Tick fever, Cattle fever, Texas fever, Piroplasmosis, Redwater
Bovine babesiosis is a tick-borne, parasitic infection that causes significant morbidity and mortality in cattle. It is the most important arthropod-borne disease of cattle worldwide.

Etiology

Babesiosis results from infection by protozoa in the genus Babesia (family Babesiidae, order Piroplasmida). The three species found most often in cattle are Babesia bovis, B. bigemina and B. divergens. Additional species that can infect cattle include B. major, B. ovata, B. occultans and B. jakimovi. Organisms that are very closely related to B. divergens, but do not seem to affect cattle, have recently been discovered in wildlife and humans.

Transmission

Babesia species are transmitted by ticks, which become infected when they ingest parasites in the blood of infected cattle. The major vectors for B. bigemia are Rhipicephalus microplus (formerly Boophilus microplus) and R. annulatus (formerly Boophilus annulatus). R. decoloratus, R. geigyi, and R. evertsi can also transmit this species. The major vectors for B. bovis are R. microplus and R. annulatus, but R. geigyi can also be a vector. B. divergens is transmitted mainly by Ixodes ricinus. B jakimovi may also be transmitted by an Ixodes species. Haemaphysalis punctata transmits B. major, Haemaphysalis longicornis transmits B. ovata, and Hyalomma marginatum transmits B. occultans.

Clinical Signs

The clinical signs vary with the age of the animal and the species and strain of the parasite. Most cases of babesiosis are seen in adults; animals younger than 9 months usually remain asymptomatic. Strains vary considerably in pathogenicity; however, B. bovis is usually more virulent than B. bigemina or B. divergens. Typically, animals infected with B. bigemina develop anorexia and a high fever; fever may be present before other clinical signs appear. The characteristic signs are caused by hemolysis and anemia. Animals become inappetent, may separate from the herd, and are weak, depressed and reluctant to move. The mucous membranes become pale, and respiration and heart rate increase. Anemia often develops rapidly, and is frequently accompanied by hemoglobinuria and hemoglobinemia. Jaundice occurs mainly in subacute cases.

Control

Babesiosis can be eradicated by eliminating the host tick(s), by treating all cattle every 2 to 3 weeks with acaricides. In countries where eradication is not feasible, tick control can reduce the incidence of disease. Live, attenuated strains of B. bovis, B. bigemina or B. divergens are used to vaccinate cattle in some countries. In endemic areas, sick animals should be treated as soon as possible with an antiparasitic drug. Chemoprophylaxis with one drug (imidocarb) can protect animals from clinical disease while allowing the development of immunity.