Transmission and clinical evaluation of an equine infectious anemia herd and their offspring over a 13-year period.

This research paper examines the transmission and clinical evaluation of an equine infectious anemia (EIA) herd and their offspring over a 13-year period, confirming certain findings about the disease’s transmission and clinical forms.

Research Context

• The study was initiated in response to intense outbreaks of EIA in New York and New Jersey during and before 1970, particularly in the Great Swamp Area of New Jersey. This area was highly conducive to insect transmission of the disease.
• The investigation was established on a 3,000-acre farm in New Jersey, which housed EIA chronic horses. Approximately 150 horses have been involved in the research over the years.
• Considered as part of the study were horses in an acute, subacute, and chronic state of EIA. Acute horses show signs of debilitation, high body temperature, anemia, and weakness. Subacute horses have less obvious signs but still offer clinical evidence of the disease. Chronic horses show no symptoms.

Herd Study

• The farm in New Jersey initially kept a herd of 97 horses for research purposes. It included different types of horses, including breeding mares, stallions, foals, geldings, and test ponies.
• The researchers intended to limit the herd to chronic, asymptomatic EIA horses, unless the horses experienced conversion to acute or subacute status while on the farm.
• The control methods used involved breed management under clinical field conditions and monitoring of the insect population. Horses were also pastured with local deer and cattle, and negative control horses shared pastures with EIA-positive animals.
• Diagnosis of EIA involved pony inoculations of blood, colostrum, milk, and semen, alongside utilizing the Coggins agar gel immunodiffusion test.

Transmission Study

• The researchers primarily considered insect transmission of EIA, especially through horseflies which can transfer significant amounts of blood.
• 46 foals were produced as part of the research program, resulting from different combinations of seropositive and seronegative parents.
• As the herd grew, it was put under quarantine and became challenging to maintain. All EIA positive horses were euthanized by the end of the year.

Conclusion

• The resulting foals were studied over the years under quarantine, with most of them separated from their mares shortly after birth and reared on artificial milk replacer.
• Nineteen horses resulting from breedings between 1971 to 1974 were relocated to the New England Institute of Comparative Medicine in Massachusetts for ongoing studies.
• The researchers evaluated horses that could test positive for either antigen or antibody on the ELISA test but were negative on the immunodiffusion test.
• It was consistently found that all horses tested negative for EIA antibody when examined via the immunodiffusion and ELISA tests.