the legs
• Fluid collects in the lungs and makes it difficult to breathe.
• Froth may be seen from the nose and the animals will die at this stage if they are not treated.
• Treatment and control
• Treatment with tetracyclines can save sick animals.
• Calves can be vaccinated against heartwater and this will protect them until adulthood.
• Adult cattle will be immunised by their continual exposure to infected ticks
• Sheep and goats must be dipped to prevent heartwater.

Coccidiosis: A protozoan disease that occurs in young ruminants and poultry. It occurs especially when animals are kept in crowded conditions. There are a large number of species of the coccidian parasite, such as Isospora and Eimeria.

• Host
• The condition occurs in young calves, sheep and goats up to the age of 2–3 months, and in poultry in intensive systems. Older animals become immune to the disease but they remain carriers.
• Transmission
• Coccidia infect the intestinal wall of their hosts. They multiply and produce oocytes which are shed in the faeces. These oocytes land on pastures or floors of poultry houses where they are picked up by susceptible animals.
• Symptoms
• The most typical symptom of coccidiosis in ruminants is diarrhoea. It can be mild or very severe and sometimes even bloody. Symptoms in birds are poor growth, depression and diarrhoea. A large number of deaths can occur.
• Treatment and control
• Anti-coccidials are given in the water or by injection to treat coccidiosis.
• Drugs called coccidiostats are used to reduce the number of organisms in the herd/flock.
• Vaccines are also available to control coccidiosis on intensive poultry farms
• Various management factors (e.g. improved hygiene, reducing crowding and stress factors) can be used to control the disease.

Fungal diseases
Lumpy wool: Caused by a fungus-like bacterium or actinomycete called

• Dermatophilus congolensis.
• Host
• This condition is seen in sheep as a result of continual wetting of the fleece.
• Transmission
• The spores of the organism are spread from one sheep to another. This occurs when the fleece remains wet from heavy rain or when sheep are dipped during cool weather.
• Symptoms
• The organism infects the skin and causes matting of the fleece or so-called lumpy wool. This damages and reduces the value of the fleece. It causes loss of condition in non-woolled sheep like dorpers.
• Treatment and control
• Antibiotics can be used to treat badly infected animals. Farmers should also prevent prolonged wetting of fleece and the contact of these sheep with unaffected ones.

Ringworm: An infection caused by a skin fungus. It is commonly caused by the fungus Trichophyton spp.

• Host
• It is seen in various domestic animal species but it is most common in young calves and Karakul sheep.
• Transmission
• Commonly found in young animals that are kept in unhygienic housing or poor conditions.
• The fungus is easily transmitted because it forms resistant spores which can be transmitted to other animals by direct contact or by indirect contact with infected pens or kraals.
• Symptoms
• The fungus infects the hair follicle and causes the hair to break off.
• Circular, hairless patches are usually seen and they are not itchy
• These patches usually appear on the head and neck but they can extend over the whole body.
• The condition is unsightly and reflects the poor condition of an animal.
• Treatment and control
• Apply iodine or sulphur preparations once a week to treat cases of ringworm.

2. Economic implications of animal disease
Death or mortalities
A high mortality rate can cause the farmer huge economic losses. Anthrax is an example of a disease that causes a large number
of mortalities.

Economic loss
Diseases that do not cause a high percentage of mortalities may cause economic loss because of a decrease in production. In these cases animals lose weight, show a drop in milk or egg production, fail to reproduce or suffer abortions.

Trade restrictions (export)
Some diseases cause huge economic losses because exports to countries that are free of those specific diseases are stopped.

Impact of animal diseases on the environment
Impact comes mainly from the methods used to prevent and control the diseases:

• Chemical substances, such as pesticides, can have direct effects on the environment by affecting unintended target organisms and animals, thus disturbing the functioning of ecosystems.
• Reduction of livestock morbidity and mortality promotes an increase in human and animal populations. Consequently pressure on the environment is increased, which puts resources at risk.

3. Prevention and control of animal diseases
It is very important to prevent and control animal diseases in South Africa because:

• viral diseases cannot be treated economically
• some bacterial infections cannot be treated, e.g. bovine tuberculosis (BTB)
• diseased animals suffer a loss of production
• treatment is often too late for some acute diseases
• some animal diseases are transmissible to humans (this is called zoonosis).

There are various methods to prevent and control diseases.

Vaccination

• This is one of the most important means of disease control. It is a simple intervention which is harmless to the animal and it can be used to prevent disease. This means that there is no production loss and the cost is very low when compared to the value of the animal.

Testing

• Some diseases are controlled by testing animals before they are purchased. The intra-dermal or skin test is a convenient method to identify TB infected herds.

Maintaining closed herds

• To prevent diseases such as tuberculosis, a closed herd is maintained. Only clean animals are kept and all new animals are tested before they are introduced to the herd. Fences must be maintained so that the herd is not exposed to infected animals.

Fencing, buffering and inspection

• This method can be illustrated by the example of a foot-and-mouth disease outbreak in the Kruger National Park. Animals are vaccinated in a buffer zone around the park. Disease transmission is monitored by maintaining fencing and frequently inspecting animals to monitor the possible spread of disease.

Quarantine

• It is very important to quarantine or isolate new animals before they are mixed with the other animals on a farm.

Parasites in farm animals

1. Parasites
Parasites of domestic animals are macroscopic creatures which spend part or all of their life cycle in or on the animal. They are important because they cause damage, transmit disease and sometimes even cause the death of the animal.

2. Internal parasites/endoparasites
These parasites that we refer to as worms. Most of these are found in the digestive system. Some internal parasites (e.g. tapeworms) have a temporary or intermediate host and a main host.

Roundworms

• Life cycle
• Large numbers of roundworms can occur in the intestines of domestic animals. They either absorb the food that is digested by the animal or suck blood from the intestine wall.
• After mating the female sheds eggs in the faeces of the host animal. The eggs land on grass pastures and they hatch under the right conditions. The larvae are picked up by passing animals.
• Animal hosts
• All farm animals have specific roundworm species which can infest them. Some of them cause severe loss of condition and production and even cause death in their hosts.
• Symptoms
• The symptoms of a roundworm infestation depend on the type of worm and these are shown in the table on pagepage 101. Infestation with certain roundworm species can severely affect the health and production of animals.
• Treatment
• Roundworm infestations can be diagnosed based on the observed symptoms. This can be confirmed by the presence of worm eggs in the faeces. Worm infestations can be treated with worm remedies.

Tapeworms

• Life cycle
• Adult tapeworms are long, flattened worms which occur in the intestine of their main hosts. They produce eggs when they mate and these are shed in the faeces. These eggs are ingested by the intermediate host and they form immature larvae or cysts.
• These resting forms of tapeworms remain in the tissues until they are eaten by the main host. The cyst then hatches in the intestine of the main host and the adult worm develops inside its intestine.
  
• Animal hosts
• All farm animals have tapeworm species which can infest them.
• Some of these species can cause health problems while others are more important for human health.
• Symptoms
• The milk tapeworm (Moniezia) can grow to a massive size and it causes a loss of condition in calves and lambs.
• The animals become stunted and pot-bellied and they may even die due to poor condition.
• Two other important tapeworms that aff ect animal health are the beef (Taenia saginata) and pork (Taenia solium) tapeworms.
• Their main host is the human being.
• When infected humans defecate on pastures, the tapeworm eggs are eaten by cattle or pigs and cysts develop in the muscles of these animals.
• Humans become infested with the tapeworm when they eat this meat.
• Treatment
• Young animals can be dosed with tapeworm remedies as soon as they begin grazing. (See also the table on page 101.)

Liver flukes (trematodes)

• Life cycle
• Farm animals may become infested when they graze in vleis or around dams where small water snails are found. These snails are the intermediate fl uke hosts. The snails shed the small, immature form of the fl uke (cercariae) onto the pasture and these are eaten by animals. Once in the intestine of the host, the cercariae develop into young fl ukes which then travel to the liver. They grow into adults in the liver where they suck blood and cause tissue damage.
  The females lay eggs which are passed out into the faeces and these eggs hatch into miracidia which infest the water snails.
• Animal hosts
• Cattle, sheep, goats and horses may become infested with liver fl ukes.
• Symptoms
• Liver flukes are bloodsuckers which cause severe anaemia and liver damage.
  Sheep can develop bloody diarrhoea.
• Treatment
• There are a number of remedies which can be used to treat liver fl uke infestation. (See next page.)
  

Financial implications of internal parasites
Roundworms, tapeworms and fl ukes can all cause loss of condition, poor production and even death in farm animals. The beef and pork tapeworm cause cysts in the meat which are referred to as measles. They cause losses for the farmer because this meat is condemned at the abattoir.

Preventative/control measures for internal parasites
Roundworm control programmes should be used to prevent heavy infestations. Select the correct remedy for the specifi c roundworm that needs to be controlled. Human tapeworm infestation of meat can be controlled if toilets are provided to prevent faecal contamination of pastures. Liver fl uke infestations can be controlled with remedies called fl ukicides, like closantel, clorsulon, rafoxanide and triclabendazole.

3. External parasites/ectoparasites
These include insects and arachnids. The insects have six legs and they include fl ies and lice. Arachnids have eight legs and this group includes ticks and mites. Most of these parasites feed on the blood, secretions or tissues of the host animal.

Flies: This category of external parasites includes two species of fl ies which cause problems in small stock.

• Blowflies
• Large, metallic green or blue flies which lay their eggs on animal carcasses. Some blowflies lay their larvae on live animals. A number of blowfly species (Lucilia cuprina, Chrysomya spp) lay their eggs on woolled sheep (merinos) in areas where the fleece becomes wet or soiled by urine or faeces.
• When the larvae hatch, they begin to feed on the softened skin and cause large wounds.
• Nasal flies
• Nasal flies (Oestrus ovis) are seldom seen by farmers because they fly very fast. They lay live larvae in the form of a maggot around the nostrils of sheep and goats. These larvae crawl into the nose and up into the nasal sinuses.
  They feed in the sinus area and they are sneezed out when they are mature.
  They then pupate in the soil and develop into adult flies.
• Nasal flies cause severe irritation to the infested animal which may lose weight or even stop eating.

Lice: Wingless insects that are related to flies.

• They spend most of their life cycle on other animals.
• Usually each domestic animal species is infested by a particular louse species.
• Red or biting lice irritate and damage the fleece or hair of woolled sheep and Angora goats.
• The infested animals then rub themselves against objects and pluck at their fleece. Blue lice suck blood and cause anaemia.

Ticks: Eight-legged insects that suck blood from animals.

• There are three stages of their life cycle, namely larvae that hatch from eggs laid by females, nymphae and adults.
• Ticks feed on the blood of animals at all of these stages.
• There are three different types of ticks.
• Ssingle host ticks: These ticks feed on the same animal at every stage throughout their lifecycle. The blue tick (Boophilus spp) is an example of a single host tick.
• Two host ticks: The larvae and nymphae of these ticks feed on small mammals. The adult ticks feed on domestic animals. The paralysis tick (Ixodes rubicundis) is an example of a two host tick.
• Three host ticks: The larvae, nymphae and adults each feed on different animals during their lifecycle. The hosts include wild animals, birds and domestic animals. The bont tick (Amblyomma hebraeum) is an example of a three host tick. These ticks are more difficult to control because they feed on different hosts and some of these hosts are wild animals.

Examples of important ticks in farm animals

Mites

• Closely related to ticks but they are much smaller, so most mites can only be seen with a microscope.
• Each domestic animal species is infested by a particular mite species which lives permanently on its body.
• Like ticks, mites have larvae, nymphae and adult stages to their life cycle.
  Mites burrow into the skin at all three of these stages and they feed on the serum which oozes from the wound.
• Psorgates ovis is one of the most important mites that affect farming and it causes a condition called sheep scab.

Financial implications of external parasites
External parasites cause damage to animals in various ways which can cause financial losses for farmers.

Damage to fleece in woolled sheep

• Blowfly strike in sheep causes losses in woolled sheep because it reduces the amount of fleece available to be sheared.
• Some parasites irritate the skin.
• Red louse infestation and sheep scab causes fleece to be plucked out, soiled or damaged when sheep bite themselves or scrape against objects like fences.

Loss of weight

• Certain ticks release substances which cause a loss of appetite in cattle. The cattle lose weight which leads to financial loss. External parasites which cause irritation of the animal like sheep scab, sheep louse infestation and nasal worm all cause loss of condition in the host animals because of this discomfort.

Weakness due to anaemia

• Heavy infestations with external parasites like ticks and lice that suck blood can cause anaemia, especially in young animals. The anaemia causes weakness and sometimes can even result in the death of animals.

Disease and death

• Some ticks carry the blood parasites that cause heartwater, redwater and anaplasmosis. These diseases cause serious symptoms which have to be treated and they require the farmer to spend money on medicines. If the animals are treated too late, the disease may result in the deaths of large numbers of animals.

Treatment and control of external parasites
There are various remedies which can be used to treat external parasite infestation.
Some of these can be used to prevent parasite infestations.

Flies

• Blowflies
• Wounds infested by blowfly maggots must be treated with products that contain insecticides. You can prevent blowfly infestations in woolled sheep if you spray them with remedies registered to control fly strike. It can also be prevented if you shear sheep around their hindquarters to prevent soiling with faeces.
• Nasal flies
• Sheep and goats with nasal worm infestation can be treated with an injection of macrocyclic lactones. They can also be dosed with other remedies registered for nasal worm control.

Lice

• Registered chemicals can be used to treat louse infestations.
• Clean herds can be maintained if you treat introduced animals before they have contact with the rest of the flock/herd.

Ticks

• Apply registered tick remedies to control ticks. They can be applied by dipping, spraying, pour-ons or tick grease. There are two main forms of control.
• Total or intensive control requires that all ticks are killed, such as in the case of dairy animals.
• Low level control allows a small number of ticks to survive so they can immunise animals against the tick-borne diseases that occur in the area.

Mites

• Mites cause a controlled disease called sheep scab.
• All flocks must be treated once a year with registered products as a preventative measure.
• The law states that all animals must be dipped or injected with registered remedies if an outbreak occurs.
• There are various remedies which are registered to control sheep scab, such as macrocyclic lactone injections and dips that contain amitraz or organophosphates.

Plant and metallic salt poisoning

1. Plant poisoning
The most important poisonous plants

Lantana (Lantana camara)

• Has spread over large areas of the country
• Is a declared weed in South Africa.
• Landowners must eradicate it, as it is an important cause of poisoning in cattle.
  Lantana causes irreversible liver damage.

Gifblaar (Dichaepetalum cymosum)

• A small herb that occurs in Limpop  and Gauteng and emerges in spring before other plants.
• Cattle may be tempted to eat gifblaar if there is nothing else to graze on.
• It causes heart failure which is untreatable.
• Gifblaar veld must be avoided in the spring.

Poison bulb (tulip poisoning); includes the bulbs Homeria and Morea spp.

• The plants are found in the central and western areas of the country, and the Eastern Cape.
• Is one of the few plant poisonings that can be treated effectively with activated charcoal. Farmers should keep new animals away from heavily infested pastures to control poisoning
• Affects hungry animals and those that have been newly introduced to the plants
• Animals can die suddenly of a heart attack or they can become apathetic
• This apathy is shown by lowered heads, groaning and grinding of teeth. .

Maize fungus (Stenocarpella (Diplodea) maydis)

• Grows on maize cobs in winter in the maize areas of the north western Free State, Mpumalanga and KwaZulu-Natal, especially during cool and wet weather.
• This poisoning causes 2% of all the plant poisonings in cattle.
• It causes nervous symptoms, mainly high stepping and paralysis.
• Poisoning can cause stillbirths and neonatal deaths in calves.
• There is no treatment for maize fungus but animals can recover if they are removed from the source of poisoning.

Thorn apple (Datura stramonium)

• These large annual weeds are found mostly on disturbed land.
• They produce spiny or thorny seed capsules which release large numbers of small black seeds. The leaves of the plant are used for medicinal purposes but they are seldom eaten by livestock because of their unpleasant taste. The seeds are also poisonous. Sometimes they are harvested along with maize or hay and this can poison ruminants and horses.
• The alkaloid in the seeds can suppress the heart rate, cause nervous symptoms and even death. The effect depends on the dose.

Prevention and treatment of plant poisoning
Most plant poisonings in animals cannot be treated. They usually cause irreversible damage to the body’s organs. Stock owners can prevent plant poisoning if they:

• learn about the plants in the area
• fence plants off during danger periods
• herd animals away from dangerous plants
• avoid overgrazing and overstocking.

2. Poisoning by metallic salts
Farm animals are exposed to chemical poisoning from various sources.

Metal salt poisoning

• There are two examples that can affect farm animals.
• Pesticides and herbicides are used on farms for weed and pest control and they can poison livestock. Organophosphates are often involved and this is sometimes due to their incorrect application on animals.
• Farmers occasionally also dose animals with copper sulphate if they suspect a deficiency in this salt. Sheep are very prone to poisoning if they receive a copper sulphate overdose.
• Symptoms
• Most agricultural chemicals cause nervous symptoms (e.g. muscle tremors and excitement, ending in death of the animal. Sheep poisoned with copper sulphate may die rapidly and show severe and jaundice.
• Treatment
• There is no treatment for most pesticide, herbicide or copper sulphate poisoning.

Urea poisoning
Urea is commonly used as a non-protein nitrogen supplement in ruminants and it is usually given in the form of a block.

• It can lead to urea poisoning under certain circumstances.
  Symptoms
• Excess urea intake converts the urea to ammonia which causes alkalosis.
  Poisoned animals show bloating, nervous symptoms, and can die if not treated.
• Treatment
• Administer vinegar into the rumen or by mouth to treat alkalosis. This treatment will restore the pH to normal levels.
• Prevention and treatment of plant poisoning
  Most plant poisonings in animals cannot be treated. They usually cause irreversible damage to the body’s organs. Stock owners can prevent plant poisoning if they:
• learn about the plants in the area
• fence plants off during danger periods
• herd animals away from dangerous plants
• avoid overgrazing and overstocking.

Prevention and control of poisoning by metallic salts and inorganic substances All herbicides and pesticides that are used on farms must be locked away safely. They must also be handled carefully according to the manufacturer’s instructions.
Urea poisoning can be prevented if you feed the urea to ruminants gradually and without breaks in between. The recommended amount (1% of the total feed) should not be exceeded and the urea blocks should not be allowed to dissolve in water.

3. Principles to control animal diseases and parasites

• Implement regular vaccination programmes to control preventable diseases that occur in your area.
• Implement regular parasite control programmes for internal and external parasites that occur in your area.
• Request proof of freedom from important diseases such as brucellosis and TB for which testing can be done.
• Quarantine new animals and treat them for parasite infestations during this period.

4.The role of the state in animal protection
The state uses various means to safeguard the national herd in order to maintain food security.

Legislation

• Certain laws which can be implemented to stop the spread of animal diseases.
  These laws stem from the Animal Diseases Act 35 of 1984.
• It gives the state certain powers during disease outbreaks. For example:
• the state in South Africa controls certain exotic diseases as well as FMD, African swine fever, Newcastle disease, anthrax, rabies, BTB and sheep scab.
  These are called controlled diseases.
• Some diseases must be reported to state authorities and these are called notifiable diseases. Examples include:
• lumpy skin disease, Rift Valley fever and blue tongue.
• Another important law is the Stock Remedies Act 36 of 1947.
• It ensures that medication sold for animal use has been tested to ensure that is both safe and effective. The stock remedy can then be given a registration number (or G number).

Import controls

• The state controls the import of animals into the country to prevent the importation of exotic diseases. Certain tests have to be performed on animals before they are imported into the country to show that they are free of certain diseases.

Laboratory services

• State-funded laboratories assist South African farmers with the diagnosis of diseases.

Vaccine production

• Onderstepoort Biological Products produces vaccines for South African diseases such as blue tongue, horse sickness and heartwater. These vaccines are only available in South Africa.

Topic questions

• Answer the questions below. Check your answers afterwards and do corrections.
• Give yourself one hour.
• Marks: 100

1. Choose ONE answer below to complete this sentence: Various laboratory tests can be done on live animals to help make a diagnosis. For example, a faecal examination can be done to ________
   1.1 to look for parasites in blood cells
   1.2 check for antibodies
   1.3 test for signs of roundworm
   1.4 grow a culture for an infectious agent (2)
2. Angora goats can suffer from anaemia. (4)
   2.1 List FOUR possible causes.
   2.2 How would you eliminate each cause to make a diagnosis? (4)
3. There is an infectious disease that causes deaths in newborn animals.
   3.1 Name this disease. (1)
   3.2 How can these young animals be protected? (1)
4. FMD causes few mortalities in farm animals. Discuss why it is important to control this disease. (5)
5. Animal health is important in livestock production.
   5.1 Study and complete the table below. Write down the question number, the letter and your answer next to each letter. (3)

   Scientific name	Internal/external	Type of parasite	Effect on host animal
   Psorogates ovis	external	sheep scab mite	A
   Lucilia cuprina	B	blowfly	wounds in woolled sheep
   Fasciola hepatica	internal	C	anaemia

   5.2 There are TWO examples of metallic salt poisoning that can affect farm animals. Identify them. (2)
   5.3 What are they symptoms and treatment of urea poisoning? (3)

6. Name FOUR infectious diseases in this topic that are zoonoses or transmissible to humans. (4)
7. Describe the general behavioural changes shown by a sick farm animal. (4)
8. Give TWO examples of a chronic infectious disease. (2)
9. It is important for farmers to control viral diseases.
   9.1 Can antibiotics be used to treat viral diseases? (1)
   9.2 What is the main method of control for these diseases? (1)
10. List FIVE typical symptoms of heartwater. (5)
11. There are various types of internal parasites.
    11.1 Which TWO main types have intermediate hosts? (2 × 1 = 2)
    11.2 Give an example for each answer in (11.1). (2)
    11.3 Name the intermediate host of each answer in (11.2). (2)
12. Livestock is vulnerable to ticks.
    12.1 Outline the negative effects of ticks on farm animals. (4 × 2 = 8)
    12.2 List the infectious diseases transmitted by ticks. (3 × 1 = 3)
    12.3 Explain how ticks provide immunity against tick-borne diseases. (2)
13. List FOUR important infectious diseases of pigs that have occurred in South Africa. (4)
14. Indicate THREE main types of livestock affected by foot-and-mouth disease. (3)
15. Poisonous plants can affect animal production.
    15.1 Name a poisonous plant that can cause liver damage in ruminants. (1)
    15.2 Name TWO poisonous plants that cause heart attacks. (2)
    15.3 Which plant poisoning causes nervous symptoms? (1)
    15.4 How can plant poisonings be prevented in a herd? (1)
    15.5 Give an example of a dip which can cause fatal poisoning in animals when the correct dose is exceeded. (1)
16. Why is sheep scab control vital to the wool industry in South Africa? (2)
17. Name FOUR conditions/parasites which can damage the fleece of sheep. (4)
18. An external parasite lays live larvae on its host.
    18.1 Name this parasite. Give its scientific and common name. (2)
    18.2 What are the symptoms of this condition? (1)
19. Describe the steps one can take to prevent urea poisoning in livestock. (4)
20. Explain the differences between the terms:
    20.1 infection and infestation
    20.2 macroscopic and microscopic (2 × 2 = 4)
21. Explain the meaning of these terms:
    21.1 serology
    21.2 histology
    21.3 postmortem (3 × 2 = 6)
22. The sale of medication for farm animals is regulated by an Act.
    22.1 Name the Act. (1)
    22.2 Explain the purpose of the Act.