Seroprevalence of antibodies to Neospora caninum and associated abortion in dairy cattle from central Thailand.

A total of 904 sera from dairy cattle in 11 provinces of central Thailand were tested for antibodies to Neospora caninum employing the indirect fluorescent antibody test (IFAT). Fifty four (6%) cattle were positive in IFAT, titres of 1:200 (16 cattle), 1:400 (9 cattle), 1:800 (14 cattle), 1:1600 (7 cattle), 1:3200 (6 cattle) and two positives. No significant difference was observed among the provinces. The seropositivity for Toxoplasma gondii by a commercial latex agglutination test was 4% (2 out of 50) in positive sera, 2.9% (2 out of 69) in negative sera for anti-Neospora antibodies and 3.4% (4 out of 119) in total. The results of the IFAT were not associated with the presence of antibodies to T. gondii in bovine sera. Furthermore, the cause of abortions experienced in neighbouring three areas in the northeast, where pregnant heifers were newly introduced into small-scale farms from the central region, was investigated. The positive rates for anti-N. caninum antibody were 12, 28 and 44% at a cut-off titre of 1:200, and cattle were suspected to be infected after the introduction. In the area with the highest rate, seven out of eight aborting cattle were positive for antibodies to N. caninum while other two areas had similar abortion rates in both negative and positive cattle. However, in the latter two areas, positive rates for Trypanosoma evansi antigen along with parasitaemic animals were observed by an antigen-detection ELISA, but not for the former area. Considering the endemic diseases of the areas, Neospora was presumed to be responsible for the abortions in the former area while the examination results pointed out T. evansi as the most probable cause in the latter two areas. This is the first report of Neospora-associated abortion in Southeast Asia.