Which of the following is most likely to be an equine herpesvirus infection?

• A. A severe and highly fatal respiratory disease that affects horses of all ages
• B. A mild respiratory disease that affects young animals that have been in close contact
• C. A rapidly spreading, severe respiratory disease that affects large numbers of young horses
• D. A severe respiratory disease that affects only immunodeficient foals

Answer: (B)

Equine herpesvirus infections most often present as mild upper-respiratory disease in foals and yearlings that are kept together in groups. This pattern is typical of EHV-4, which spreads through nasal secretions and aerosols and usually causes short-lived signs such as a low-grade fever, mild nasal discharge, and coughing in young horses in close contact. While EHV-1 can lead to more severe outcomes like abortion in pregnant mares or neurologic disease, those are not the common presentation described for a simple respiratory illness in young animals. The scenario described—mild respiratory disease in young horses in close contact—best matches an equine herpesvirus infection.