Two confirmed cases of abortion due to equine herpesvirus-1 in Haldimand
On January 18, 2019 the Ontario Ministry of Agriculture, Food and
Rural Affairs (OMAFRA) was notified of two cases of equine herpes
viral abortion caused by equine herpesvirus-1 (EHV-1) at a farm
in Haldimand County. The two mares aborted during their 9th and
10th month of pregnancy. 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.
In Ontario, EHV-1 infection is immediately notifiable by laboratories
to OMAFRA under the Animal Health Act. Attending veterinarians concerned
about cases of EHV-1 infection may contact an OMAFRA veterinarian
through the Agricultural Information Contact Centre at 1-877-424-1300.
EHV-1 infection in horses can cause
respiratory disease, abortion,
neonatal foal death, and/or neurological
Because a fever (101.5 °F or 38.6 °C) may be the first
indication of infection, the body temperature of exposed animals
should be monitored twice daily for 21 days and any abnormalities
discussed with a veterinarian. Neurological signs, if they develop,
may include loss of balance, hind-limb weakness, difficulty urinating,
decreased tail tone, depression and being down and unable to rise.
It is important that a veterinarian assess horses demonstrating
neurological signs since it can be difficult to distinguish EHV-1
from other serious diseases such as rabies.
Broodmares that abort due to EHV-1 infection
may not show any clinical signs
but will shed large amounts of
virus in aborted fluid and tissue.
EHV-1 infection is easily spread to other horses by nose-to-nose
or close contact with an infected horse or aborted fluids, by sharing
contaminated equipment including bits, buckets and towels or by
the clothing and hands of people who have recently had contact with
an infected horse.
Prevention is the best medicine
Biosecurity is key to preventing spread of EHV-1. Strict routine
biosecurity measures are the best way to minimize viral spread and
should be in place at all times to prevent a disease outbreak, including
hand hygiene and basic cleaning and disinfection practices.
Pregnant broodmares should be housed separately from other groups
of horses such as young stock, boarders and horses in training.
Stress increases the risk of horses shedding the EHV-1 virus, even
years after initial infection. Stress caused by severe weather should
be minimized by access to appropriate shelter, food and water. And
stress due to transport and mixing of social groups should be avoided
when possible in the last trimester of pregnancy.
Current EHV-1 vaccines that protect against abortion should be
administered during the 5th, 7th and 9th months of pregnancy and
according to the manufacturer's guidelines to limit the amount and
time that the virus is shed. 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
For additional information
Alberta Veterinary Medical Association and Alberta Equestrian