Utilization of stress in the development of an equine model for equine protozoal myeloencephalitis.

This research paper involves the development of an equine model for Equine Protozoal Myeloencephalitis (EPM), a disease in horses caused by a specific protozoa called Sarcocystis neurona. The study assesses the role of stress, specifically transport stress, in the progression and severity of the disease.

Objective and Methodology

• The primary aim of the research was to enhance the understanding of Equine Protozoal Myeloencephalitis’ pathogenesis, a difficult-to-diagnose and treat disease in horses caused by Sarcocystis neurona.
• In order to achieve this, the study evaluates the role of transport stress, which prior epidemiology studies have identified as a risk factor for EPM.
• The researchers collected sporocysts from feral opossums and used Interferon-gamma gene knockout mice for bioassay to isolate the Sarcocystis neurona sporocysts. 80,000 viable ones were administered to each participating horse.

Experiment Design

• The study included twelve S. neurona antibody-negative horses, segregated into four groups.
• The horses in group 1 were administered sporocysts upon their arrival at the study location (thus introducing transport stress), group 2 horses received sporocysts 14 days post-acclimatization, and group 3 horses were given sporocysts and dexamethasone 14 days after acclimatization.
• Group 4 consisted of control horses who did not receive sporocysts.

Results

• All horses that were given sporocysts (groups 1-3) developed S. neurona antibodies in their blood and cerebrospinal fluid (CSF). They also exhibited clinical signs of neurologic disease, indicating successful infection.
• Horses in group 1, subjected to transport stress, displayed the most severe clinical signs, while the least severe signs were observed in horses treated with dexamethasone (group 3).
• Post-mortem examinations and the collected brain tissues showed no direct evidence of S. neurona infection. Still, they presented lesions that were compatible with S. neurona infection, indicating the possible cause of the neurologic disease.

Conclusion

• The study suggests that stress can play a significant role in EPM’s pathogenesis, and additional factors such as transport stress should be included in creating reliable equine models for this disease.
• The results also imply that horses might clear S. neurona naturally over time, potentially explaining why many horses have CSF antibodies against S. neurona but do not develop EPM.