Concern grows over aggressive neurological equine herpes strain

A mare in Marion, Florida, has tested positive for the potentially deadly form of the virus, prompting strong cautionary statements from veterinary officials.
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A mare in Marion, Florida has tested positive for the neurological strain of equine herpesvirus, type 1 (EHV-1), raising concerns that a very aggressive strain of the virus currently circulating in Europe may eventually make its way to the United States. 

Microscopic image of EHV virus

EHM occurs when EHV-1 attacks the cells lining the central nervous system, damaging blood vessels serving the brain and spinal cord.

EHV-1 most often causes mild-to-moderate respiratory illness (rhinopneumonitis), but the infection occasionally leads to the life-threatening neurologic disease equine herpesvirus myeloencephalopathy (EHM). The mechanisms through which EHV-1 produces neurologic disease are not yet understood. 

Learn more: Read "When EHV-1 Turns Deadly." 

The emergence of a very aggressive strain of neurologic EHV-1 from Spain lead the Fédération Équestre Internationale (FEI), the international governing body of Olympic equestrian disciplines, to cancel nearly all competitions in mainland Europe earlier this week until at least March 28.

FEI Secretary General Sabrina Ibáñez said in a statement at the time “...this EHV-1 outbreak is probably the most serious we have had in Europe for many decades and our decision is based on clearly identified epidemiological risk factors. 

"This strain of EHV-1 is particularly aggressive and has already caused equine fatalities and a very large number of severe clinical cases. We need to keep our horses safe. We are also aware that a large number of horses left the venue in Valencia without an official health certificate, meaning they had an unknown health status. Some horses were already sick, and the risk of transmission from these horses is a major concern."

Click here to read the full press release about the FEI cancellations.

There is no vaccine that specifically protects against EHM, so biosecurity is a crucial part of prevention. EHV-1 spreads from horse to horse through nasal discharge or aerosol droplets. Humans can spread the virus via contaminated hands, clothing and equipment.

The 8-year-old mare in Florida developed ataxia and weakness in her hind limbs on March 1 and the diagnosis of neurologic EHV-1 was confirmed on March 3, according to the Equine Disease Control Communication Center (EDCC). Although it has not been confirmed that the mare has the more aggressive strain, veterinary officials are encouraging everyone in the equestrian community to be vigilant, cautious and careful. The following statement appeared on the EDCC website: 

As of March 3, 2021, the affected horse continues to be treated in a separate isolation facility. No additional EHV-1 cases have been detected. The Division of Animal Industry placed the premises under quarantine and immediately began a disease investigation. Additional movement requirements or restrictions have not been imposed by Florida or any other states at this time. We are advising horse owners and trainers to contact the venue of destination for any additional requirements prior to travel.

However, in light of the recent EHV-1 outbreak in Europe, we are encouraging all facilities to isolate horses importing into Florida from the affected regions in Europe and enact strict biosecurity measures to include monitoring the horse’s health and taking temperatures twice per day for at least 14 days. We are asking all those in the equine community to practice prudent biosecurity on their farm and to report any suspected cases of EHV-1.

For reporting, call (850) 410-0900 Monday through Friday 8:00 a.m. – 5:00 p.m. and 1-800-342-5869 after hours and weekends or email RAD@FDACS.gov. The Florida Department of Agriculture and Consumer Services will continue to work with the affected premises management, owners, and veterinarians to ensure proper safeguards are taken to prevent further spread of the disease.

There are 53 potentially exposed horses at the Florida stable.

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