90. Myth or Real? The seroprevalence (the level of a pathogen in a population determined by using blood serum) for the causative agents of Equine Protozoal Myeloencephalitis (EPM) in horses is the same regardless of region of the country or breed of horse.

Answer: Myth

EPM is one of the most common neurological diseases affecting horses in North America. A recently published article looked at the seroprevalence of both Sarcocystis neurona and Neospora hughesi (protozoan agents responsible for EPM in horses) utilizing the blood samples drawn from 5,250 horses in 18 states across the US. Information was also gathered at the time of the blood draw to look at potential risk factors such as geographic region, breed, age, sex and primary use. The results showed the seroprevalence of S. neurona to be 78% and N. hughesi 34% in the 5,250 horses sampled. 31% of horses were positive for both while only 18% were negative for both. The results for geographic region showed horses most at risk for S. neurona to reside in the south region and the lowest risk were those horses in the west region. Horses residing in the south were also most at risk for N. hughesi as well. In this study, warmbloods and thoroughbreds had greater odds of being positive when compared to the quarter horse breed. While primary use didn’t seem to be a factor, the authors note that different management practices associated with different breeds in different regions could increase the risk of a horse’s exposure. Because the definitive host for S. neurona is the opossum, regional differences in seroprevalence could be due to regional differences in population numbers of infected opossums. One interesting note is that in looking at N. hughesi, both breed (warmblood) and sex (males>females) both were considered to be risk factors for a positive blood test. Age, >5 years, was also determined to be a risk factor but this is not surprising and is it thought that these higher titers could be due to persistent infection. The authors concluded, “equids in regions previously considered to be at low risk of infection with S. neurona and, perhaps more
importantly, with N. hughesi have potentially higher rates of infection than previously thought.” It was recommended that veterinarians in all regions of the country consider testing all equids with suspected EPM for both protozoan agents.

Article: James, KE, et. al. Seroprevalence of anti-Sarcocystis neurona and anti-Neospora hughesi antibodies among healthy equids in the United States. JAVMA, vol. 250, no. 11, June 1, 2017. pp. 1291-1300.

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