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Equine Herpesvirus-1 Alert
Outbreaks Noted in Wisconsin, Florida & California

Update, February 7, 2007: Three new cases of EHV-1 at Los Alamitos racecourse have been confirmed. The cases are from one barn and movement restrictions are in place there. Meanwhile, in Connecticut, three horses have tested positive for EHV-1 and have neurologic signs. The horses are based at the University of Connecticut, where several other exposed horses are showing respiratory signs. The herd of 72 is under quarantine.

Previously Reported on February 4: Three horses in Jefferson County, Wisc., have been confirmed positive for equine herpesvirus-1 (EHV-1), according to a statement written by Scott Austin, DVM, Dipl. ACVIM, of the Wisconsin Equine Clinic, and released on the Wisconsin Horse Council Web site. Two horses, one of which tested negative for the virus, displayed neurologic signs and were euthanatized. As well, several quarter horses at Los Alamitos Racetrack in California, and a number of dressage and jumping horses in Wellington, Florida have tested positive for EHV-1.

What is EHV-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.

It is important to note that 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 the air environment of the stall and stable.

Clinical Signs
The initial clinical signs of the infection may be nonspecific and include fever of 102ºF 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.

Isolation Imperative
Isolation of sick horses and early determination of the cause of their symptoms is very important. It is prudent to determine if the horse has been around horses that may have been in a place where EHV-1 has been documented to occur. Infections other than EHV-1 can also spread by horse-to-horse contact, so keeping a horse with a fever isolated is a very good practice in any case.

If your horse develops fever, respiratory signs or neurological signs, immediately notify your veterinarian and do not move the horse or horses in the immediate area. Alert those who have horses in the adjacent area to cease all movement of horses in and out of the facility until a diagnosis is confirmed by testing. If horses are exposed and then travel to a new stable or show, the infection can spread to other horses at that new location.

EHV-1 does not persist in the environment for a long time, but disinfection of premises, stalls, trailers and so forth is indicated. If you handle a horse with EHV-1 and don’t wash hands or change clothing, you may spread the infection to other horses. A solution of 1 part chlorine bleach to 10 parts water is effective for decontaminating equipment and environment.

Horses with high fevers and/or clinical signs of coughing or mild nasal discharge, with or without neurologic symptoms, should be tested for EHV-1 by PCR diagnostics if other explanations for these signs of disease are not apparent. Detecting a positive PCR for EHV-1 in these circumstances may warrant some degree of patient isolation and limited movement of exposed horses.

Vaccinations
While there are several vaccines available for protection against both respiratory and abortogenic forms of EHV-1, at this time there is no equine vaccine that has a label claim for protection against the neurological strain of the virus. Consult your veterinarian for further guidance if you are considering the use of EHV-1 vaccines.