Serologic response of Babesia equi-infected horses as measured by complement-fixation and indirect fluorescent antibody tests.

The research focuses on examining responses of horse serum samples infected with Babesia equi, a tick-borne disease, using two types of tests: Complement-fixation test (CFT) and Indirect Fluorescent Antibody Test (IFAT). The study finds that both methods successfully diagnose infection; however, the IFAT shows positivity and higher relative serum titer increases earlier than the CFT.

Methodology

• The researchers conducted the CFT and IFAT on serum samples from nine Arab geldings, obtained weekly for 28 days before and 256 days after exposure to Babesia equi of European origin.
• The tests were designed to measure the response of these horses to the disease.

Findings

• The IFAT became positive about 8 days earlier than the CFT, indicating quicker detection of the disease.
• Relative serum titer increases, indicative of the body’s immune response, were higher in the IFAT than in the CFT.
• Both tests continually detected the presence of infection with no significant drop in titer, a measurement of the concentration of antibodies.
• There was an observed brief drop in titer after treatment with imidocarb in the CFT, while the IFAT demonstrated stability.

Long-Term Analysis

• A follow-up test conducted 540 days post-infection showed inconsistencies between the two methods tested. The CFT showed negative results in four of the eight surviving horses, suggesting they were no longer infected. However, the same horses tested positive for infection using IFAT.

Comparison of Antigens

• When the IFAT was used to compare serums from B. equi infections of both European and North American origins, using homologous (same origin) and heterologous (different origin) antigens, the tests showed significantly higher titers when using homologous antigens.

Conclusion

• Overall, the study suggests that the IFAT might be more sensitive and reliable in diagnosing and tracking Babesia equi infection in horses over time. However, further study is warranted to confirm these findings and understand the discrepancies observed between the two methods.