Alberta. Equine viral arteritis in a Thoroughbred filly.

This scientific research details a specific case study of a Thoroughbred filly horse that was infected with Equine Arteritis Virus (EAV) and subsequently euthanized due to severe clinical signs and an inability to respond to aggressive treatment. The pathological lesions observed and virus isolation confirmed this diagnosis.

Case Presentation and Clinical Signs

• A group of horses was transported from California to Alberta. One horse succumbed to severe pleuritis. Another horse, a three-year-old Thoroughbred filly, exhibited an aversion to food and appeared depressed.
• The filly displayed clinical signs suggestive of pleuritis and had a significant increase in band neutrophils. Initially, a liter of blood-tinged fluid was removed from each side of the thorax and various treatments were administered, including broad-spectrum antibiotics, mineral oil due to a lack of manure production, and nonsteroidal anti-inflammatory drugs.
• Despite treatment, the filly developed diarrhea and signs of shock, necessitating euthanasia.

Pathological Findings

• The autopsy revealed severe necrotizing colitis in the large intestine, with a significant thickening of the walls due to edema. Greyish yellow liquid filled the cecum and large colon.
• Microscopic examination showed a severe diffuse subacute necrotizing colitis with vascular thrombosis, numerous inflammatory cells, and fibrin in the underlying tissue. There was thrombosis of numerous blood vessels in the submucosa and lamina propria.
• There was a mild perivascular mononuclear cell infiltration in some kidney locations. No abnormalities were detected in the small intestine.

Virus Isolation and Identification

• The Equine arteritis virus (EAV) was isolated from a homogenate of liver and colon, successfully grown and confirmed in separate cell lines, utilizing a serum neutralization test with referential antiserum to EAV.
• EAV is an RNA virus from the Togaviridae family, it primarily affects horses, causing vasculitis in arteries, veins, and lymphatics. It can be transmitted via respiratory and venereal routes. Long-term carrier stallions play a crucial role in the virus’s perpetuation and spread.
• In areas where EAV is prevalent, horses exposed to infected animals should be segregated for three weeks to prevent further transmission. The use of a live virus vaccine is recommended as natural exposure provides lasting immunity.

Research Conclusion

• Based on serological studies, EAV is widespread in North America, but clinical disease manifestation is rare, and mortality rates are low in natural outbreaks.
• Due to the virus’s frailty outside its host, virus titers may decrease before death, making successful isolation challenging.
• The variable spectrum of symptoms resulting from vascular damage due to EAV complicates clinical diagnosis. Hence, virus isolation remains the only reliable method for achieving a definitive diagnosis.