In 2006, a number of racetracks, private veterinary clinics and university teaching hospitals outside of California were shut down to limit the spread of Equine Herpesvirus-1 infection. There were additional cases in 2007. Information on EHV-1 will continue to be posted on this site to provide awareness to California horse owners regarding the infection. Questions may be directed to Dr. Nicola Pusterla or Dr. David Wilson, UC Davis Veterinary Medical Teaching Hospital, (530) 752-0290.

What is Equine Herpesvirus-1?

Equine herpesvirus 1 (EHV-1) is one of a large group of DNA viruses causing potentially serious disease in horses and other species. EHV-1 has two forms - one that causes abortion in mares and one that causes respiratory infection and neurological symptoms. The most recent outbreaks of concern have involved the EHV-1 respiratory/neurological form of the virus.

EHV-1 is contagious and is spread by direct horse-to-horse contact, by contaminated hands, equipment and tack, and, for a short time, through aerosolization of the virus within the environment of the stall and stable.

What are the Clinical Signs of EHV-1?

The initial clinical signs of the infection may be nonspecific and include fever of 102°F or greater. Fever may be the only abnormality observed. Other presenting signs may be combinations of fever and respiratory symptoms of nasal discharge and cough. Some horses have reddish mucous membranes.

Horses with the neurological form of EHV-1 can soon become uncoordinated and weak and have trouble standing. Difficulty urinating and defecating may also occur. Often the rear limbs are more severely affected than the front.

Signs of brain dysfunction may occur as well, including extreme lethargy and a coma-like state. The incubation period for the infection is 2 to 8 days. Once a fever occurs, clinical signs can progress to nervous system involvement over the next 1 to 7 days.