Testing the Sarcocystis neurona vaccine using an equine protozoal myeloencephalitis challenge model.

This research investigates the effectiveness of a vaccine for equine protozoal myeloencephalitis (EPM), a common neurological disorder in horses. The vaccine was tested on horses in two studies of varied duration, followed by exposure to the disease-causing Sarcocystis neurona sporocysts. Unfortunately, the vaccine did not prevent the development of clinical neurologic deficits in the participating horses.

Detailed Explanation of the Research Paper

Introduction to EPM and the Vaccine

• Equine protozoal myeloencephalitis (EPM) is a significant neurological disorder affecting horses. Although there are treatment options available, they often produce unsatisfactory results.
• Given these circumstances, preventing the disease is of prime importance. A vaccine was previously designed for this exact purpose.
• The evaluation of the vaccine’s effectiveness was hindered due to the absence of a challenge post-vaccination until now.

Objective and Methodology of the Study

• The main aim of this research was to verify whether the developed EPM vaccine could prevent clinical signs following exposure to Sarcocystis neurona sporocysts – the disease-causing agents.
• The researchers utilized an equine challenge model, involving 70 horses that were free from S. neurona antibodies and had no neurological abnormalities.
• The horses were randomly split into control (placebo) and vaccine groups, and then further divided for two separate studies investigating short and long-term duration of immunity.
• The source of the sporocysts used for testing was an isolate called SN 37-R, cultivated within the lifecycle of opossums and raccoons.

Procedure and Results of the Two Studies

• In the first study (short-term immunity), horses received an initial vaccination and a booster, and then were challenged 34 days following the second vaccination.
• All horses in study #1 developed neurological symptoms, with no significant disparity between the vaccinated and control groups. This suggests the vaccine failed to provide short-term immunity against EPM.
• In the second study (long-term immunity), horses had a vaccination series of one initial shot and two boosters, followed by a challenge 139 days after the last booster.
• Almost all horses from study #2 (except four) displayed discernible neurological deficits. These symptoms, although statistically insignificant, were somewhat more pronounced in vaccinated horses, indicating no long-term immunity provided by the vaccine.

Conclusion

• The results from both studies were disappointing as the S. neurona vaccine did not prevent the lead-up of clinically observable neurological deficits in the horses, despite its intended purpose of doing so.