An Equine Protozoal Myeloencephalitis Challenge Model Testing a Second Transport After Inoculation With Sarcocystis Neurona Sporocysts

Abstract

Previous challenge studies performed at Ohio State University involved a transport-stress model where the study animals were dosed with Sarcocystis neurona sporocysts on the day of arrival. This study was to test a second transportation of horses after oral inoculation with S. neurona sporocysts. Horses were assigned randomly to groups: group 1, transported 4 days after inoculation (DAI); group 2, at 11 DAI; group 3, at 18 DAI; and group 4, horses were not transported a second time (controls). An overall neurologic score was determined on the basis of a standard numbering system used by veterinarians. All scores are out of 5, which is the most severely affected animal. The mean score for the group 1 horses was 2.42; group 2 horses was 2.5; group 3 horses was 2.75; and group 4 horses was 3.25. Because the group 4 horses did not have a second transport, they were compared with all other groups. Statistically different scores were present between group 4 and groups 1 and 2. There was no difference in the time of seroconversion between groups. There was a difference between the time of onset of first clinical signs between groups 1 and 4. This difference was likely because of the different examination days. Differences in housing and handling were likely the reason for the differences in severity of clinical signs. This model results in consistent, significant clinical signs in all horses at approximately the same time period after inoculation but was most severe in horses that did not experience a second transport.

A Ribeiroia Spp. (Class: Trematoda)–-Specific PCR-Based Diagnostic

“…Toxoplasma gondii oocysts were found in the feces of 13 of 200 cats from Mexico (de Aluja and Aguilar, 1977). For epidemiologic studies, serologic surveys in cats are more useful than the detection of oocysts, because at any given time only 1% of cats shed oocysts in their feces (Dubey, 2004). In the present study, 21% of cats were seropositive for T. gondii, and they likely were shedding oocysts, thereby contaminating the environment.…”

“…Schizonts and merozoites are the only stages known in the horse, and they are found only in the central nervous system (CNS) following an uncharacterized migratory route. Attempts to demonstrate S. neurona in tissues of horses fed sporocysts have been unsuccessful despite the fact that horses developed neurological signs (Fenger et al, 1997;Lindsay et al, 2000;Cutler et al, 2001;Saville et al, 2001;Sofaly et al, 2002). In the present article, we have attempted to follow the migration of S. neurona in tissues of ponies by orally inoculating them with large numbers of sporocysts and examining at shorter postchallenge intervals.…”

“…Sarcocystis neurona has a 2-host life cycle, including a meateating definitive host, the opossums Didelphis virginiana and Didelphis albiventris (Dubey, Lindsay, Kerber et al, 2001;Dubey, Lindsay, Saville et al, 2001). There is a wide range of intermediate hosts, including the raccoon (Dubey, Saville et al, 2001), armadillo (Cheadle, Tanhauser et al, 2001), skunk (Cheadle, Yowell et al, 2001), sea otter (Dubey et al, 2002), and the domestic cat (Dubey and Hamir, 2000;Dubey et al, 2000;Turay et al, 2002). The horse is considered an aberrant intermediate host (Dubey, Lindsay, Saville et al, 2001).…”

Equine Protozoal Myeloencephalitis: An Updated Consensus Statement with a Focus on Parasite Biology, Diagnosis, Treatment, and Prevention

“…Factors such as variations in protozoal inoculum and stress‐induced immune suppression have been implicated in the occurrence of EPM 36, 37, 38. However, efforts to increase stress (ie, by additional transport of infected horses) and treatment with immunosuppressive steroids did not cause a concomitant increase in disease severity 39, 40. Genetic variation has been observed among the strains of S. neurona that have been analyzed,41, 42, 43 and there is some evidence that specific parasite genotypes may be particularly virulent in marine mammals 44.…”

Equine Protozoal Myeloencephalitis

“…As mentioned, factors such as parasite inoculum and stress-induced immune suppression have been implicated in the occurrence of EPM. [45][46][47] However, efforts to increase stress by use of a second transport and treatment with immunosuppressive steroids did not exacerbate disease, 48,49 so it is apparent that the interplay between immune suppression and infection is more complex than currently understood. Modest genetic and antigenic diversity exist among strains of S neurona that have been isolated, [50][51][52] and there is some suggestion that particular parasite genotypes may be more virulent than others.…”