Serosurvey of horses with evidence of equine monocytic ehrlichiosis.

The research article is about a study on the prevalence of a particular disease (equine monocytic ehrlichiosis or EME) in horses. The disease is identified through the presence of specific antibodies (IgG and IgM) in horses at two racetracks in Ohio, with a focus on disease frequency, illness statistics, and correlation with the location of stabling.

Research Context

• The study on equine monocytic ehrlichiosis (EME) was carried out in the year 1986, specifically focusing on horses in two Ohio racetracks, River Downs (RD) and Beulah Park (BP).
• This disease – EME is caused by a pathogenic microorganism, Ehrlichia risticii, with the presence of specific antibodies (IgG and IgM) indicating infection.

Research Findings: Seroprevalence

• From a total population of 840 horses at RD and 574 at BP, 13% and 20%, respectively, had IgG antibodies against Ehrlichia risticii.
• These antibodies were detected using an indirect fluorescent antibody test, with the measured antibody titers ranging from 1:20 to 1:10,240. The most common titer observed at both tracks was 1:80.
• More horses were found to be sick at RD, which operates during the summer months compared to BP, which is a winter track.

Research Findings: Correlation with Illness

• Among ill horses, 41% at RD and 58% at BP showed evidence of previous exposure to the causative organism (seropositive).
• Of the horses that tested positive for IgG antibodies at RD, 95% had been stabled only at RD during the month prior to testing. This suggests a possible localized source of infection.

Research Findings: IgM Antibodies and Recent Infections

• IgM antibodies, which appear early in an infection, were also searched for. At RD, 57 out of 137 seropositive horses were also positive for IgM antibodies, implying recent infections. At BP, 20 out of 120 seropositive horses were positive for IgM.
• It was concluded that a greater number of horses were recently infected at RD than at BP.

Conclusions

• Based on the above findings, it was inferred that about half of the seropositive horses at RD may have acquired the infection at RD itself.
• An important finding of this survey is the high number of subclinical infections found among seropositive horses – 78% at BP and 91% at RD. These horses carried antibodies for EME but did not exhibit visible symptoms.
• At antibody titers of 1:40 or lesser, there were no differences in seropositive rates among healthy and ill horses.