Bovine Babesiosis (Redwater, Tick Fever)
Bovine Babesiosis (BB) is a tick-borne disease of cattle.
The principal strains are babesia bovis and babesia bigemina, with Rhipicephalus ticks being the major vector.
Babesia divergens is also found, with the major vector being Ixodes ricinus.
BB is found in areas where its arthropod vector is distributed, especially tropical and subtropical climates. Babesia bovis and B. bigemina are more widely distributed and of major importance in Africa, Asia, Australia, and Central and South America. Babesia divergens is economically important in some parts of Europe and possibly northern Africa.
Transmission of B bovis takes place when engorging adult female ticks pick up the infection. They pass it on to their progeny via their eggs. Larvae (or seed ticks) then pass it on in turn when feeding on another animal. B bigemina is also passed from one generation of ticks to the next. Engorging adult ticks pick up the infection and nymphal and adult stages (not larval stages) of the next generation pass it on to other cattle.
Morbidity and mortality vary greatly and are influenced by prevailing treatments employed in an area, previous exposure to a species/strain of parasite, and vaccination status. In endemic areas, cattle become infected at a young age and develop a long-term immunity. However, outbreaks can occur in these endemic areas if exposure to ticks by young animals is interrupted or immuno-naïve cattle are introduced. The introduction of Babesia infected ticks into previously tick-free areas may also lead to outbreaks of disease.
BB is predominantly observed in adult cattle. Infected animals develop a life-long immunity against re-infection with the same species and some cross-protection is evident in B. bigemina-immune animals against subsequent B. bovis infections.B. bovis
Conditions are often more severe than other strains.
- High fever
- Parasitaemia (percentage of infected erythrocytes) - maximum parasitaemia is often less than one per cent.
- Neurologic signs such as incoordination, teeth grinding and mania. Some cattle may be found on the ground with the involuntary movements of the legs. When the nervous symptoms of cerebral babesiosis develop, the outcome is almost always fatal.
- Dark coloured urine
- Animals likely to separate from herd, be weak, depressed and reluctant to move
- Haemoglobinuria and anaemia Dark coloured urine
- Central nervous system (CNS) signs are uncommon
- In b. bigemina parasitaemia often exceeds 10 per cent and may be as high as 30 per cent.
Clinical symptoms for Babesia divergens are similar to B. bigemina infections.
The survivors may be weak and in reduced condition, although they usually recover fully. Subacute infections, with less apparent clinical signs, are also seen.
Mild cases may recover without treatment.
Sick animals can be treated with an antiparasitic drug. Treatment is most likely to be successful if the disease is diagnosed early; it may fail if the animal has been weakened by anemia.
Imidocarb has been reported to protect animals from disease but immunity can develop. There are also concerns with regard to residues in milk and meat.
In some cases blood transfusions and other supportive therapy should be considered.
Effective control of tick fevers has been achieved by a combination of measures directed at both the disease and the tick vector. Tick control by acaracide dipping is widely used in endemic areas.
Dipping may be done as frequently as every 4-6 weeks in heavily infested areas. The occurrence of resistance of ticks, chemical residues in cattle and environmental concerns over the continued use of insecticides has led to use of integrated strategies for tick control.
Babesiosis vaccines are readily available and are highly effective. Anti-tick vaccines are also available in some countries and can be used as part of an integrated program for the control of ticks.
Babesiosis can be eradicated by eliminating the host tick(s). In the US, this was accomplished by treating all cattle every two to three weeks with acaricides. In countries where eradication is not feasible, tick control can reduce the incidence of disease.
Babesiosis resembles other conditions that cause fever, and hemolytic anemia. The differential diagnosis includes anaplasmosis, trypanosomiasis, theileriosis, bacillary hemoglobinuria, leptospirosis, eperythrozoonosis, rapeseed poisoning and chronic copper poisoning. Rabies and other encephalitides may also be considerations in cattle with central nervous system signs.
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