Location: Animal Parasitic Diseases LaboratoryTitle: Testing the Sarcocystis neurona vaccine using an equine protozoal myeloencephalitis challenge model Author
|Saville, William - The Ohio State University|
|Marsh, Antoinette - The Ohio State University|
|Reed, Steven - Rood And Riddle Equine Hospital|
|Keene, Robert - Boehringer Ingelheim Pharmaceuticals|
|Howe, Dan - University Of Kentucky|
|Morrow, Jennifer - Equine Diagnostic Solutions Llc|
|Workman, Jeffrey - The Ohio State University|
Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2017
Publication Date: 10/1/2017
Citation: Saville, W., Dubey, J.P., Marsh, A., Reed, S., Keene, R., Howe, D., Morrow, J., Workman, J. 2017. Testing the Sarcocystis neurona vaccine using an equine protozoal myeloencephalitis challenge model. Veterinary Parasitology. 247:37-41. http://dx.doi.org/10.1016/j.vetpar.2017.09.012.
Interpretive Summary: Toxoplasma and Sarcocystis are related single celled parasites of livestock and humans. While Toxoplasma has long been recognized to cause neurologic disease in many warm blooded hosts, a species of the related genus Sarcocystis, S. neurona causes fatal neurological disease in horses called Equine Protozoal Myeloencephalitis (EPM) , marine mammals, and several other hosts. A vaccine consisting of killed S. neurona was developed commercially but was later withdrawn. In the present study, authors tested the efficacy of the vaccine in horses experimentally infected with S. neurona and determined that the vaccine did not prevent development of clinical signs of EPM. The results will be of interest to biologists, veterinarians, and parasitologists.
Technical Abstract: Equine protozoal myeloencephalitis (EPM) is an important equine neurologic disorder, and treatments for the disease are often unrewarding. Prevention of the disease is the most important aspect for EPM, and a killed vaccine was developed for just that purpose. Evaluation of the vaccine has been hampered by lack of post vaccination challenge. The purpose of this study was to determine if the vaccine could prevent development of clinical signs after challenge with Sarcocystis neurona sporocysts in an equine challenge model. Seventy horses that were negative for antibody to S. neurona and were neurologically normal were randomly assigned to vaccine or placebo groups and divided into a short-term duration of immunity (study 1) and long term duration of immunity (study 2) studies. Sporocysts used for the challenge were generated in the opossum/raccoon cycle isolate SN 37-R. Study 1 horses received an initial vaccination and a booster, and were challenged 34 days post second vaccination. Study 2 horses received a vaccination and 2 boosters and were challenged 139 days post third vaccination. All horses in study 1 developed neurologic signs (n=30) and there was no difference between the vaccinates and controls (0.7683). All but 4 horses in study 2 developed detectable neurologic deficits. The neurologic signs, although not statistically significant were worse in the vaccinated horses (P=0.1559). In these 2 studies, vaccination with the S. neurona vaccine failed to prevent development of clinical neurologic deficits.