Controlled interventions using pyrantel tartrate to prevent Sarcocystis neurona infection in horses

This dissertation describes two studies investigating the efficacy of pyrantel tartrate in preventing infection with the protozoan parasite Sarcocystis neurona in horses. Sarcocystis neurona is the primary etiologic agent of equine protozoal myeloencephalitis (EPM), a neurological disease of horses and ponies of the Americas. A third study described here details the culture of S. neurona from the blood of an immunocompetent horse.; In the first study, 24 horses were challenged with sporocysts of S. neurona. Twelve of the horses received daily doses of pyrantel tartrate, 12 received a look-alike placebo pellet. Production of serum antibodies against S. neurona was the main outcome of interest, as this is evidence the parasite was not killed in the gastrointestinal tract by the drug and that the parasite had penetrated host defenses. Production of antibodies in cerebrospinal fluid (CSF) was a second outcome of interest. At the end of the study there was no significant difference between treatment groups with regard to the proportion of horses testing positive or the days to seroconversion.; In the second study, a field intervention trial was conducted on three Michigan horse farms to determine whether daily administration of pyrantel tartrate could prevent infection with S. neurona in horses when the drug was used in an on-farm setting, according to label instructions for Strongid C® 2x. The outcome of interest was the production of serum antibodies to S. neurona. Horses were screened negative by immunoblot for serum antibodies to S. neurona and allocated into two treatment groups: pyrantel tartrate and placebo. Ten horses were monitored for seroconversion for 6 months. The results of the study were inconclusive, due to the small sample size, and no treatment effect was detected.; In the third study, six yearling colts given daily doses of S. neurona sporocysts, were selected for attempted culture of S. neurona from whole blood. Two 10 ml tubes of blood in EDTA were collected from each horse. Plasma was removed from the tubes and processed to remove fibrinogen and cultured on equine dermal cells. Thirty-eight days later the culture from one horse was positive. To our knowledge, this is the first report of parasitemia in an immunocompetent infected with S. neurona sporocysts.