The Equine Disease Communication Center is monitoring an outbreak of equine herpesvirus myeloencephalopathy (EHM), the neurologic form of equine herpesvirus-1 (EHV-1), that originated at the Women’s Professional Rodeo Association (WPRA) World Finals and Elite Barrel Race event in Waco, Texas, on Nov. 5-9.

The EDCC has just confirmed 12 new cases associated with this outbreak. The new cases are all located in Texas: 

• Erath County: One horse tested positive on Nov. 25. 
• Grimes County: One horse tested positive on Nov. 26. A second horse tested positive on Nov. 27.
• Jefferson County: Two horses tested positive. 
• Wise County: One horse tested positive on Nov. 26. 
• Ellis County: One horse tested positive on Nov. 29. 
• McLellan County: One horse tested positive. 
• Lee County: One horse tested positive on Nov. 27. 
• Montgomery County: Two horses tested positive. 
• Wharton County: One horse tested positive for EHM, and two horses are suspected to be positive for respiratory EHV-1 disease.

Previously reported cases include:

Texas

• McLennan County: Two horses. 
• Montgomery County: Three horses. 
• Wharton County: One horse. 
• Bell County: One horse. 
• Fort Bend County: One horse. 
• Erath County: Four horses. 
• Wise County: One horse. 
• Hood County: One horse. 
• Parker County: One horse. 
• Randall County: One horse. 
• Lee County: One horse. 
• Waller County: Four horses. 
• Harris County: One horse. 

Oklahoma

• Logan County: Two horses. 
• Mayes County: One horse. 
• Oklahoma County: Two horses. 
• Love County: One horse. 
• McClain County: One horse. 
• Payne County: One horse. 

Louisiana

• East Baton Rouge Parish: Three horses. 

Colorado

• Larimer County: One horse. 

New Mexico

• Dona Ana County: One horse. 
• Eddy County: Two horses. 

Washington

• Spokane County: Two horses. 

Arizona

• Maricopa County: Three horses. 

South Dakota

• Hyde County: One horse. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM.

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.