Outbreak of Equine Herpes Virus Abortion in Australia

At the start of the last breeding season in Australia a number of studs in Victoria and NSW experienced abortion caused by equine herpes virus in their mares. Although similar outbreaks had occurred in 1989, 1994 and 2000, according to Professor Michael Studdert, virologist at the University of Melbourne, this outbreak was the worst seen in Australia. The virus causing the outbreak is believed to have been introduced from a mare or mares recently imported from America to Victoria. Attempts to minimize its spread were made by quarantining properties on which it occurred and restricting the movement of mares.

Equine Herpes virus abortions have been known to occur in New Zealand from time to time but for some unknown reason they seldom affect large of numbers of mares on studs as is experienced in Australia. This is surprising since we have evidence that more than half of the Thoroughbred population has been exposed to the virus.

Once the mare has contracted the virus it is thought to remain in its body for life in much the same way as some herpes viruses do in humans. It appears that it is activated by some means (thought to be stress) in late pregnancy in some mares which then abort or give birth to seriously ill foals most of which die within a few days. To minimize the spread of this disease it is important that affected mares are identified. For this reason all late term abortions and foals which die shortly after birth should be examined by a veterinarian and samples sent to a laboratory to determine whether or not equine herpes virus was the cause. While waiting for the results the mare should be kept in isolation.