Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 30, 2001
Publication Date: N/A
Interpretive Summary: Sarcocystis neurona is a single-celled parasite. It causes fatal encephalitis in horses and several other species of animals. There is no suitable large animal model because it is difficult to infect horses with Sarcocystis neurona. Scientists at Beltsville Agricultural Research Center and Virginia Tech describe the utility of an immune-suppressed mouse to study S. neurona infection. These results will be useful to test drugs to treat S. neurona. Results will be of interest to biologists and parasitologists.
The dose-related infectivity of Sarcocystis neurona sporocysts and merozoites of 2 recent isolates of S. neurona was compared in gamma interferon knockout mice. Ten-fold dilutions of sporocysts or merozoites were bioassayed in mice, cell culture, or both. All 8 mice fed 1,000 sporocysts developed neurological signs with demonstrable S. neurona in their tissues. Of 24 mice fed low numbers of sporocysts (100, 10, 1), 18 became ill by 4 wk post- inoculation and S. neurona was demonstrated in their brains; antibodies (S. neurona agglutination test) to S. neurona and S. neurona parasites were not found in tissues of the 6 mice that were fed sporocysts and survived for > 39 days. One-thousand culture-derived merozoites of these 2 isolates were pathogenic to all 8 mice inoculated subcutaneously (s.c.). Of the 24 mice inoculated s.c. with 100, 10 or 1 counted merozoites, only 3 mice had demonstrable S. neurona infection; antibodies to S. neurona were not found in the 21 mice that had no demonstrable organisms. As few as 10 merozoites were infective for cell cultures. These results demonstrate that at least 1,000 merozoites are needed to cause disease in KO mice. Sarcocystis neurona sporocysts were infective to mice by the s.c. route.