There are many different kinds of herpesviruses out there, and some of them can be serious trouble for the animals in our care. Officials are now tracking a growing outbreak of neurological illness that’s spreading among working horses across the country.
On Monday, the Equine Disease Communication Center (EDCC) issued its latest update on the outbreak of equine herpes myeloencephalopathy, or EHM. At least 29 cases of EHM have been identified in seven states so far. The outbreak appears to have originated from a rodeo and racing event held in Texas earlier this month.
A troublesome virus
EHM is caused by an infection of the equine herpesvirus-1 (EHV-1).
EHV-1 is a ubiquitous and highly contagious germ. Most horses catch it at some point in their lives, usually through direct contact with other horses, airborne transmission across short distances, and indirect contact with contaminated surfaces or even people’s hands and clothing. Most of the time, EHV-1 only causes acute respiratory illness, after which it goes silent and lies dormant in the body (a feature common to many herpesviruses). But sometimes, the virus can travel to the brain and spinal cord, inflaming blood vessels and triggering dangerous blood clotting, which results in EHM.
EHM is most often caused by strains of EHV-1 that are more likely to produce the neurological form of infection, but a respiratory strain of EHV-1 can rarely cause EHM as well. The virus can also reactivate from dormancy and spread to the nervous system, triggering EHM.
The outbreak, according to the EDCC, began sometime during the Women’s Professional Rodeo Association (WPRA) World Finals and Elite Barrel Race event held in Waco between November 5 and 9. Several horses that attended the event developed EHM, prompting a widespread alert from animal health and racing horse officials in several states. Last week, officials chose to cancel the remainder of the Barrel Futurities of America (BFA) World Championship scheduled to be hosted in Oklahoma after two horses in the state that recently traveled to Waco came down with EHM.
At this point, the potential impact of this outbreak is still unclear, though it could be vast. One of the largest known outbreaks of EHM/EHV-1 began in 2011 at a cutting horse event in Ogden, Utah, which exposed the virus to roughly 2,000 horses in 19 states, infected at least 90 horses, and killed 13.
“The extent of this EHV-1 outbreak is not yet fully known. Presentation of EHV-1 in these horses has been acute with rapid progression and high clinical severity. A concerning number of mortalities in horses suspected to have EHM have been reported,” said the Texas Animal Health Commission in an update last week.
A known threat
As worrying as this outbreak is, most cases of EHM are not fatal, especially with prompt detection and supportive treatment. There is a vaccine for EHV-1, which is used to prevent the respiratory form of the infection and the risk of miscarriage in pregnant horses. Though the vaccine doesn’t directly prevent EHM, it may help curb the spread of outbreaks by reducing the potential viral load of infected horses.
For now, officials are coordinating with the WPRA event sponsors, horse owners who attended the WPRA events, and veterinarians to track and stop the spread of the outbreak. Vets who believe they’ve encountered a potential case are being advised to submit a report to the EDCC.
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