Whatever your circumstances as a horse owner or carer, if you look after one horse or a busy competition yard, the threat of infectious diseases will never be far from your mind. Hearing the words “Equine Herpes virus” can be particularly worrying, especially when high profile cases hit the headlines. This article aims to give an overview of the disease and steps that you can take to try to reduce the risk in your horses.
About Equine Herpes virus
Equine Herpesvirus, usually one of the two most common strains (of nine), EHV1 and EHV4. The infection is endemic in horse populations across the globe. Although many horses will be exposed at an early age, not all will go on to develop clinical symptoms, but these horses may have a dormant or latent form of the disease where the virus hides in nerves or lymph tissue. Stress or other illnesses may cause the virus to become active again. This latent form is one of the main reasons why it is very difficult to eradicate this disease.
Symptoms, diagnosis and transmission
The symptoms tend to vary from very mild to severe. EHV1 tends to cause respiratory disease, similar to the flu, but sometimes also abortions and neurological disease, which can lead to paralysis and death. EHV4 usually causes respiratory illness and only rarely abortion. The respiratory form of the disease is usually characterised by fever, nasal discharge, cough and lethargy. It is usually diagnosed using samples collected by nasopharyngeal swabs or paired blood samples.
In cases of pregnant mares, abortion is the main concern, and the mare can appear healthy in the period leading up to abortion. If abortion occurs, your vet will need to send the foetus to a specialised laboratory to definitively diagnose EHV1.
Another, very dangerous form exists, a neurological form, known as equine herpesvirus myeloencephalopathy. The neurological signs can occur after a respiratory infection or in the absence of any other symptoms. The clinical signs include weakness, incoordination, hindlimb weakness, urinary incontinence and in very severe cases paralysis and recumbency. It was this form of the disease that dominated the headlines during the 2021 Sunshine tour showjumping competition in Spain, when 18 horses lost their lives due to the virus.
The virus is primarily spread in respiratory secretions or by contact with aborted foetus and placenta. It is worth bearing in mind that horses in the same airspace may spread the virus up to 5m and do not have to be in direct contact. It can also be spread on tack or equipment shared between horses.
As mentioned above, your vet will attempt to make a diagnosis if they suspect your horse is suffering from EHV. Even if your horse only has mild respiratory signs, it is still very helpful to get a diagnosis as your horse will need to be isolated to reduce the risk of the virus shedding. During an outbreak, we would encourage twice daily temperature monitoring as this is often the earliest indication that the horse is suffering from the disease.
Treatment
Treatment mainly focuses on supportive care of the horse. We will usually recommend rest, anti-inflammatory medications, soft, palatable food and careful monitoring. If neurological disease develops, intensive nursing care may be needed, particularly if the horse becomes recumbent.
Vaccination can be extremely helpful in reducing the severity of the clinical signs and viral shedding, so your horse will be less sick and less likely to infect others. However, it must be said that vaccination does not reliably prevent the neurological from of the disease and abortions can still occur, although widespread abortion amongst herds of vaccinated horses is much less likely. Vaccination schedules depend on your horse’s circumstances, with 6 monthly boosters recommended for those competing. Pregnant mares are generally vaccinated at 5, 7 and 9 months of pregnancy.
In the respiratory form of the disease, most horses will recover fully. With the neurological form, mildly affected horses may recover well, however, if recumbency occurs, the prognosis is quite poor.
Prevention
It is very important to reduce your horse’s chance of exposure to the virus. Any new arrivals to the yard should be quarantined away from established horses for at least two weeks. During this time, they should be checked carefully for clinical signs such as a cough or increased lymph nodes and have their temperatures taken twice daily. It is always advisable to keep any equipment separate or cleaned between horses and remember if you go to a show, try to take your own source of water and equipment.
Vaccination will help to reduce the risk of spread of the disease and the severity of clinical signs, so it is important to ensure your horse is up to date if they are at risk. Youngsters are the most susceptible although any horse that is in contact with others could possibly be affected.
We must remember that although the virus is endemic in the population, large scale outbreaks are not common. However, we cannot be complacent. If you are worried about your horse, particularly if they develop any clinical signs, please contact the clinical as soon as possible. Our vets will be able to discuss your case with you and offer any help necessary.
