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%.