Seroprevalence of antibodies against Coccidioides immitis in healthy horses.

This research studied the presence of antibodies against the fungus Coccidioides immitis in healthy horses based in an area where coccidioidomycosis is prevalent. The study found low levels of such antibodies in about 4% of the healthy horses tested.

Research Objective and Method

• The goal of this research was to investigate the seroprevalence, or the occurrence of a specific antibody in a population, against the fungus Coccidioides immitis in healthy horses. This fungus causes a disease called coccidioidomycosis, which is endemic in certain areas of Arizona.
• A group of 197 healthy horses living in the endemic area, and which had no previous diagnosis of coccidioidomycosis, were studied over a six-month period. These horses were randomly picked from those assessed at the Arizona Equine Medical and Surgical Center.
• The researchers collected serum samples from these horses and tested for the presence of IgM and IgG antibodies against C. immitis using an immunodiffusion assay. Any samples testing positive for IgG antibodies were further assessed quantitatively.
• If a horse tested positive for the antibodies (seropositive), the researchers tried to re-test the horse within six months to confirm the results.

Findings and Conclusion

• The test detected antibodies against C. immitis in 8 of the 197 horses, indicating a seroprevalence of approximately 4.06%. Most of these seropositive horses were positive for IgG antibodies and negative for IgM antibodies, except one horse which tested positive for both types of antibodies.
• The quantity of IgG antibodies was low, with none of the seropositive horses having a titer (the concentration of antibodies in the blood) greater than 8.
• Follow-up data collected from 5 of the seropositive horses revealed either a seronegative result (negative for the presence of antibodies) or an unchanged or reduced titer. This implies that the presence of antibodies against C. immitis in these horses might be temporary or the body’s response to the fungus is decreasing over the time.
• The duration of residence in the area was found to be significantly shorter for the seropositive horses as compared to seronegative ones, suggesting that exposure to the fungus might have been recent.
• Based on the results of the study, the researchers concluded that antibodies against C. immitis can very occasionally be found in healthy horses living in areas where coccidioidomycosis is commonplace. If a horse tests positive for these antibodies, they recommend it should be re-evaluated after at least three weeks to track changes in the antibody titer.