Molecular investigation of Babesia caballi in horses from the state of Rio de Janeiro, Brazil: Epidemiological aspects associated with the infection.

The epidemiological aspects of Babesia caballi infection were evaluated in 516 horse samples from Rio de Janeiro, Brazil. The presence and infestation level of ticks on horses, breed conditions, and animal management were evaluated on each farm through an epidemiological questionnaire. The gene that codes for rhoptry-associated protein-1 (RAP-1) of B. caballi was amplified by nested PCR (nPCR). Among the horses sampled, 17.2% (n = 89/516) presented B. caballi DNA. The characterized samples showed 99-100% similarity with other isolates of B. caballi based on the RAP-1 gene, available in GenBank. In the final logistic regression model, the variables associated with B. caballi infection in horses were as follows: age below two years (OR = 3.33; IC = 1.7-6.5), farms located in low altitudes (OR = 3.52; IC = 1.7-7.3) and Dermacentor nitens infestation (OR = 1.91; IC = 1.1-3.4). Furthermore, a high level of D. nitens infestation in horses was also a factor associated with positivity for B. caballi (OR = 2.11; IC = 1.25-3.54). In summary, young horses bred in low altitude regions characterized with high temperatures, and infested by D. nitens, mainly with a higher level of infestation, are more likely to be infected by B. caballi. This epidemiological study provides statical evidence that the D. nitens tick play a role as the biological vector of B. caballi in the studied region.