Virulence of the V592 isolate of equid herpesvirus-1 in ponies.

The research investigates the severity of the V592 strain of equid herpesvirus-1 (EHV-1) in ponies. It reveals that this particular virus strain, first sourced from a fetus during an epidemic of abortions, shows low virulence when studied in infection trials, but causes mild illness and virus shedding in ponies.

Study Design and Participants

• The study involved five Welsh Mountain pony mares and one foal. The chosen creatures were deliberately exposed to the V592 strain of EHV-1 either intranasally or through aerosol.

Observations and Findings

• All the six ponies started shedding the virus from their nasopharynx (the area behind the nose and above the throat) after being infected. This was accompanied by viraemia (presence of virus in the blood) that was noted from the seventh day after the infections began.
• Mild rhinitis (inflammation of nasal mucous membrane) and bronchiolitis (inflammation of the bronchioles) were observed in the adult ponies.
• Viral antigens, that are substances capable of inducing specific immune responses, were found in damaged epithelial cells in the nose and bronchioles, and occasionally in specific white blood cells in lymph nodes associated with the respiratory tract.
• No viral antigens were found in the mares’ vascular endothelium (cells lining the blood vessels). However, vasculitis (inflammation of the blood vessels) was observed in a small number of blood vessels in the lung region of a mare tested on day 10 post-infection.
• In contrast, the foal exhibited more localized respiratory lesions, inclusive of vasculitis and infection of the vascular endothelium. The foal also suffered from a localized inflammation affecting the olfactory lobes of the brain, with the virus expressing itself in damaged olfactory neurons and microglia (a type of neuroglia cell).

Interpretation and Implications

• The results suggest that the relatively low virulence (ability to cause disease) of the V592 strain may be related to its lesser degree of endotheliotropism (affinity for the cells lining the blood vessels) compared to the highly virulent Ab4 and Army 183 EHV-1 isolates.
• The study also indicates that this endotheliotropism might be influenced by the host’s immune response. This provides valuable insights into the behavior of this virus strain and could influence the direction of future research and treatment strategies for EHV-1 infections.