Serological Diagnosis of Babesia bigemina Infection in Cattle by the Indirect Fluorescent Antibody Test

An indirect fluorescent antibody (IFA) test is described for the detection of Babesia bigemina antibodies in bovine serum. A method is described for the preparation of antigen smears which virtually eliminates confusing background fluorescence. A microstaining technique is used affording considerable economy of test reagents. The test is considered to be highly specific and accurate (100% in 100 known control sera) and sufficiently sensitive to detect reactors infected 2 years previously. Susceptible and immune clinical responses are obtained when groups of negative and positive reactors to the IFA test are challenged with B. bigemina infected blood, demonstrating, in addition to test reliability, a correlationship between protective antibodies and those detectable by immunofluorescence. IFA tests of sera collected regularly over 6 months show initial responses following rapidly the pre-patent period, reaching peaks at 21 days after infection, with maximum titres up to 1:1,280 waning gradually thereafter, but still above minimum levels at the end of the period. Some evidence is produced indicating a continued downward trend with minimum positive IFA responses still detectable 18 to 24 months after a single experimental infection.