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Gallsickness in cattle

Written by  Dr Joan Kleynhans
| in Veearts
| November 3, 2014

Anaplasmosis in cattle was formerly known as gallsickness. It is caused by a bacteria, Anaplasma marginale, of the order Rickettsiales, which lives inside red blood cells (obligate intraerythrocytic).

It occurs in tropical and subtropical regions worldwide, including South Africa as far as 32 degrees South.

Transmission and epidemiology

        Boophilus tick species are the main vectors in South Africa. The tick will feed on an infected animal and then transmit the disease during the same or following stages of its life-cycle. Rarely the tick may transmit the disease via its eggs. Biting flies have also been shown to transmit the disease. If a pregnant cow is infected during the second or third trimester, the disease may be transmitted to the calf via the placenta. Contaminated needles or surgical equipment may also transmit anaplasmosis.
        Calves are much more resistant to disease than older cattle. This is inherent and is not due to colostral immunity.  In endemic areas losses due to anaplasmosis are minimal. Animals first become infected while young. Cattle remain chronically infected carriers after they recover from the acute phase of infection. As a rule, they are then immune to clinical disease, unless they are immunosuppressed, e.g. by administering corticosteroids, or are suffering from concurrent disease. When adult cattle with no previous exposure are introduced to an endemic area, significant losses may occur.

Clinical findings

        Severity of disease increases with age. Animals under a year rarely show symptoms. Between 1 and 2 years animals become moderately ill. In older cattle disease is severe and can be fatal.
        The destruction of red blood cells by the disease leads to progressive anaemia. The pre-patent period, from infection to the appearance of symptoms, depends on the infective dose and ranges from 15 to 36 days, although it can be as long as 100 days. Then peracute, acute or chronic anaplasmosis is seen. At the peak of infection between 10 and 20% of red blood cells are infected, though it may be as high as 65%.
        Peracute infection causes death within hours of first appearance of symptoms. In acute infection there is rapid loss of condition, fall in milk production, loss of appetite, incoordination, shortness of breath and a rapid bounding pulse. Brown urine may be seen, but is not due to haemoglobinuria as in Babesiosis. A transient fever up to 41⁰C occurs at the peak of infection. Pale mucous membrane becomes yellow as disease progresses. Pregnant cows may abort. Surviving cattle take weeks to recover fully.
        Bos indicus cattle seem to be more resistant to A marginale infection than B taurus. Varying resistance between individuals and virulence differences between strains and the level and duration of infection also plays a role in the severity of disease.

Post mortem

        Carcases are anaemic and jaundiced with thin, watery blood. The spleen is soft and enlarged and prominent follicles are visible. The liver has a mottled, yellow orange appearance. The gallbladder may be distended with thick brown or green bile. Lymph nodes in the mediastinum appear brown. Clear fluid is seen in the body cavities. Lung oedema, pinpoint bleedings on heart surfaces and gut stasis are evident. Microscopically many red blood cells are infected with A marginale. It is important to distinguish between Anaplasmosis and Babesiosis as both are transmitted by ticks and may cause similar symptoms.

Treatment

        Early treatment with tetracycline drugs or imidocarb will usually ensure survival. A single intramuscular injection, preferably into the neck muscle,  of a long-acting oxytetracycline at 20 mg/kg is often used. More severely affected cattle may need a blood transfusion to survive.
        Withholding periods must be observed for milk and meat.  Imidocarb is a suspected carcinogen with long withholding periods. It is not approved for use in the USA or Europe.

Prevention

        A live vaccine is available in South Africa. It contains A centrale, which confers partial immunity against disease caused by A marginale. A small number of cattle may have severe reactions to the vaccine. In some areas, stringent tick control may be a feasible way of preventing the disease.