Equine Virology

Virology is the study of viruses and virus-like agents. Studied is their structure, evolution and classification, diseases caused by them and techniques to isolate and culture them. In equine virology, blood samples mostly go to many different labs within the same unit, like serology (study of blood serum), haematology (study of blood components) and biochemistry (study of chemical processes). At this time of year, blood samples from horses are mainly being tested for Equine Infectious Arteritis and Equine Herpes Viruses One and Four. This is in preparation for the forthcoming important breeding season.

Equine viral arteritis (EVA) is caused by the equine arteritis virus (EAV). It is tested for using the blood serum. It occurs worldwide in both thoroughbred and non thoroughbred populations. In Ireland, EVA is a notifiable disease. The clinical signs of the virus can vary widely, from the infection being obvious to there being no signs at all. Main signs of EVA are fever, lethargy, depression and swelling around the lower legs. Since clinical signs aren’t always present, a clinical diagnosis may not always be possible, therefore laboratory diagnosis is essential. The virus is spread through mating, and can cause abortion. There is no current treatment for EVA, but treatment to alleviate some of the symptoms can be administered, and horses can be vaccinated

Equine herpes virus (EHV) occurs worldwide, and the most common strains are EHV-1 and EHV-4. Like EVA, EHV is also tested for using the blood serum. Although it isn’t a notifiable disease, owners are advised to inform the relevant breeders’ association if the infection occurs. EHV-1 can cause abortion, respiratory disease and paralysis, whereas EHV-4 usually only causes respiratory disease but can cause the occasional abortion. Abortions caused by EHV usually occur in late pregnancy (from eight months onwards). Respiratory disease caused by EHV is most commonly found in weaned foals and yearlings. The clinical signs of respiratory disease include mild fever, coughing and nasal discharge. Live foals that were infected in the womb are usually abnormal from birth, showing jaundice, weakness, and difficulty in breathing. Unfortunately, there are usually no warning signs for abortion caused by EHV. It is most commonly spread via the respiratory route. A vaccination is available for horses against EHV 1 and 4, and is strongly recommended as a general practice. Necessary treatment of an infected horse is invariably determined by the attending vet.

This article is contributed by Junior Frog Blog Reporter Emma Moore. Emma recently spent two highly successful weeks on lab experience in the Irish Equine Centre, helping to conduct equine virology tests, and has a keen interest in horses and equine science. She hopes to study Veterinary Medicine in the years to come.


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