Isolation of Babesia divergens from carrier cattle blood using in vitro culture.

Babesia divergens, the main causative agent of bovine babesiosis in Western Europe, was isolated from naturally infected cattle. Ninety-six blood samples were examined by means of an in vitro culture technique in sheep erythrocytes: 19 of them were collected from animals in the acute phase of the disease with visible parasitemia on blood smears, while the 77 remaining animals showed no microscopically detectable parasites. B. divergens was cultured from the 19 first blood samples as well as from 31 samples collected from asymptomatic animals. The time period before parasites could be detected in the culture varied in the latter samples from 6 to 20 days. The effects of sampling condition (anticoagulant used) and storage length were tested. A good correlation was obtained between immunofluorescent antibody test and culture, with identical results (positive or negative) for 89.6% of the samples collected from asymptomatic animals. The sensitivity of the in vitro culture method was determined and was about 10 parasites/mL of whole blood from three independent experiments performed with three different isolates, confirming its suitability to detect and culture diverse B. divergens isolates from carrier cattle. The parasites could indeed be isolated 9 months after the acute babesiosis phase in the blood of naturally infected animals. The 50 isolates collected in this study were successfully subcultured, cryopreserved and resuscitated using the same culture medium. The in vitro isolation of B. divergens from asymptomatic carrier cattle was achieved and will allow the analysis of parasite diversity within cattle herds.