The same genotype of Sarcocystis neurona responsible for mass mortality in marine mammals induced a clinical outbreak in raccoons (Procyon lotor) 10 years later

Authors: GUPTA, ADITYA - Oak Ridge Institute For Science And Education (ORISE); DUNCAN, MARY - St Louis Zoo; ARAUJO, LARISSA - Oak Ridge Institute For Science And Education (ORISE); Kwok, Oliver; Rosenthal, Benjamin; Khan, Asis; Dubey, Jitender

Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2023
Publication Date: 12/9/2023
Citation: Gupta, A., Duncan, M., Araujo, L., Kwok, O.C., Rosenthal, B.M., Khan, A., Dubey, J.P. 2023. The same genotype of Sarcocystis neurona responsible for mass mortality in marine mammals induced a clinical outbreak in raccoons (Procyon lotor) 10 years later. International Journal for Parasitology. 53(14):777-785. https://doi.org/10.1016/j.ijpara.2023.08.001.
DOI: https://doi.org/10.1016/j.ijpara.2023.08.001

Interpretive Summary: Parasites in the genus Sarcocystis impair livestock wildlife health and can threaten food safety. Such parasites naturally cycle between carnivorous hosts and the herbivores upon which they prey. Therefore, USDA researchers endeavor to understand which of these parasites occur in food animals and seek to illuminate the diversity and relationships among parasites occurring in wildlife. Here, they shed more light on one of these parasites (Sarcocystis neurona) previously known to cause a neurological disease in horses (Equine Protozoal Encephalitis, or EPM). Horses, and other animals such as raccoons, acquire this infection when ingesting food or water contaminated with the feces of opossums. Here, USDA researchers investigated an outbreak that killed dozens of racoons, supplementing traditional diagnostic criteria with novel molecular diagnostic tools. They demonstrated Sarcocystis neurona as the cause for these fatal and life-threatening cases of disease. The continued lack of evidence for human susceptibility to Sarcocystis neurona provides some relief for those concerned with public health. These results will be of interest to veterinarians, wildlife biologists, and zookeepers.

Technical Abstract: Here, we report the first molecularly confirmed outbreak of clinical Equine Protozoal Myeloencephalitis induced by infections of Sarcocystis neurona in naturally infected raccoons. The protozoan Sarcocystis neurona is an important cause of a serious neurological syndrome in horses called Equine Protozoal Myeloencephalitis (EPM). It also causes mortality in many species of animals, especially marine mammals. The North American opossum (Didelphis virginiana) and the South American opossum (D. albiventris) are its known de'nitive hosts. Several other animal species are its intermediate or aberrant hosts. The raccoon (Procyon lotor) is considered the most important intermediate host for S. neurona in USA. Opossums become infected by consuming S. neurona sarcocysts encysted in muscles of intermediate hosts. More than 50% of raccoons in the USA have sarcocysts in their muscles, however, clinical EPM disease in raccoons is rare. Here, we report an outbreak of an EPM-like neurological disease in raccoons. In 2014, 38 free-living raccoons were found dead or moribund on the grounds of the Saint Louis Zoo, Missouri. Moribund individuals were weak, lethargic, and mildly ataxic; several with oculo-nasal discharge. Seven raccoons were found dead and 31 were humanely euthanized. Postmortem examinations were conducted on nine raccoons. Neural lesions compatible with acute sarcocystosis were detected in eight raccoons. The predominant lesions were meningoencephalitis and perivascular mononuclear cells. Histologic evidence for the Canine Distemper Virus was found in one raccoon. Schizonts and merozoites were present in the encephalitic lesions of four raccoons. Mature sarcocysts were present within myocytes of five raccoons. In six raccoons, S. neurona schizonts and merozoites were confirmed by immunohistochemical staining with S. neurona-specific polyclonal antibodies. Viable S. neurona was isolated from the brains of two raccoons by bioassays in interferon gamma gene knockout mice (KO) and in cell cultures seeded directly with raccoon brain homogenate. Molecular characterization of DNA isolated from bradyzoites released from sarcocysts in a naturally infected raccoon (no. 68), confirmed the presence of S. neurona in both the brain and muscle of KO mouse inoculated with brain homogenate of this same raccoon, as judged by sequences of 18S rRNA, 28S rRNA, COX1, ITS-1, RON1, RON2, GAPDH1, ROP20, SAG2, SnSRS21 and TUBA1 markers. The identity of Sarcocystis species in raccoons is discussed.