Neurological Equine Herpes Virus Type-1 Alert

Livestock Update, March 2007

Scott Pleasant, Extension Equine Specialist – Veterinary Medicine, VA Tech
Celeste Crisman, Extension Equine Specialist - Youth, VA Tech

Several states, including Virginia, have recently experienced cases of the neurological form of equine herpes virus type-1 (EHV-1). These outbreaks have resulted in the death of several horses and the quarantine of a number of racetracks, veterinary clinics, show grounds, and farms. Concern has been voiced that the neurological form of EHV-1 is increasing in prevalence and/or morbidity and mortality, and that outbreaks will become more common. The purpose of this update is to provide awareness to Virginia horse owners and to encourage employment of management practices to protect against this and other contagious diseases.

Equine herpes virus type-1 is virus that can cause several different problems in horses including abortions in mares, birth of weak foals, respiratory disease in young horses, and paralytic neurological disease. EHV-1 is common throughout the world and almost all horses over two years of age have been exposed to the virus. The virus has the ability to develop into unapparent, latent infections with the capacity for reactivation/shedding during times of stress. This ability to reside as a silent and persistent infection provides a reservoir of the virus for continual transmission.  EHV-1 presents no known health threat to humans.
 
The incubation period for EHV-1 is 1-10 days. Typical clinical signs include fever and mild respiratory disease.  Affected horses shed the virus in nasal secretions. This shedding usually occurs for 7-10 days after the onset of clinical signs (but can persist much longer in some cases). The disease is highly contagious. The most common method for transmission of the virus between horses is the aerosol route (airborne). Indirect transmission is also common and can occur via contaminated hands, clothing, equipment, etc. Aborted fetuses and associated placental membranes may be significant sources of infection as well. It has been estimated that the virus may survive up to one week in a moist environment protected from sunlight.

Horses with the neurological form of EHV-1 become weak and uncoordinated. Difficulty urinating and defecating may also occur. Horses that become recumbent have a very poor prognosis for survival. Treatment for EHV-1 is supportive and tailored to the specific case.

Recently, a mutation of the EHV-1 virus has been linked with the outbreaks of the neurological form of the disease. The mutation appears to give the virus an enhanced ability to multiply (more virus circulates in the horse’s body) and infect cells of the nervous system. At this time, it is not known whether the identified mutation arises newly with each outbreak, or whether horses are now carrying the mutant virus in the latent state.  Currently, there is no vaccine that has a label claim for protection against the neurological strain of the virus. Your veterinarian should be consulted for guidance on the use of EHV-1 vaccines.

To help prevent and control EHV-1 and other contagious disease outbreaks on your farm, the following management practices are recommended:

• Minimize visitors to your farm, barn, and horses. When entering or exiting a barn, disinfect footwear using a foot bath and wash hands (with soap and water or use a dry disinfectant).
• After handling individual horses, wash hands.
• Don’t share equipment or stalls among horses.
• New horses should be received and maintained in an isolation barn or paddock for 30 days. The 30-day quarantine period helps ensure that horses that are incubating or shedding a contagious disease are not inadvertently introduced into the farm population. The isolation area should be physically separated from resident horses. Separate equipment and preferably separate personnel should be used to take care of the isolated horses. If separate personnel are not available, the isolated horses should be tended to after the other horses on the farm. During the 30-day quarantine period, horses should be monitored for signs of contagious disease. Rectal temperatures should be taken at least once daily.  If an increased rectal temperature is noted, a veterinarian should be consulted.
•  Resident horses returning from events should ideally be isolated and monitored for signs of contagious disease for at least 10 days. If this is not possible, returning horses should have rectal temperatures taken at least once daily for 10 days. Immediately isolate any horse that develops a fever.
• Any resident horse that becomes ill with a potentially contagious disease should be promptly isolated. Isolation should continue for at least 10 days past resolution of symptoms.
• Take rectal temperatures of horses that were exposed to a sick horse at least once daily. Promptly isolate any horse that develops a fever.
• Stalls and equipment that have been used on sick horses should be thoroughly cleaned and disinfected.

Additional information about neurological equine herpesvirus-1, biosecurity practices, and updates on the current situation in Virginia can be found at:

 http://www.aphis.usda.gov/vs/ceah/cei/taf/emergingdiseasenotice_files/ehv.pdf
 
 USDA Biosecurity — The Key to Keeping Your Horses Healthy

http://www.vdacs.virginia.gov/

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