Equine herpes virus-1, a sometimes deadly virus that can cause myeloencephalopathy in some infected horses (Equine Herpesvirus Myeloencephalopathy or EHM), has surfaced at one horse farm in Union County, NJ, as reported by the New Jersey Department of Agriculture on March 20, 2018 and in theHORSE on March 21, 2018.
The second horse had an elevated temperature and was showing respiratory signs, but no neurological signs were noted by the attending veterinarian.
The first horse was moved into the isolation barn on the property last week and the property was placed under quarantine. The finding of another positive horse has reset the quarantine clock and will delay the release date another three days. These are the first reported EHV-1 cases in New Jersey in 2018.
As reported by the UK Gluck Equine Research Center, designated as a World Reference Center for EHV-1 and EHV-4:
Over the past decade there has been an unexpected increase in equine herpesvirus neurologic disease (equine herpesvirus myeloencephalopathy [EHM]) incidence. Previous research by other scientists suggests a significant percentage of EHM or paralytic herpes outbreaks are caused by a mutant strain. A single mutation has been identified in the gene encoding of the viral replication enzyme, which seems to confer the power of enhanced pathogenicity (a pathogen’s ability to cause disease in an organism) or neurovirulence to such strains.
New Jersey is not a novice in managing EHM outbreaks. As previously described, New Jersey Department of Agriculture in partnership with the New Jersey Racing Commission, private practitioners, horse trainers, and with assistance from USDA, issued and supervised a quarantine of horses boarding at Monmouth Race Track in October 2006 which lasted two months. See, Equine Herpes Virus Myeloencephalopathy-A Guide to Effective Response; and Infectious Diseases In Animals And Humans – What Is Your Legal Risk?
USDA publishes “A Guide to Understanding the Neurologic Form of EHV Infection” equine_herpesvirus_brochure_2009, and explains that “Equine Herpes Virus (EHV-1) infection in horses can cause respiratory disease, abortion in mares, neonatal foal death, and/or neurologic disease. The neurologic form of EHV-1 is called Equine Herpes Virus Myeloencephalopathy (EHM). The virus can spread through the air, contaminated equipment, clothing and hands.”
In USDA’s Equine Herpesvirus Myeloencephalopathy: Mitigation Experiences, Lessons Learned, and Future Needs, in which responders to the Monmouth Race Park quarantine were interviewed (including me):
Dr. Peter Timoney, Professor, University of Kentucky, Gluck Equine Research Center and Chair of the Infectious Diseases of Horses Committee of the United States Animal Health Association (USAHA), pointed out that ‘. . . within the past few years, a mutant of the wild-type of EHV-1 has been identified which evidence would indicate is very frequently associated with outbreaks of EHM. Also, this mutant has been identified among isolates of EHV-1 made prior to 2000. As the distribution of this virus mutant becomes more widespread in the equine population, the frequency and severity of outbreaks of EHM is likely to increase further unless measures to control its spread and occurrence of the disease can be developed.’
In addition to animal health issues, EHM outbreaks can result in lawsuits, as evidenced by the New Jersey Thoroughbred Horsemen’s Ass’n v. Alpen House U.L.C., 942 F.Supp.2d 497 (D.N.J. 2013), in which
Racehorse owners and association to which they belonged brought action for strict liability and negligence against owner of training facility that allegedly was source of outbreak of Equine Herpes Virus—Type 1 (EHV–1) that caused racehorses to be quarantined, which prevented them from racing.
Id. After Alpen House lost its motion for summary judgment, the parties likely settled, but this has not been confirmed.
Research is still underway to develop a vaccine that will protect horses against the neurological form of EHV, and until completed, more outbreaks should be expected.