Horses euthanized as Southern California equine herpes outbreak grows, officials say
California officials are warning of a deadly equine herpes virus outbreak in San Bernardino County this month.
A 13-year-old mare with a fever and neurological symptoms tested positive for the highly contagious virus and was euthanized on Oct. 29, the California Department of Food and Agriculture said in an equine health alert on Nov. 6.
Now a second horse, a 22-year-old gelding, has tested positive for equine herpes virus myeloencephalopathy and “was euthanized due to the severity of clinical signs,” officials said in a Nov. 14 update. State officials added that three other horses with fevers on the same premises also were confirmed to have the virus.
The equine herpes virus, or EHV-1, “can cause respiratory disease, abortion in mares, neonatal foal death and neurological disease,” state officials said, explaining that “the neurological form of the disease is known as equine herpes myeloencephalopathy (EHM) and may be caused by damage to blood vessels of the brain and spinal cord associated with EHV-1 infection.”
The virus spreads easily and has a two- to 10-day incubation period, state officials said. Humans won’t come down with the virus but can spread it.
Twenty horses exposed to the first horse that was euthanized were quarantined “with enhanced biosecurity measures including twice daily temperature monitoring,” according to state officials.
“Any horse displaying clinical signs or a temperature over 101.5F shall be reported to the veterinarian for evaluation and potential nasal swab and blood sampling,” officials said.
“The positive horse has no epidemiological links to any other EHV-1 cases in California and there has been no recent movement off of the property,” officials said of the first horse euthanized.
According to the U.S. Department of Agriculture, the virus is found worldwide, but the strains “EHV-1, EHV-3 and EHV-4 pose the highest disease risk in the U.S. horse population.”
USDA said that “in recent years there has been an increase in the number of EHV-1 neurologic cases, also referred to as equine herpes myeloencephalopathy.”
Horses are treated with IV fluids and anti-inflammatories to tackle their fevers, and “the majority of horses with uncomplicated infections recover,” per USDA.
According to a state equine herpes myeloencephalopathy fact sheet from April 2019, only one horse died or was euthanized due to the disease last year, while two horses were euthanized with the virus each year from 2015 to 2017.
“Since the size of the virus limits the capacity for airborne transmission to distances of less than 30 feet, direct and indirect contact are the most important routes of transmission,” officials wrote in the fact sheet. “Horses infected with EHV-1 and horses incubating the virus shed it via nasal secretions. Horses with severe clinical signs consistent with the neurologic form most often shed large viral loads in nasal secretions and present the greatest risk for disease spread.”
This story was originally published November 18, 2019 at 3:59 PM with the headline "Horses euthanized as Southern California equine herpes outbreak grows, officials say."
