Quantitative analysis of Babesia ovis infection in sheep and ticks.

A quantitative PCR, based on the gene encoding Babesia ovis Surface Protein D (BoSPD) was developed and applied to investigate the presence of Babesia ovis (B. ovis) in its principal vector, the tick Rhipicephalus bursa (R. bursa), and in the ovine host. Quantification of B. ovis in experimentally-infected lambs showed a sharp increase in parasitemia 10-11 days in blood-inoculated and adult tick-infested lambs, and 24 days in a larvae-infested lamb. A gradual decrease of parasitemia was observed in the following months, with parasites detectable 6-12 months post-infection. Examination of the parasite load in adult R. bursa during the post-molting period using the quantitative PCR assay revealed a low parasite load during days 2-7 post-molting, followed by a sharp increase, until day 11, which corresponded to the completion of the pre-feeding period. The assay was then used to detect B. ovis in naturally-infected sheep and ticks. Examination of samples from 8 sheep and 2 goats from infected flocks detected B. ovis in both goats and in 7 out of the 8 sheep. Additionally, B. ovis was detected in 9 tick pools (5 ticks in each pool) and two individual ticks removed from sheep in infected flocks.