Equine Rhinopneumonitis

A highly contagious disease, equine viral rhinopneumonitis is also known as viral abortion.   As is inferred from the name the disease can result in abortion following possible respiratory and neurological problems. Equine viral rhinopneumonitis is caused by a strain of the herpes virus called the equine herpes virus type 1 (EHV-1). Currently there is no evidence to suggest that equine viral rhinopneumonitis affects species other than the equine family.

Symptoms include respiratory infection and sometimes the central nervous system is adversely affected, for example leading to paralysis. Generally a high temperature, lack of appetite and nasal discharge is observed following infection. Those more susceptible to infection are foals and young horses although horses of all ages are able to catch the disease. The age of the infected horse also leads to different levels of severity concerning the signs and symptoms.

The disease is usually transmitted via infected aerosol droplets if inhaled by the horse. Due to the fact that the disease cannot be transferred to humans, the disease is not known as zoonotic. Vaccinations are available to protect against this disease though do not always provide complete protection.


The virus which causes equine viral rhinopneumonitis is transmitted via infected aerosol droplets inhaled by the horse. Contaminated surfaces such as clothing, buckets, footwear and even hands can cause the spread of the disease which means that even owners with just the one animal can put their horse at risk.  Some horses can even shed the virus without showing any symptoms which is also a cause for concern. In addition, transmission can occur following ingestion of infected faeces, nasal discharge and saliva.

The herpes virus is able to survive for as long as two months and so following infection strong disinfectants containing bleach or ammonia should be used to destroy the virus on contaminated surfaces, thus preventing further transmission. Any bedding that was present near or with the infected horse should be gotten rid of and good ventilation is required to dry out the stables.


The milder form of the disease includes a high temperature, nasal discharge, a distinct difficulty in attempts to urinate and a lack of appetite. The nasal discharge will be serous in appearance and texture. Young horses usually recover if a secondary infection such as pneumonia is not present. In some circumstances, equine viral rhinopneumonitis can progress giving rise to an attack of the central nervous system (CNS) which can result in uncoordinated gaits, the horse not being able to stand up and even paralysis.

The symptoms and clinical signs of equine viral rhinopneumonitis are more severe in younger foals where death can occur within just one day. Mares can abort their unborn foetuses during the last few months of pregnancy, usually between eight and eleven months, which can have adverse economic implications. This is caused by respiratory problems as the foetus no longer has an adequate supply of oxygen since it will have been separated too early from the placenta.

Treatment and Prevention

Only supportive treatment can be given to the infected horse as, unfortunately, there is simply no cure against equine rhinopneumonitis. The horse should stop work and antibiotics are often administered to prevent the possibility of bacteria causing what is called a secondary infection.  

Vaccinations are available against equine viral rhinopneumonitis and are initially given to horses as young as three months old and then the second dose given one month later. Following this, boosters are normally given twice yearly to provide long term immunity although for pregnant mares the schedule is a little different. They are vaccinated every two months during pregnancy, with first commencing at around the fifth month. Currently, the vaccine does not yet protect against the neurological implications which may be a result of an infection of the virus. Competing horses which travel a lot are strongly encouraged to be vaccinated.

Diagnosis and Prognosis

Following an observation of the signs and symptoms, blood samples are taken and tested for the disease. Most cases recover but in horses where paralysis and the inability to stand up is observed, the prognosis is rarely good.


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