Synonym: Piroplasma caballi.
Hosts: Horse; transmissible to mule and donkey.
Geographic Distribution: Southern Europe thru Asia, USSR, North and South Africa, Central America.
Morphology: This is a large species, resembling B. bigemina. The trophozoites are piriform and 2.5 to 4 u long, or round or oval and 1.5 to 3 u in diameter. The piriform trophozoites are often found in pairs at an acute angle to each other.
Life Cycle: Similar to that of B. bigemina. The vectors in Europe and the USSR are Dermacentor marginatus (syn., D. reticulatus), D. pictus, D. silvarum, Hyalomma anatolicum (syn., H. excavatum), H. marginatum (syn., H. detritum), H. volgense, Rhipicephalus bursa and R. sanguineus. The vector in North Africa is Hyalomma dromedarii. Transmission thru the egg occurs in D. marginatus, D. silvarum, H. marginatum, H. volgense, R. sanguineus and H. dromedarii. Stage-to-stage transmission occurs in D. marginatus, D. pictus, H. anatolicum, H. marginatum, R. bursa and R. sanguineus. B. caballi has also been found in fetuses (Neitz, 1956).
Pathogenesis: The symptomatology of this disease varies markedly. The disease may be either acute or chronic; in either case it may be relatively mild or severe, ending in death. Hemoglobinuria is rare, but fever, anemia and icterus are present. Gastro-enteritis is common. Locomotor signs are usually present, and posterior paralysis may occur. The incubation period is 7 to 19 days. In fatal cases death occurs a week to about a month after the appearance of symptoms.
Immunity: Young animals are less susceptible than old ones. There is no cross-immunity between B. caballi and B. equi.
Diagnosis: Because of the varied symptomatology, diagnosis depends upon identification of the parasites in stained blood smears. They are most numerous in the blood during the first febrile attack.
Treatment: Trypan blue is quite effective against B. caballi, but acaprin and acriflavine are better. Trypan blue is given intravenously, 50 to 75 ml of a 1% aqueous solution being injected. Acaprin is given subcutaneously, 1.2 ml of a 5% solution being injected per 100 kg. Acriflavine is injected intravenously, 20 ml of a 5% solution being given.
Prevention and Control: Same as for B. bigemina.