Evaluation of travel and use as a risk factor for seropositivity to Ehrlichia risticii in horses of New York state.

This study investigates how the frequency and location of travel by horses affects their exposure to Ehrlichia risticii, a horse health risk factor, and how these associations are modified by the horses’ place of residence. Researchers visited 511 horse operations, totaling 2,587 horses in New York state, testing them for serum antibodies against E risticii. The researchers found that horses’ place of residence and certain types of travel to specific risk regions were associated with higher risk of exposure to E risticii.

Methodology

• Researchers carried out a cross-sectional study involving a total of 2,587 horses from 511 equine operations in New York state. This was a sizeable selection from a target population of 39,000 operations.
• Each horse was tested for the presence of serum antibodies against Ehrlichia risticii through indirect fluorescent antibody testing. This disease is known to affect horses’ health and the existence of these antibodies indicates exposure.
• Additional data on each horse’s travel history, their farm’s management practices, and local ecology were gathered through personal interviews and using resource maps.
• The study was carried out on two cohorts: all horses involved in the study and another cohort of horses that were born on the property or had lived at the farm for at least four years.
• Three county-based risk regions were established using cluster analysis.

Findings

• The researchers established mean seroprevalence for each of the three risk regions (RR), identifying regions of low, moderate, and high risk for exposure to E risticii.
• For the first cohort, the prevalence was 2.4% for low risk, 8.5% for moderate risk, and 18.5% for high risk. For the second cohort of horses, the prevalence was slightly different, with 2.5% for low, 8% for moderate and 18.4% for high risk regions.
• Among the two cohorts, pleasure riding and breeding trips were identified as activities associated with increased exposure to E risticii. The risk varied depending on the horse’s residence region.
• Horses from the first cohort that traveled for trail riding in either low or high risk regions showed increased exposure. For the second cohort, breeding trips were associated with exposure, with significant effect modification present for the horse’s residence.

Conclusions

• The research concluded that only specific types of travel to certain risk regions correlated with higher risk of exposure to E risticii.
• In many instances, travel was not linked to increased exposure. In some cases, travel was even associated with reduced risk of exposure.