1. ACTINOMYCOSIS (Lumpy Jaw)
INTRODUCTION
This is a chronic infectious disease, mainly found in cattle. A typical symptom is an osteomyelitis of the bones of the head. The disease affects pigs and other animals sometimes, but rarely man. It occurs throughout the tropical regions of the world.
CAUSE AND TRANSMISSION
Infection is believed to occur through small wounds in the mouth caused by splinters of dry feed that travel through the blood or lymph vessels to internal organs. Infection may occur in young cattle by penetration of damaged buccal mucous membrane when the teeth are emerging. Aerial infection may be the cause of the lesions in the lung.
SYMPTOMS AND DIAGNOSIS
There is no accurately determined incubation period but it seems probable that it is many months. The first indication of the disease is a painless bony swelling which arises on the lower edge of the mandible or on the maxilla, which may not be noticed until it has reached a considerable size. It may become very large, hard and immovable for a few weeks, or it
may develop more slowly over many months. Often eruption occurs at one or more points on the surface of the skin with pus oozing out. The pus is of a sticky consistency, translucent in appearance and contains numerous small sulphur-like granules. These often heal over and break out afresh elsewhere on the lesion. The distortion of the bone and teeth make it difficult for the animal to masticate, so it therefore loses condition. In some cases, the condition becomes generalised. Abscesses in the jaw area caused by the penetration of certain types of grass seed are at first glance similar to those caused by actinobacillosis, but can be distinguished by the location of the primary lesion and confirmed by laboratory examination.
TREATMENT AND CONTROL
Local injections of antibiotics, when the lesion is circumscribed, can be effective provided they are started early on in the infection. Streptomycin, at the rate of 10 to 15mg per kg of the body weight daily for 3 or 4 days and repeated periodically, has been found to be effective. The removal of the lesion should be carried out where this is feasible. Any treatment with iodine preparations are of limited value unless the problem is discovered early. A combination of iodine and streptomycin therapy has been found to be more effective than either drug administered alone. Prompt treatment of affected animals is probably the only effective method of control. Isolation of affected animals and early slaughter are recommended.
2. ANAPLASMOSIS (Gall Sickness)
INTRODUCTION
This is a disease mainly affecting cattle but also affects sheep and goats and is characterised by jaundice, anaemia and debility. It is prevalent in most African countries, in Eastern Asia and Australia. It is often the cause of serious economic loss, not because of a high mortality rate but because of the debility displayed in infected animals.
CAUSE AND TRANSMISSION
The genus Anaplasma contains 3 main species. Anaplasma is similar to rickettsia in morphological appearance, having a small spherical body about 0.2 – 0.5 microns in diameter, staining red with
Giemsa. It is a tick-borne disease and many ticks have been found to carry the disease. Transmission occurs via the egg in some tick species. Mechanical transmission can also take place via biting flies, and similarly, the anaplasma can be carried on surgical instruments, i.e. castrating knives, syringe needles, etc. The carrier state also exists; carrier animals are a common source of new outbreaks and may remain infective for very long periods. Resistance appears to decrease with age. Wild animals probably act as reservoirs of infection, although the disease appears to be non-pathogenic in them.
SYMPTOMS AND DIAGNOSIS
Symptoms are anaemia and jaundice as the anaplasma attacks and destroys the red cells. The onset of symptoms occurs 3 to 4 weeks after the first infection and is accompanied by fever. Acutely infected animals die rapidly at this stage. In the survivors, the temperature fluctuates for 1 or 2 weeks. During the acute stage, animals tend to become aggressive and abortion is common. Recovery is slow and dependent upon the ability of the animal to build up a resistance to anaplasma. Anaemia and jaundice are apparent. The blood is thin and watery. Blood smears, blood serum and affected organs should be taken to the laboratory for examination. Diagnosis can only be confirmed by a positive complement fixation test and by successful transmission experiments. This is because babesiosis and trypanosmiasis are similar. There may also be confusion with leptospirosis and it is helpful if identification can be made of blood in the milk of infected animals. This is a condition which occurs in leptospirosis, but does not usually occur in anaplasmosis.
TREATMENT AND CONTROL
Broad spectrum antibiotics are useful in the treatment. Oxytetracycline (3-5mg/kg of body weight), or Chlortetracyline (5-10mg/kg) should be administered daily, or better still, 2 or even 3 times daily. They are more effective if given intravenously. Although the bacteria can be drastically reduced they are not entirely eliminated, and it should be noted that the anaplasma persist into the carrier state even with intensive treatment. The earlier treatment is commenced the better, but anaemia may still persist for some time. Blood transfusion helps in the treatment of valuable animals, but is not normally practical.
Complete eradication is not usually possible of the large number of ticks and other insects which may transmit the disease but much can be done to reduce the incidence. The control of ticks and other disease-carrying insects is helpful. Control is based on the establishment of a condition of pre- munity and to produce this there are 3 forms of vaccination. It is essential to see that a mild infection is observed in vaccinated animals (i.e. that the vaccine has taken).
3. ANTHRAX
INTRODUCTION
This is an acute, infectious, septicaemic disease which affects all animals, but especially cattle, sheep, goats, pigs, horses and man. Carnivores are more resistant. It is characterised by sudden death and there is a black tarry exudate from the nose and anus. The disease occurs world-wide but is more common in tropical than in temperate countries.
CAUSES AND TRANSMISSION
The Bacillus anthracis is a large rod-shaped, spore-forming micro-organism which occurs in vast numbers in the blood of an infected animal, and it can be seen readily under the microscope in stained blood smears. The spores are highly resistant to standard disinfectants. In suitable
environments, anthrax spores are believed to remain infective for 10 years in soil or pasture. A toxin released by the bacilli can cause oedema and damage to tissue resulting in death by secondary shock and acute kidney failure. Animals are usually infected by ingestion of material containing spores or active bacilli. Infected meat, bonemeal, hides, bones, hair, horns and hooves have all been traced as a source of further infection. These sources have introduced
the disease into new areas and different countries.
SYMPTOMS AND DIAGNOSIS
In cattle, the disease may be peracute or acute. The incubation period is probably 1 – 2 weeks. Usually, the animal will be ill for only a day before it dies. Sudden death of animals will be sufficient to suggest the presence of anthrax. Diagnosis may be made post mortem by laboratory examination of a blood smear. This must be taken as soon as possible after death. When anthrax is suspected after a carcass has been opened, a piece of spleen, liver or kidney should be taken and sent to the laboratory for confirmation.
TREATMENT AND CONTROL
Large doses of penicillin may assist, but usually the animal is dead before the disease is suspected. Where early diagnosis is possible, oxytetracyclene should be given at the rate of 4mg per kg of weight daily. Treatment should continue for at least 6 days. Strepomycin (5g intra-muscularly twice daily for cattle) is also effective. Other antibiotics are also good. Most countries have very stringent regulations regarding notification, isolation, disposal of carcasses and disinfection. Where the disease is suspected, the owner must notify the local Department of Veterinary Services. Known infected areas must be quarantined and all animals prevented from entering for at least 6 months after disinfection. Numerous vaccines are available and are effective. Vaccines take 2 weeks to produce immunity and must be repeated annually.
4. BLACKLEG (Quarter Evil)
INTRODUCTION
This is an acute, infectious but non-contagious disease. It is found most commonly in young cattle, 6 months to 2 years old. It may also be found in sheep and goats. It is widespread in tropical countries.
CAUSE AND TRANSMISSION
This disease is caused by gram-positive, spore-forming, rod-shaped, toxin producing anaerobe, the spores being highly resistant to heat and desiccation. These spores survive in the soil for many years. They enter the body by ingestion and absorption occurs via the mucous membrane of the alimentary tract. In sheep, the micro-organism enters the body via wounds such as those resulting from shearing, castration and docking injuries or injuries which damage the skin, e.g. fighting. Ewes may become infected during lambing through injuries to the vulva or vagina.
SYMPTOMS AND DIAGNOSIS
Cattle will develop a high fever, depression, loss of appetite and often a marked lameness with swelling of the upper part of one of the limbs. Progress of the disease is rapid, and death occurs from toxaemia 24 – 36 hours after the first appearance of fever. In sheep there is a high fever and loss of appetite and death occurs in 24 – 36 hours, as with cattle. In all cases, smears should be made and material aseptically collected from the lesion for laboratory examination. Additionally, samples of heart blood and heart muscle should be collected for laboratory examination.
A diagnosis can usually be made on the basis of the history and the clinical signs. The crepitation of lesions in cattle is an important sign. However, sudden death may be attributed to anthrax. Correct diagnosis is essential.
TREATMENT AND CONTROL
Good results can be obtained with antibiotics if there is early diagnosis and rapid treatment. Penicillin, chlortetracyclene and oxytetracyclene are all of value and should be given in normal dosage. Vaccination is not expensive and is recommended for use wherever possible. In sheep, vaccination prior to lambing or castration and docking is a useful precaution.
5. BRUCELLOSIS (Contagious Abortion)
INTRODUCTION
This is an infectious disease of cattle which causes abortion between the 6th and 8th month of pregnancy and can also cause infertility. It is widely known in most tropical countries.
CAUSES AND TRANSMISSION
The disease is caused by a small gram negative micro-organism which can be destroyed by common disinfectants and sunlight. However, it can survive several weeks in damp, shady places. It is killed in the pasteurisation of milk. The disease attacks breeding cows and heifers. Man is also susceptible. The introduction of the disease in a herd is usually by the introduction of an infected cow. Within the herd, cattle are mostly infected through ingestion of infected material, but it can also occur via the respiratory tract, the conjunctiva and broken or unbroken skin. Blood-sucking insects can transmit the disease, particularly ticks. However, there is no doubt that forage infected by an aborted foetus or membranes is the quickest means of spreading the disease. Man is infected by handling the rear end of an infected cow after she has aborted, and by drinking unpasteurised milk from an infected cow.
SYMPTOMS AND DIAGNOSIS
Cows can be seen trying to calve earlier than expected. The foetus will be small and often the after- birth is retained. In a susceptible herd, infection spreads rapidly and most of the cattle abort. They will then carry their subsequent calves to full term, but after calving, the incidence of retained placentae will be high.
Calves which become infected often rid themselves of the brucella bacteria, but sometimes they carry the brucella in the dormant state until they become sexually mature, when the infection re- occurs.
It is necessary to submit the foetus and a portion of the afterbirth to the Veterinary Research Laboratory. Blood samples for a Serum Agglutination Test requires about 20ml whole blood, or 10ml serum.
TREATMENT AND CONTROL
There is no effective treatment. Vaccination with S 19 Brucella vaccine should ideally be given routinely to heifer calves between 4 and 9 months of age. Hygiene is an important factor in the control of the disease. Infected foetuses and membranes must be located and then burned or sterilised. Great care must be taken to disinfect the area contaminated by aborted material. Infected animals must be isolated from those not infected. This also applies to pigs and horses coming onto a farm. They should be tested and kept in isolation. In all cases, reliable and frequent testing is necessary. If there is a likelihood of re-infection from outside the farm, calves should be vaccinated and infected animals culled.
6. FOOT ROT
INTRODUCTION
This is a common term applied to conditions of the feet. It affects cattle, sheep, goats and, sometimes, pigs. It is very widespread in the tropics as it is related to climate conditions and flourishes in high temperatures and humidity.
CAUSE AND TRANSMISSION
The germ which is an aerobic bacterium penetrates the hoof through any small wound. These can be caused by ticks, the larvae of nematodes or by standing on any sharp object. Animals in the chronic state transmit infection directly to healthy animals.
SYMPTOMS AND DIAGNOSIS
It is not difficult to diagnose foot rot. In all animals it manifests in acute lameness and there is a rise in temperature and a loss of weight. Dairy cattle show a drop in milk production. In cattle, the feet become swollen, the coronet becomes red and hot, the skin of the inter-digital space becomes cracked and swollen, eroded and often ulcerated. Generally more than one foot will be involved. Animals are often unable to stand. Animals in the advanced stages are best culled. The rapidity of the spread of the disease among a herd or flock is characteristic in specific outbreaks, when climatic conditions become favourable.
TREATMENT AND CONTROL
Antibiotics such as tetracyclines can be injected. Local treatment, i.e. the cleaning of the lesion and application of an antibiotic spray are also helpful. Putting cattle through a foot-bath containing a solution of 10% copper sulphate or 5% formalin, two or three times a week helps prevent the spread of the disease. Infected animals should be isolated, and a close watch kept on the rest of the herd. It is best if cattle can be made to stand in the footbath for 10 minutes. This means holding each group instead of allowing them to walk through the footbath at the normal pace.
