Sarcocystis neurona, Neospora spp. and Toxoplasma gondii infections in horses and equine protozoal myeloencephalitis (EPM): five decades of personal experience, perspectives, and update

Authors: Dubey, Jitender

Submitted to: Parasitology
Publication Type: Literature Review
Publication Acceptance Date: 11/29/2021
Publication Date: 3/9/2022
Citation: Dubey, J.P. 2022. Sarcocystis neurona, Neospora spp. and Toxoplasma gondii infections in horses and equine protozoal myeloencephalitis (EPM): five decades of personal experience, perspectives, and update. Parasitology. https://doi.org/10.1017/S0031182021002055.
DOI: https://doi.org/10.1017/S0031182021002055

Interpretive Summary: Coccidia are a group of single celled organisms that cause severe illness in nanimals and humans. Eimeria, Sarcocystis, Neospora, Cyclospora, Cryptosporidium, and Toxoplasma are members of the group coccidia. Infections due to Sarcocystis are widely prevalent in livestock and there are more than 200 species in the genus Sarcocystis. While most species of Sarcocystis are host specific, and some species are zoonotic, Sarcocystis neurona has a wide host range causing severe illness in horses and is the leading cause of mortality in marine mammals in USA. S. neurona is a leading cause of a neurological illness in horses termed Equine Protozoal myeloencephalitis (EPM). Neospora is a common cause of abortion in cattle. One of the ARS researchers, J.P.Dubey, is a world authority on coccidian parasites and he led the research that first named the parasites Sarcocystis neurona and Neospora, cultivated them, and developed diagnostic tests. Here, he reviews, history and biology of EPM. This invited review should be of interest to biologists, veterinarians, and parasitologists.

Technical Abstract: Sarcocystis neurona, Neospora spp. and Toxoplasma gondii, are related protozoans;they were considered same parasite until 1970’s. Two of these parasites, S. neurona and Neospora spp. are associated with a neurological syndrome in horses, called Equine Protozoal Myeloencephalitis (EPM). The diagnosis and treatment of EPM are difficult. Most cases of EPM are related to S. neurona while only a few are due to Neospora spp. infections. There are 2 species of Neospora, N. caninum that has a wide host range and N. hughesi that has been found only in horses. Currently, T. gondii is not considered as cause of EPM in horses, although it causes neurological illness in many other hosts, including humans. The present review provides an update on history, life cycle, diagnosis, and treatment of these 3 infections in horses.