Equine viral arteritis in newborn foals: clinical, pathological, serological, microbiological and immunohistochemical observations.

This research article discusses the occurrence and examination of two separate epidemics of equine arteritis virus (EAV) in newborn foals. The researchers provide an in-depth analysis of the clinical, pathological, immunohistochemical, serological, and microbiological findings from the study.

Study Setting and Epidemics

The researchers investigated two separate outbreaks of equine arteritis virus:

• Outbreak A came about at a commercial Standardbred breeding facility. Standardbred horses are a popular breed used for harness racing.
• Outbreak B unfolded amongst a group of horses used for research purposes.

Clinical Observations

Although distinct in setting, both epidemics presented remarkable clinical similarities:

• The newborn foals exhibited severe clinical signs, primarily associated with the respiratory tract.
• Foals, which survived for more than 24 hours past infection, showed signs of fever, leucopenia (reduction in the number of white blood cells), and/or thrombocytopenia (lower than normal platelet count).

Pathological Findings

On gross pathology and histopathology, the researchers made the following findings:

• The most common gross pathological changes were limited to the respiratory tract.
• Under histopathological investigation, frequent findings included interstitial pneumonia (type of inflammatory response in the interstitium of the lung), lymphocytic arteritis (inflammation of the arteries with lymphocyte infiltration), and periarteritis with fibrinoid necrosis of the tunica media (inflammatory changes around the artery leading to death of arterial cells).
• Renal tubular necrosis, the death of cells that form the tubes of the kidneys, was observed in two of the foals.

Microbiological and Immunohistochemical Observation

For the detection and diagnosis of the EAV, the researchers employed an integrated approach of immunoperoxidase histochemistry and virus isolation:

• Immunoperoxidase histochemistry is a staining technique used to visualize the presence and location of specific proteins in tissue.
• Virus isolation refers to the process of isolating a virus from an infected host.
• With the combination of both methods, they were able to definitively diagnose all cases of the EAV in the studied foals.