Equine herpes virus
- kwoodham1
- Mar 19
- 2 min read
Updated: Oct 24
Equine herpes virus (EHV) is a DNA virus found in horses all around the world.
There are different strains of equine herpes virus (EHV) with the most common being EHV-1 and EHV-4. EHV-1 causes abortion, respiratory diseases (particularly in young horses) and neurological diseases, while EHV-4 causes respiratory disease and can cause abortion in pregnant mares.
Key messages
• Equine herpes EHV-1 is a notifiable disease.
• Abortions from equine herpes (EHV-1) infection usually occur during the last trimester of pregnancy, but can occur earlier in some cases.
• The virus is highly contagious and is spread by direct horse-to-horse contact via mucus and contact with physical objects contaminated with the virus.
• Infected mares that have aborted also shed the virus in mucus and the virus is present in the fetus, placenta, fetal membranes and fetal fluids. In Australia, EHV-1 is a notifiable disease (i.e. must be reported to your local vet or state or territory department of primary
industries or agriculture).
Horses are often exposed to EHV-1 early in their life — foals can be infected from one week of age from their mother. Most infected horses show no symptoms. In horses that do show symptoms, clinical signs include fever — this may be the only symptom and if temperature is not checked, can go unnoticed — coughing, nasal discharge and abortions.
Abortions from EHV-1 infection usually occur during the last trimester of pregnancy but can occur earlier in some cases.
Mares are often asymptomatic, but some will experience spikes in body temperature before aborting. Affected foals born alive usually die within a few days.
The incubation period for infection ranges from 24 hours to six days. EHV abortions can occur from two weeks to several months post infection, with the virus persisting in the horse long term. Reactivation and shedding of the virus can occur during periods of stress.
Rapid diagnostic testing
Traditional disease diagnosis is based on clinical history, histopathology and virology. Fresh tissues (placenta, foetal lung, liver, spleen and thymus), aborted foetus — whole foetus if possible — and paired blood samples from the mare are tested to diagnose infection.
Research funded by the AgriFutures Thoroughbred Horse Program has supported the development of a rapid diagnostic test, based on loop mediated isothermal amplification (LAMP), which can be performed in the clinic to diagnose EHV. The LAMP diagnostic test is currently being validated by the research team. The availability of rapid, sensitive and specific diagnostic tests, along with vaccination, will allow more timely management of EHV in pregnant mares and prevent abortion storms of several late gestation mares.
Learn more www.agrifutures.com.au/thoroughbred-horses
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