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Babesiosis in cattle

Written by  Dr. Joan Kleynhans
| in Veearts
| June 2, 2015

Bovine babesiosis, known as redwater, is a tick-borne disease. It is a protozoan parasite which lives in red blood cells.

Two species are of economic importance in South Africa, namely Babesia bovis (Asiatic redwater) and Babesia bigemina (African redwater). European cattle breeds are more susceptible than Zebu or Sanga breeds.

Babesia bovis was probably introduced into Southern Africa with the Asian blue tick Boophilus microplus, in the late 19th century. It was first reported in South Africa in 1941. Babesia bigemina is predominantly transmitted by B. microplus and the indigenous blue tick, Boophilus decoloratus. It is also spread by Rhipicephalus evertsi evertsi. It is believed to have been endemic in Southern Africa for centuries.

“Of the two forms, B. bovis is more virulent.”

During the first part of the 20th century redwater was indirectly controlled by tick control measures aimed at controlling East Coast fever, spread by the tick Rhipicephalus appendiculatus. In the 2nd half of the 20th century tick control was relaxed. Boophilus spp also developed resistance against acaricides. In 1972 redwater caused the death of 10 000 cattle in the Eastern Cape. During the war in Zimbabwe a million cattle were lost due to redwater.

Of the two forms, B. bovis is more virulent. However, B. bigemina is widely distributed in the country and possibly more important.

The distribution of B. bovis is restricted by the distribution of its tick vector, B. microplus. This includes the Eastern Cape, KwaZulu-Natal, and Mpumalanga in South Africa. It also occurs in other Southern African countries. B. bigemina occurs throughout the subcontinent, except for the drier parts of the Western and Northern Cape and the western Free State, Namibia, Botswana and some high lying areas of the Drakensberg and Lesotho.

Calves born to immune mothers are resistant to the disease, but calves of unexposed cows, less than two months old, are susceptible to infection and become ill. Once calves pass the age of two months, they are protected by a natural innate resistance which lasts 4 to 6 months and is not dependent on the immune status of the cow. Most cattle develop a long-lasting immunity after recovery from the disease.

B.bovis and B.bigemina cause similar clinical signs, but the course of disease and its outcome are often different. Incubation in both vary between 8 and 15 days.

Babesia bovis

Fever of over 40 degrees Celsius is usually present for several days before other signs are seen. The first signs are inappetence (lack of appetite), depression, weakness and a reluctance to move. Blood is often present in the urine. Pale and yellow mucous membranes are seen, especially in more protracted cases. Cows may abort. As cases progress, muscle-wasting and tremors are seen and coma develops in terminal cases. Death may occur from one to several days after onset of signs. Cases that survive may take weeks to regain condition, but recover completely. Fertility of bulls may be reduced for 6 to 8 weeks.

In some cases, cerebral babesiosis develops. Affected animals show hypersensitivity to to touch, nystagmus, circling, head pressing, aggression, convulsions and paralysis. Affected animals die soon.

In sub-acute cases clinical signs are less pronounced. Calves infected before the age of 8 months may develop an unapparent form of the disease.

Babesia bigemina

Cattle are generally not as severely affected as in the case of B. bovis infection. However, the disease can develop very rapidly with sudden, severe anaemia and icterus, and can be rapidly fatal. Blood in the urine is seen earlier and more consistently than in B. bovis infections. Cerebral involvement is not seen. Non-fatal cases will recover quickly and completely.

“B. bigemina parasites are usually more numerous in a blood smear and easier to detect. “

Diagnosis is based on clinical signs and post mortem lesions. Blood smears are required to confirm the presence of Babesia. B. bigemina is a larger parasite than B. bovis, although there is variation and a microscope with a micrometer is useful to measure the organisms. B. bigemina parasites are usually more numerous in a blood smear and easier to detect. B. bovis may be hard to find. Thick blood films are useful to detect B. bovis. In thick films the blood is not spread over a large area and is not fixed before staining. This allows lysis of the red blood cells and concentration of the parasites. These smears should ideally be stained with a 5 to 10% Giemsa solution for 20 minutes. Smears should be clean, as dirt may mask the presence of parasites. If an animal has been treated, parasites will degenerate and disappear within 24 hours. Blood smears should also not be exposed to formalin or moisture.

Babesia parasites become rounded a few hours after the animal’s death, making it difficult to identify the species involved. However, large accumulations of parasites in organ smears are indicative of B. bovis.

B. bigemina parasites are readily detected in the general circulation.

For histopathology, submit samples of brain, spleen, liver and lung.

Species differentiation is important as it influences the choice of preventative treatment and vaccination programs. Anaplasmosis (gall sickness) may present with similar signs and should be excluded. Positive identification of Anaplasma parasites may be difficult in advanced cases. It is common practice to treat such cases with drugs effective against both diseases. Other differential diagnoses include leptospirosis, chronic copper poisoning, and poisoning by Brassica species and Allium species. Cerebral babesiosis can also be confused with other conditions, e.g. rabies, heartwater, plant poisonings and other conditions.

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Disease control

Eradication of tick vectors is rarely practical or cost effective. Allowing natural endemic stability to develop by practising no tick control is not realistic either, especially where R. appendiculatus and Amblyomma are well established. Ideally one should integrate the strategic use of acaricides, the use of vaccines in endemically unstable conditions and the use of tick resistant cattle breeds.

Vaccination

Onderstepoort produces frozen live vaccines against B. bovis and B. bigemina. The strains used in the vaccines are less virulent than natural infection, but they are not entirely safe. Ideally animals should be vaccinated between 2 and 8 months of age, when innate resistance will minimize the risk of reactions. Older animals should be observed daily for 3 weeks after vaccination. Vaccinating pregnant cows is not advised, as abortions may occur.

Vaccines provide protective immunity starting four to six weeks after vaccination. In the case of B. bovis, immunity lasts several years. In the absence of natural challenge, immunity to B. bigemina may break down. However, where the disease occurs naturally that is rarely a problem.

Treatment

The drugs most commonly used, and effective against both Babesia species, are Diminazene e.g. Berenil and Imidocarb, e.g., Forray 65. It is important to follow manufacturer’s instructions and dose rates precisely as both drugs are toxic in overdose, and misuse may result in resistant parasites developing.

Severely affected animals may require supportive treatment, including intravenous fluid, blood transfusions, haematinics, vitamins etc. In acute B. bovis infections antioxidants such as vitamin E and high doses of corticosteroids may help.

Chemoprophylaxis

Imidocarb and diminazene may be used prophylactically for short term control or prevention of Babesia. In an outbreak it may be useful, although expensive, to treat all affected and exposed cattle. It may also be used to protect susceptible cattle when transported through or temporarily residing in an endemic area. This may be combined with intensive dipping in an outbreak, followed by vaccination. Keep in mind that vaccination will not be effective if done too soon after prophylactic treatment. One needs to wait 8 weeks before vaccinating for B. bovis and 16 weeks for B. bigemina in the case of imidocarb and four and eight weeks respectively in the case of diminazene.

Although control procedures during an outbreak will depend on numbers and ease of management, one or more of the following actions may be undertaken to limit losses:

  • Sick animals should be treated and separated from the rest of the herd.
  • The diagnosis should be confirmed at a reputable laboratory.
  • Unaffected animals should be treated for ticks to prevent exposure.
  • Consider immediate vaccination of all unaffected cattle.
  • Consider the use of prophylactic treatment.