1. HEARTWATER
INTRODUCTION
This is a disease of cattle, sheep and goats common in Africa. It is a rickettsia disease caused by a micro-organism larger than a virus.
CAUSE AND TRANSMISSION
The rickettsia is an intracellular parasite transmitted by the bont tick. The tick can transmit the infection through its changing from larva to nymph to adult every time it comes in contact with a different host animal.
SYMPTOMS AND DIAGNOSIS
Symptoms develop after an incubation period of 2 – 3 weeks. In acute cases, there is first a rapid rise in temperature followed by loss of appetite, difficulty in breathing, muscular tremors and nervous signs shown by the continual movements of the limbs, head and ears, tongue and jaw. Sometimes convulsions occur with rigidity of the neck, followed by death. Indigenous cattle with a high natural resistance or immunity show only a passing fever. A section of the jugular vein or cerebellum of the brain should be sent to a veterinary laboratory for examination.
TREATMENT AND CONTROL
In all cases, treatment is effective only if started early. Large doses of tetracyclines are the best form of treatment. Cattle born in heartwater areas, i.e. the lowveld and parts of the middleveld, usually pick up the infection when less than a month old and develop an immunity. Elimination of the bont tick which carries the disease is the best method of control, and this is brought about by frequent dipping or spraying procedures – preferably at weekly intervals – and with an acaricide to which the tick has not become resistant.
2. MASTITIS
INTRODUCTION
This disease is a major problem in dairy herds. The term means inflammation of the udder. It can occur in almost all mammals but it is of major importance in cattle. It is of major economic importance because of pathological changes in the mammary gland which affect the quantity and quality of the secreted milk.
Mastitis is found all over the world and is also found amongst sheep, goats and buffaloes. In the developed dairy cattle industry, an average incidence of about 40% of animals affected with mastitis is not uncommon, with a comparable loss of productivity.
CAUSE AND TRANSMISSION
A number of species of micro-organisms have been associated with mastitis and they can be separated into two groups, i.e. those that are infective, and those that are potentially pathogenic. Their common characteristic is that they can be found in the environment of the animal, either in the dung, urine or bedding. Infection nearly always occurs by the micro-organism gaining access to the udder through the teat canal. Normally, the udder tissue and the milk within the udder and cistern are sterile. When one or more of a large number of predisposing factors are present, the micro-organisms are able to pass along the teat canal and so enter the udder, where they set up the infection. These factors include: age, high yielders, hereditary factors, trauma, hygiene and unknown factors.
SYMPTOMS AND DIAGNOSIS
The udder may swell. The way a cow walks may indicate pain. Before milking, the four quarters may be observed to be hanging unevenly. Examination of the teats may reveal injuries or sores especially near the orifice. There may be a rise in temperature and pulse rate. As the disease progresses, the affected tissue of the udder becomes hard. The milk yield decreases and the milk becomes thin, watery or grey in colour. The use of the strip-cup is strongly recommended as a means of giving the first indication of the presence of mastitis. A strip cup is a cup-shaped metal container of about 250ml capacity with a ledge about 3cm from the rim, on which a disc of fine gauze rests. The milk stream is directed onto the gauze for the milk to pass through and flakes and clots to be collected. In all cases where laboratory testing is to be carried out, the collection of a suitable milk sample is of the utmost importance. Contaminated samples are worthless. Samples should be sent to the laboratory in a vacuum flask with ice to keep the milk cool.
TREATMENT AND CONTROL
Antibiotics have proved to be the most useful therapeutic agents in the treatment of mastitis. The most convenient means of administration is by udder infusion via the teat canal. A broad-spectrum antibiotic can be used especially for those cases where continued use of penicillin has rendered it resistant. Preferably a combination of antibiotics may be used. Control can be affected by the accurate determination of the extent of the disease in the herd. This can be achieved by the careful and frequent use of tests, the use of the strip-cup and the accurate identification of the micro- organism which causes the disease. However, even with the most careful hygiene in the dairy, mastitis will sometimes persist. Hot water in a bucket with dairy disinfectant should be constantly at hand. A separate clean cloth should be used for each cow. No vaccine has yet been developed for use against mastitis, whatever the causal micro-organism.
3. SALMONELLA
INTRODUCTION
Salmonella is the name for a group of diseases which occur in almost all animal species and in birds. Organisms of the group are found all over the world, the most important in the Tropics are those occurring in cattle, pigs, sheep and poultry. They are all classified as paratyphoid organisms apart from two members of the group which only occur in poultry.
CAUSE AND TRANSMISSION
Stress is a pre-disposing element in most instances of salmonella, especially in adult animals. Salmonella have little resistance to sunlight, drying or heat, but can remain for at least 7 months in soil, water, faeces and pasture. Man is also
susceptible to this disease. Transmission occurs from contamination of water, pasture or feed. The carrier state exists and may continue for the life of the animal. Ingestion is the usual mode of entry, and infection depends on the number of micro-organisms and the susceptibility of the host, especially where stress occurs.
SYMPTOMS AND DIAGNOSIS
There are two major syndromes, i.e. the septicaemic and the enteric, the latter being either acute or chronic.
In the septicaemic syndrome, it is found to affect young animals often 10 – 14 days after birth: there is dullness, high fever, and the faeces are putty-coloured and contain blood streaks. Death may
occur 1 or 2 days after the onset of the symptoms, or it could occur between 5 – 7 days. A nervous syndrome may be seen in the form of tremor, paralysis and convulsions. Animals which have recovered may carry the infection and act as reservoirs into adult life.
The Enteric Syndrome is commonly seen in adults. First there is a fever which lasts for 12 – 24 hours followed by severe watery diarrhoea containing blood clots. Death can occur within 24 hours but more often up to 5 days from the appearance of the first symptoms. Recovered animals can become carriers for life. In dairy cattle there is a cessation of milk together with severe abdominal pain and marked emaciation. The diagnosis of salmonella is difficult and confusion may arise with massive fluke infestation. It is essential, therefore, to have the disease confirmed by sending samples to a Veterinary Laboratory for clinical diagnosis. The standard therapeutic dosage of drugs such as antibiotics and sulphadimidine is satisfactory. They may be administered orally.
TREATMENT AND CONTROL
Medication of drinking water has been found to be helpful. It must, however, be kept in mind that animals which recover may still excrete the micro-organisms and thus act as carriers. Vaccination is not very effective. Some immunity is produced but may give a misleading feeling of security. Good husbandry and good hygiene, careful testing before the purchase of replacement stock and frequent testing, particularly on suspect animals, may go a long way towards controlling this disease. Animals suspected of having the disease should be culled.
4. TETANUS
INTRODUCTION
This is an infectious bacterial disease affecting all animals and man. The bacteria form spores which can survive for many years and are very common in old cattle kraals.
CAUSE AND TRANSMISSION
The bacteria are straight rod-shaped anaerobes with rounded ends which form spores. These spores are highly resistant and able to withstand desiccation indefinitely, boiling for 1 hour and 5% phenol for 15 hours. They are quickly killed at 105°C, but the spores can survive in soil for many years. Infection takes place by contamination of wounds with the micro-organism. Castration of big calves by rubber rings provides an opportunity for tetanus infection. In wound infection, the toxin travels not via bloodstream, but via the peripheral nerve trunks to the brain, where it causes marked exaggeration of the response to normal minor stimuli, so that muscular tension is produced.
SYMPTOMS AND DIAGNOSIS
The incubation period is between 1 and 2 weeks, but in young animals it may be as short as 3 days. Or it may remain latent and many months may pass between contamination and the appearance of symptoms. There is first an increasing stiffness, the temperature is raised, the ears become stiff, and the jaw becomes rigid (lockjaw). The animal goes off its feed owing to the jaw muscles being in spasm. Fatal cases in large animals take from 5 – 10 days and in small animals, 3 – 5 days. Tetanus is difficult to confuse with any other disease.
TREATMENT AND CONTROL
In cattle, an anti-toxin is available and cleansing of the wound is also helpful. Muscular relaxation is achieved by the injection of relaxants. Proper hygiene at castration and other surgical procedures should always be observed. Nails and wire should not be allowed to lie around where animals are
reared. Short-term vaccination can be achieved by the injection of anti-toxin subcutaneously. Protection lasts for about 2 weeks. Active immunity can be obtained by the use of an effective toxoid. This can be obtained in most countries. Usually 2 or 3 injections are given in a fairly short period of time, and thereafter annual vaccination is valuable.
5. TUBERCULOSIS
INTRODUCTION
Bovine tuberculosis is a chronic disease which affects man as well as cattle and other mammals. It is a very ancient disease. Although now very nearly eliminated from many countries, it remains a very dangerous disease in some areas of the Tropics.
CAUSE AND TRANSMISSION
The disease can attack any organ in the body, but is most commonly found in the lungs (pulmonary form), intestines and udder. Beef herds on highland pastures are not generally affected but dairy herds grazing on low, wet land may suffer a higher incidence. There has been experience of transmission among humans equalling that of cattle. It is caused by the bacteria Mycobacterium bovis and a slender, rod-shaped micro-organism which has the specific characteristic of being acid- fast due to a waxy substance which prevents the absorption of the common dyes used in staining, and also renders it more resistant to external influences.
SYMPTOMS AND DIAGNOSIS
There are no clear-cut symptoms which indicate the presence of the disease. The main symptoms in the lung form are persistent coughs which last for some months, getting gradually worse. The sufferer loses condition.
Even though the disease may spread to one or more organs or be generalised through the whole body, no clinical sign may be found.
However, the animal may become emaciated. Recognition of the enlargement and induration of superficial lymph nodes is a time-honoured system of identification of the presence of tuberculosis. As there is a marked variation in symptoms it is sometimes impossible to identify the disease with certainty.
TREATMENT AND CONTROL
Suspected cases must be reported to the Department of Veterinary Services. There is a very effective allergy skin-test for the disease, and usually all dairy herds are tested this way. A sound system of control is by the elimination of reactor animals. There is no treatment for this disease in cattle and it is essential that efforts are directed towards the prevention of the spreading of the disease by strict isolation and hygiene.
6. VIBRIOSIS
INTRODUCTION
This is a contagious venereal disease of cattle. It is caused by vibrio foetus. The bacteria live in the uterus of cows where a mild inflammation is set up. The bacteria also live in the sheaths of bulls.
CAUSES AND TRANSMISSION
Transmission occurs during coitus, and infected bulls may carry the micro-organism indefinitely, as may mature cows. However, in some cases, it clears up spontaneously.
The micro-organism can survive the low temperatures used in semen storage for use in artificial insemination and this is known to be a potent means of spreading the disease.
SYMPTOMS AND DIAGNOSI
Often, at the beginning of an outbreak, the female herd shows infertility or the fertility rate is poor. After a few months, fertility rates improve, and while abortions may occur at any time during pregnancy, the abortion rate is generally low. The collection of mucous on a swab from the vagina of cows and heifers suspected of having the disease should be sent for laboratory examination.
TREATMENT AND CONTROL
Bulls may be treated with antibiotics in the form of penicillin or streptomycin cream. Bulls should be vaccinated twice, the first vaccination before the commencement of the bulling season and the second vaccination, one month before the bulling season. The rigid checking of bulls, whether they are used for artificial insemination or for natural service, is essential for effective control of the disease.