Postnatal neosporosis in dairy cattle in northeast Thailand.

A total of 83 dairy cows in Loei Province (Muang) and Nong Bua Lamphu (NBL) Province, northeast Thailand were sampled three times within 6 months in 1998 and their sera were examined for antibodies to Neospora caninum at a dilution of 1:100 in the indirect fluorescent antibody test (IFAT). In Muang the seroprevalence of N. caninum was 37.5% (June), 60% (August), and 62.5% (November). In NBL the prevalence was 50% (August) and 70% (November). In both areas abortions were observed between 1 and 3 months after the introduction of these cattle from another area. Nine of 14 and seven of 17 calves were descendants of seropositive dams, of which only two calves from Muang and two calves from NBL were positive for N. caninum antibodies. These findings suggest postnatal N. caninum transmission.

Influence of Trypanosoma evansi infection on milk yield of dairy cattle in northeast Thailand.

Effect of subclinical Trypanosoma evansi infection on the milk yield of newly introduced Holstein Friesian dairy cattle were investigated. Five hundred pregnant heifers were introduced in Loei Province, northeast Thailand and a total of 168 blood samples were collected at 20 farms during 6 visits over 2 years. Trypanosomes were found in cattle in June and November 1996, after which the parasite was rarely seen. On the other hand, the infection prevalences by antigen-detection ELISA (Ag-ELISA) were around 40% from the first sampling through October 1997; then, antigenemic cattle decreased to 20% by June 1998. Milk yields of the cattle with detectable parasitaemia in June and November 1996 were significantly lower than those of the non-infected cattle by Student's t-test. Similarly, the milk yields of Ag-ELISA positive cattle were lower than those of negative cattle at every sampling and significant differences were observed during the first year and in February, 1998 (tested by 2-way ANOVA; T. evansi status and herd as factors). This study suggested that subclinical trypanosomosis caused decrease in milk yield of newly introduced dairy.

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.

Haemoparasite infections in newly introduced dairy cattle in Loei Province, Thailand: Trypanosoma evansi antigen levels by ELISA referring to abortion.

An antigen-detection enzyme-linked immunosorbent assay (Ag-ELISA) based on affinity-purified polyclonal antibody was utilised as an immunodiagnosis for Trypanosoma evansi infections in cattle. Five hundred pregnant heifers were introduced in Loei province, Thailand and a total of 271 samples were collected at 37 farms during four visits over a year commencing a month after the introduction. Each time the haematocrit centrifuge technique (HCT) was carried out as a field diagnosis for T. evansi, and sera were examined for trypanosomal antigen levels by Ag-ELISA. At the first sampling over 80% of the cattle were positive for trypanosome antigens by Ag-ELISA although the titres were low. Soon after, aborted cases at the late stage of pregnancy were reported and at the second sampling in the rainy season, 25.5% of the cattle sampled were found to harbour T. evansi by HCT. This time the infection rate by Ag-ELISA was 52.9% with high antigen levels. Between the first and second sampling nine cattle out of 51 aborted, which was suspected to be due to T. evansi. As soon as treatment with a trypanocidal drug was started, abortion cases decreased. However, the infection rate remained high during the rainy season when Tabanus flies were active. As the climate became cool and dry, the antigen levels in the area lowered and the positive rate by Ag-ELISA dropped to 32.3%.

Trypanosoma evansi infection in buffaloes in North-East Thailand. II. Abortions.

By exclusion of other possible aetiological agents, strong circumstantial evidence is presented of Trypanosoma evansi infection being the cause of late gestation abortion and stillbirth in buffaloes.