Equine herpes virus (EHV) is a difficult disease to control. “It is speculated that 80 to 90 percent of horses become infected with EHV by 2 years of age, and up to 90 percent of adult horses are latent carriers,” says D. Craig Barnett, DVM, senior equine technical services specialist, Veterinary Services, Intervet Inc. These statistics are scary given the recent EHV outbreaks that have claimed several equine lives across state lines.

Researchers have identified five types of EHV, but EHV-1 and EHV-4 are the most common and are the only types for which there are vaccines. EHV-1 can cause severe respiratory disease, including rhinopneumonitis (“rhino”), abortion and neurological problems, whereas EHV-4 is primarily limited to respiratory complications. Currently, there are no vaccines labeled for protection against the neurological form of EHV-1, which can be deadly.

In latent carrier horses, EHV lies dormant, but can become active during times of stress or poor health, which is why the disease is so hard to control. However, good horsekeeping practices, including vaccination that helps reduce viral shedding from infected horses, can help decrease risk of disease.