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ALERT – Equine Herpes Information

Animal Health Branch veterinarians are investigating a report of one (1) horse in Orange County confirmed positive for neuropathogenic strain of Equine Herpes Virus-1. Horses on the premises where the affected horse is located are under quarantine with no movement of horses on or off of the property. All horses on the property are being monitored at this time and the investigation is ongoing. 

What is EHV-1?

EHV-1 (equine herpesvirus-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 above cited outbreaks have involved the EHV-1 respiratory/neurological form of the virus causing a condition known as Equine Herpes Myeloencephalopathy (EHM).

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 neurological disease caused by EHV-1 infection 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 of EHV-1 infection is HIGHLY VARIABLE, depending on the host, on the virulence of the virus, and on environmental and other factors such as stress. The AVERAGE incubation period is 4 to 7 days, with the majority of cases being 3 to 8 days, but with some taking up to 14 days. When neurological disease occurs, it is typically 8 to 12 days after the primary infection involving fever. In most cases, horses exposed to EHV-1 will develop a fever and possibly nasal discharge and then go on to recover.

EHV-1 How to Handle a Sick Horse

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