On Jan. 18, the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) received notice of two cases of equine herpesvirus-1 (EHV-1) abortion at a farm in Haldimand County, Ontario, Canada, the agency said in a statement.
“The two mares aborted during their ninth and 10th months of pregnancy,” OMAFRA said. “One week prior to the abortions, two horses on the same farm suddenly developed neurological signs consistent with the neurological form of EHV-1 infection, also known as equine herpes myeloencephalopathy (EHM). These horses were euthanized and no further diagnostic testing was performed. The farm owner has voluntarily placed the premises under quarantine to reduce the risk of disease transmission.”
The agency said current EHV-1 vaccines that protect against abortion should be administered during the fifth, seventh, and ninth months of pregnancy and according to the manufacturer’s guidelines.
“EHV-1 vaccines marketed for prevention of respiratory disease may reduce viral shedding but are not protective against developing the neurological form of the disease in the vaccinated animal,” OMAFRA cautioned.
In Ontario, EHV-1 infection is immediately notifiable by laboratories to OMAFRA under the Animal Health Act, the agency said. Attending veterinarians concerned about cases of EHV-1 infection can contact an OMAFRA veterinarian through the Agricultural Information Contact Centre at 877/424-1300, it said.
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 the neurologic form 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 present disease spread.