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Equine Herpes Virus-1 Alert
By California Department of Food and Agriculture Office of Public Affairs
A recent disease outbreak of Equine Herpes Virus-1 (EHV-1) has been traced to a shipment of horses from Europe and has resulted to date in the death of one horse in California and numerous other exposed horses around the country, including two horses in California that have developed mild clinical illness. Additionally, this outbreak and more EHV-1 related deaths have caused the shutdown of a major horse show in Florida. Outbreaks of EHV-1 have also significantly impacted major raceways and other equine operations in recent months. The cause of the disease outbreaks and deaths has been diagnosed as a neurological strain of EHV-1.
EHV-1 Update:
EHV-1 has two sub-types: one that may cause abortion in mares, and one that may cause both respiratory and neurological illness. The most recent outbreaks of concern have involved the respiratory/neurological form. Infection with this form may result in clinical illness ranging from mild to occasionally terminal. However, in many cases when horses are incubating the virus, fever in excess of 102° F may be the only observable sign of infection.
Stress and lack of previous exposure to the virus cause your horse to be much more susceptible to becoming clinically ill.
Currently, there is no equine vaccine that has a label claim for protection against the neurological strain of the virus.
It is virtually impossible at this time to know if horses in our native population have ever been naturally exposed to recently diagnosed strains of EHV-1 and subsequently developed any type of immunity to the virus.
At present, there is not a completely reliable test to “screen” a horse that is incubating the virus prior to shipping into a new location. This means that it is impossible for managers of public gatherings to “screen” out “EHV-1 incubating horses” from coming to their events.
Until more is known about the recently diagnosed strains of EHV-1 and their prevalence in the domestic horse population, avoiding the exposure of ones horses to new horses, especially horses known to have been recently exposed to EHV-1, is the best means for preventing an outbreak.
If horses are exposed to new horses, especially in stressful competitive environments, it is imperative that a monitoring plan is established under the advice of a veterinary practitioner that includes monitoring the horse’s temperature at least twice a day. Incubation of the virus after exposure ranges in most cases from 1 to 12 days, and the daily temperature monitoring should be maintained accordingly. Any spike in temperature should immediately be reported to a veterinarian for follow-up differential diagnosis. Horses that are diagnosed with EHV-1 should be isolated away from other horses for at least 21 days after the fever or any other clinical signs subside.
EHV-1 is not a regulatory disease in many states including California and, therefore, it is crucial to repeat that owners and trainers are advised to work very closely with their veterinary practitioner to develop a preventative plan that is right for their horse.
If you have further questions about EHV-1, refer to Web sites for CAHFS Laboratory and also the UC Davis Center for Equine Health:
