Pathologic features of horses given avirulent equine arteritis virus intramuscularly.

This study aimed to investigate the pathologic features of horses after being administered an avirulent, or non-disease causing, strain of the equine arteritis virus via intramuscular injection.

Study Design

• The experiment involved twenty horses that didn’t have antibodies to the equine arteritis virus, indicating they were not previously exposed to this virus.
• These horses were inoculated (or vaccinated) intramuscularly with the virus.

Observations and Results

• None of the horses displayed clinical signs of the disease after the vaccination.
• Six of the horses experienced a mild and temporary febrile (characterized by fever) reaction. Half of these horses were reported to have been in poor health before the inoculation.
• A mild drop in lymphocyte count (lymphopenia), which are critical cells for immune responses, was observed in six horses. Again, two of these horses were in poor health before getting inoculated.
• Post-mortem examinations revealed minor lesions or damage in the lymph nodes of six horses, and three of these were in poor condition before vaccination.
• The highest concentrations of the virus were found in the lymph nodes, specifically between day 3 and 8 post-vaccination.
• Lower concentrations of the virus were detected in other organs such as the spleen, liver, and kidneys. The virus was also present in the abdominal fluid, fluid in the pleural cavity surrounding the lungs, and the lungs themselves, as well as in the urine.
• However, the virus was not detected in the brain, nasal tract, or serum (the clear part of the blood).

Major Takeaways

• This study provided critical findings on the pathologic effects of the equine arteritis virus, demonstrating that even an avirulent strain of the virus can induce mild responses and distribute within several organs in horses.
• Further studies are necessary to understand the long-term effects and the potential for disease if such a virus would mutate and become virulent, or disease-causing.