Equine herpes virus (EHV) is a contagious viral infection which can cause respiratory disease, abortions and neurological disease.
There are two different types of EHV which mos commonly cause disease in horses:
EHV-1: In breeding mares, an infection of EHV can seriously endanger the life of her foal, causing abortions in the last third of pregnancy. EHV-1 is the most commonly diagnosed cause of infectious abortion and we strongly advise protecting breeding mares. See our information sheet - Guidelines for reducing risk of EHV-1 in pregnant mares
In rare cases an EHV-1 infection can cause a neurological disease. Infected animals can become paralysed, collapse and have a very poor prognosis for survival. This is because the virus damages the blood vessels supplying the spinal cord, causing the sinal cord to die. We don't know why some horses go wobbly and collapse 1-6 days after having a high temperature and others just have a cough.
EHV-4: This is very common and causes respiratory disease. Although overtly less serious in nature, it can cause a low grade infection - the strain on the immune system can drag your horse down for a number of weeks and cause great disruption to competition and racing yards.
EHV2+5 can cause uveitis (an often painful and sometimes blinding eye condition) - never ignore changes in the appearance of your horse's eyes.
EHV does not stimulate significant natural immunity after initial infection and the main concern for the equine population as a whole is the way the disease persists in our horses. Once a horse is infected, that individual can harbour the virus throughout its life and potentially shed the disease to other animals without showing any outward signs. Re-activation and shedding from infected horses tends to happen when they are stressed - typically when the horse moves yards or is in hard work.
Any carrier or infected horse can start shedding the virus through nasal droplets (ie. like an aerosol spray from the nose), which can then infect others in close contact. Nose to nose contact is the most common method of spread, but people and tack can spread the virus too.
In most cases of EHV infection the signs are limited to mild respiratory disease (runny nose, cough, swollen glands or legs, off food), but there may be no signs at all. A high temperature is usually one of the first signs, (be suspicious of anything above 38.5oC (101oF)
Prevention and Management
Stable management and vaccination, in particular when dealing with potentially infected horses, are key to the control of the disease. Minimising the potential stresses that set off disease spread is important as well as reducing issues such as overcrowding. Horses that are sick must be isolated. The virus can survive in bedding or on grass for a few days.
However this is not the whole answer and vaccination can play a big role. Vaccinating your horse will help prevent disease and perhaps more importantly will also help reduce the amount of infective virus that is shed to other in-contact horses, thus reducing the amount of disease present on your yard. In our experience, yards which vaccinate against herpes virus have less problems with coughs and breathing problems.
Contact the practice for more information about EHV vaccination and the risks to your horses.