RESUMO
Horses from six stud farms representing the most frequent types of horse breeding in Brazil were tested for Babesia antibodies by the IFA test. The farms are located at the tropic of Capricorn at an altitude of 472-715 m where temperatures below 0 degrees C may occur. Horses of conventional stud farms were infested with Dermacentor nitens, Amblyomma cajennense, and Boophilus microplus. Infestation with Bo. microplus was associated with direct or indirect contact of horses with cattle, and was not detected at professional stud farms. At one large professional stud farm, only D. nitens was observed. Prevalence of Babesia equi correlated positively (p<0.001) with contact of pastured horses to cattle (67.1% versus 17.5%). The IFA test was validated using sera from 92 non-infected horses and from 18 ponies infected experimentally with the USDA strains of B. equi or B. caballi or with the Brazilian isolates from the study area. Differences in test results obtained using antigens from USDA strains or Brazilian isolates were not significant. The specificity was 100% except for the IFA test using Brazilian antigen of B. caballi (98%). The sensitivity was 100% except for the IFA test using the USDA antigen of B. caballi. Accuracy of the tests ranged from 98 to 100%, and predictive values from 99 to 100%. Only 59% (132/224) of sera, positive by the IFA test for B. equi, tested positive by CF test, and 45% (232/515) of sera, positive by the IFA test for B. caballi, also tested positive by CF test. In all, 740 field sera from 140 horses, including 63 mares and their foals, were tested. Prevalence and incidences of B. caballi infections were significantly higher than those of B. equi infections: 49.2% (31/63) of the mares were infected with B. equi, but 79.4% (50/63) with B. caballi; 36% (18/50) of the foals became infected with B. equi within 12 months, but 100% (50/50) with B. caballi within 10 months. Maternal antibodies against B. equi and B. caballi in foals were 44 (22/50) and 68% (34/50), respectively. Titers persisted for 1-5 months for B. equi and 1-4 months for B. caballi.
