Eperythrozoon ovis. I. Serological diagnosis of infection by the indirect immunoflurescent antibody test.

The indirect immunofluorescent antibody test (IFAT) was evaluated for the detection of Eperythrozoon ovis infection in sheep. The test first became positive, on the average, 10 days following exposure to E. ovis and remained positive for 24 months, the longest period checked. Reciprocal titres in the first three days after becoming positive in the IFAT were between 4 and 80, but rose to 640 within 9 weeks; in general titres were between 4 and 640, exceptionally titres of 1280 were obtained. Negative sera produced no fluorescence at serum dilutions of 1:4. Paired serum samples collected before and after experimental infection demonstrated the specificity of the test. Further support for the specificity and reliability of the IFAT was provided by lack of cross-reactivity between E. ovis antigen and antisera to Anaplasma ovis and Theileria ovis, the two common blood parasites of sheep and goats in Nigeria, and the results of a longitudinal survey in a flock of sheep on the research farm where E. ovis was first detected.