Parasitemia in an immunocompetent horse experimentally challenged with Sarcocystis neurona sporocysts.

This research article focuses on the detection of parasitemia in a healthy horse that was deliberately exposed to Sarcocystis neurona, a parasite associated with a severe neurological disorder in horses. The experiment found that the parasite was able to be detected in the blood of the horse, marking the first such discovery in a healthy horse.

Background of the Study

• The researchers embarked on this study to determine if viable Sarcocystis neurona (S. neurona) could be isolated from the blood of healthy horses. Health in this context refers to immunocompetent: horses with a functioning immune system. Previously, parasitemia (parasites in blood) had not been demonstrated in immunocompetent horses, but had been documented in one immunocompromised foal (a foal with a weak immune system).
• S. neurona is the parasitic cause of most cases of equine protozoal myeloencephalitis (EPM), a serious neurological disease affecting horses primarily in the Americas.

Methodology of the Study

• The researchers exposed the horses to the S. neurona by orally administering sporocysts (a stage of the parasite life cycle) daily for 112 days at gradually increasing doses.
• On Day 98 of the study, blood was drawn from six yearling colts chosen from the group. The selection involved two colts that had tested positive for anti-S. neurona antibodies, two suspect, and two negative on Day 84.
• The plasma rich in mononuclear cells was then added to equine dermal cell cultures and monitored for parasite growth for 12 weeks.
• To verify the species of any parasites found, the researchers used a method called PCR with RFLP and sequenced the PCR products for comparison with known S. neurona strains.

Results of the Study

• One cell culture from a horse that had tested positive for antibodies against S. neurona indicated parasite growth after 38 days of incubation.
• The five remaining cultures showed no sign of parasite growth throughout the 12 weeks.
• The Sarcocystis isolate recovered from the cell culture was verified to be S. neurona. Its gene sequence revealed it was identical to the SN-37R strain used in the challenge and differed from two other known strains, UCD1 and MIH1.

Significance of the Findings

• This is reportedly the first case of detecting parasitemia with S. neurona in a healthy horse.
• This discovery expands our understanding of how S. neurona can affect horses and may have important implications for diagnosing and managing EPM in the equine population.