Serologic test for antibody to Sarcocystis in cattle.

Soluble antigen was prepared from Sarcocystis zoites obtained from heart muscle of a bovine inoculated with sporocysts from canine feces and killed 120 days after infection. The antigen was used in an indirect hemagglutination (IHA) test and an agar gel diffusion test to detect antibody to Sarcocystis in experimentally infected cattle. IHA serum titers began to rise 30 to 45 days after infection and reached levels up to 1:39,000 90 days after infection. Sera collected under field conditions from 21 dairy cows had IHA titers ranging from 1:54 to 1:486. Since all cows appeared in good health, titers of 1:486 or less can probably be considered nonsignificant with regard to diagnosis of clinical disease. No positive Sarcocystis IHA titers were obtained with human sera previously found to be IHA positive for toxoplasma, indicating a lack of cross reactivity between antigens. Precipitins in the agar gel diffusion test appeared 30 days postinoculation and became very pronounced at 65 to 90 days.