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The accuracies of two ELISAs, one using antigen from merozoites of S. cruzi grown in vitro and the other using antigen from cystozoites of S. cruzi, for detecting infection of cattle with Sarcocystis, were evaluated by testing the sera of 303 cattle from 36 Western Australian herds. The results were compared with those obtained by digestion of oesophageal samples collected from the same animals. A similar proportion of infected animals were detected by the three methods. The sensitivity of the assays for detecting infected cattle was comparable (98 and 95% for the assay using antigen from merozoites and cystozoites, respectively), however the specificity (97%) of the assay which used antigen derived from merozoites was significantly higher (P < 0.001) than that (84%) which used antigen from cystozoites. When herds which had at least five animals sampled were considered, the same infected and non-infected herds were detected by the ELISA employing antigen from merozoites and the digestion methods (sensitivity and specificity of 100%). The sensitivity and specificity of the assay using cystozoite antigen were 100 and 67%, respectively. The kappa values for agreement beyond chance between the two ELISAs were calculated as 78% for the animal-based data and 72.5% for the herd-based data. We conclude that because of the high sensitivity and specificity of the ELISA using antigen derived from merozoites, this assay would be a useful and reliable tool for general sero-epidemiological studies into infection with Sarcocystis.

Oesophagus samples from 714 cattle from Western Australia were examined by artificial digestion to detect the presence of Sarcocystis spp. The overall prevalence of infection was 52%. The prevalence of infection increased with age and was highest in the entire males (92%). The prevalence was lower in cattle which originated from arid and semiarid regions (9 and 31% respectively) than those from tropical (87%) and temperate (60%) regions. Possible reasons for these differences are discussed and it is concluded that environmental and management factors as well as host age and sex influence the prevalence of infection with Sarcocystis spp. in cattle.