Ancient, globally distributed lineage of Sarcocystis from sporocysts of the Eastern rat snake (Pantherophis alleghaniensis) and its relation to neurological sequalae in intermediate hosts.

There is an emerging concern that snakes are definitive hosts of certain species of Sarcocystis that cause muscular sarcocystosis in human and non-human primates. Other species of Sarcocystis are known to cycle among snakes and rodents, but have been poorly characterized in the USA and elsewhere. Although neurological sequalae are known for certain species of Sarcocystis, no such neurological symptoms are known to typify parasites that naturally cycle in rodents. Here, sporocysts of a species of Sarcocystis were found in the intestinal contents of a rat snake (Pantherophis alleghaniensis) from Maryland, USA. The sporocysts were orally infective for interferon gamma gene knockout (KO) mice, but not to Swiss Webster outbred mice. The KO mice developed neurological signs, and were necropsied between 33 and 52 days post-inoculation. Only schizonts/merozoites were found, and they were confined to the brain. The predominant lesion was meningoencephalitis characterized by perivascular cuffs, granulomas, and necrosis of the neuropil. The schizonts and merozoites were located in neuropil, and apparently extravascular. Brain homogenates from infected KO mice were infective to KO mice and CV-1 cell line. DNA extracted from the infected mouse brain, and infected cell cultures revealed the highest identity with Sarcocystis species that employ snakes as definitive hosts. This is the first report of Sarcocystis infection in the endangered rat snake (P. alleghaniensis) and the first report of neurological sarcocystosis in mice induced by feeding sporocysts from a snake. These data underscore the likelihood that parasites in this genus that employ snakes as their definitive hosts constitute an ancient, globally distributed monophyletic group. These data also raise the possibility that neurological sequalae may be more common in intermediate hosts of Sarcocystis spp. than has previously been appreciated.