The Equine Disease Communication Center said the affected 15-year-old Quarter Horse mare, which had been vaccinated, began showing neurologic signs, including hind-end weakness, on April 3 and was confirmed positive for EMH on April 4. The WLSB said the mare is quarantined at her home facility in Johnson County along with 19 other horses.
It is currently unknown where the horse contracted the disease, but she attended college rodeo events March 15-16, at the Camplex in Gillette, Wyoming, and March 21-24 at the Goshen County Fairgrounds, in Torrington, Wyoming.
Thach Winslow, DVM, Wyoming assistant state veterinarian for field operations, said any horses that were at these events should be considered potentially exposed, and owners should take preventive measures, including monitoring the animals closely and checking their temperatures at least twice daily. If any horses show neurologic signs or fever, owners should isolate them and contact their veterinarians for advice and treatment options.
The WSLB noted that, in the last 30 days, EHV-1/EMH cases have been reported in several states—including Arizona, California, Idaho, and Nevada—following competitions and other equine events. Owners who plan on taking their horses to equestrian facilities and events can help prevent spread of the disease by practicing proper biosecurity measures. This includes not sharing equipment such as water/feed buckets and tack. They should also isolate their horses if they suspect them of being sick, and not allow them to leave the premise until cleared by a veterinarian.
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.
Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.