Synonyms: Piroplasma argentinum, Francaiella argentina.
Geographic Distribution: South America, Central America, Australia.
Morphology: The trophozoites resemble those of B. bovis. They are piriform, about 2.0 by 1.5 u, and usually lie in the center of the host erythrocyte.
Life Cycle: Similar to that of B. bovis. The vector in South America is Boophilus microplus and that in Australia is B. australis. Transmission takes place thru the egg.
Pathogenesis: In Australia, B. argentina is more pathogenic than B. bigemina (Pierce, 1956). Daly and Hall (1955) found that the mortality in Australian cattle inoculated with B. bigemina was 30% and that of cattle inoculated with B. argentina was 70 to 80%. The clinical signs, lesions, etc. are similar in both diseases.
Immunity: Premunition following recovery from B. argentina infections lasts less than 2 years, and the minimum time at which cattle regain susceptibility is 5 to 6 months (Pierce, 1956). Cattle infected with B. bigemina are resistant to infection with B. argentina (Legg, 1935; Seddon, 1952), but those infected with B. argentina are susceptible to infection with B. bigemina (Seddon, 1952).
Diagnosis: Same as for B. bovis. The trophozoites can be found more easily in smears from the heart or kidney than in the peripheral blood.
Treatment: Same as for B. bovis.