Seroepidemiologic studies on Babesia equi and Babesia caballi infections in Brazil

Horses from six stud farms representing the most frequent types of horse br eeding in Brazil were tested for Babesia antibodies by the IFA test. The fa rms are located at the tropic of Capricorn at an altitude of 472-715 m wher e temperatures below 0 degrees C may occur. Horses of conventional stud far ms were infested with Dermacentor nitens, Amblyomma cajennense, and Boophil us microplus. Infestation with Bo. microplus was associated with direct or indirect contact of horses with cattle, and was not detected at professiona l stud farms. At one large professional stud farm, only D. nitens was obser ved. Prevalence of Babesia equi correlated positively (p < 0.001) with cont act of pastured horses to cattle (67.1% versus 17.5%). The IFA test was val idated using sera from 92 non-infected horses and from 18 ponies infected e xperimentally with the USDA strains of B. equi or B. caballi or with the Br azilian 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 10 0%, and predictive values from 99 to 100%. Only 59% (132/224) of sera, posi tive 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 infectio ns 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. caball i; 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 agai nst B. equi and B. caballi in foals were 44 (22/50) and 68% (34/50), respec tively. Titers persisted for 1-5 months for B. equi and 1-4 months for B. c aballi. (C) 1999 Elsevier Science B.V. All rights reserved.