Risk of transplacental transmission of Sarcocystis neurona and Neospora hughesi in California horses.

This research paper studied the risk of transmission from mother to foetus of two parasitic infections, Sarcocystis neurona and Neospora hughesi, in horses in California. The study found no evidence of transmission, but did note an increase in infection rates in older mares, with those having previously aborted at higher risk.

Study Objective and Methodology

• The research aimed to evaluate the risk of transplacental transmission (from mother to foetus during pregnancy) of two parasites, Sarcocystis neurona and Neospora hughesi, in foals from four Californian farms over three foaling seasons.
• This involved testing the serum of new-born foals before they began to suckle, and the serum and colostrum (a type of milk produced after giving birth which contains antibodies) of mares around the time of giving birth. Testing was done using indirect fluorescent antibody tests for each of the parasites.

Results

• In the 366 foals tested before suckling, no significant quantities of antibodies against the parasites were found, implying no infection.
• No evidence of either parasite was found in any aborted foetuses or placentas investigated.
• The risk of mares testing positive for S. neurona and N. hughesi was found to increase with age, suggesting an increased exposure risk over time.
• Mares aged nine years or less that were from Kentucky were more likely to test positive for both parasites, by factors of 3.8 and 1.4 respectively, than equivalent mares from California.
• The significance of place of birth as a predictor for parasitic infection decreased as mares aged.
• Mares testing positive for either parasite were more likely (2.2 times for S. neurona, 1.7 times for N. hughesi) to have had a previous abortion, when factoring in age and place of birth. This could indicate that these infections increase the risk of abortion.
• The annual mortality rate for mares was revealed to be 4%, while the annual rate of incidence of equine protozoal myeloencephalitis (a disease caused by various protozoan parasites that can lead to inflammation of the brain) was 0.2%.

Conclusion

• The study concluded that there was no detectable risk of transplacental transmission of S. neurona and N. hughesi in horses, despite an increase in the prevalence of antibodies against both parasites in mares as they aged.