EHV NA ISSUE 21_Jerkins feature.qxd 20/07/2011 12:28 Page 2
EHV
Scoping a horse
show neurological signs varying from mild incoordination to an inability to stand. Specific neuropathogenic strains that are likely to lead to the paralytic form of the disease have been identified. While EHV-1 infection has been associated with occasional abortions, it is most frequently a cause of respiratory disease. This article will confine itself solely to a discussion of respiratory disease due to infections with
EHV-1 and EHV-4, since this is by far the most common of the disorders associated with this group of viruses. The incubation period* for EHV varies from 1-10 days. Infections are often quite short-lived and virus is usually cleared from the respiratory tract within three weeks in horses infected for the first time and a shorter period for subsequent infections. Shedding of virus into the environment can
continue for as long as fifteen or more days after a first infection, but for as little as just two days in previously infected horses. Spread of the respiratory form of EHV infection usually occurs via aerosol transmission, nose to nose contact, and fomites*. Under suitable conditions, the virus can last for several weeks in the environment after shedding by the horse. The signs of respiratory disease due to EHV-1 or EHV-4 are very variable in severity. The most severe signs are seen in young horses. A nasal discharge is the most commonly occurring sign and there may also be fever (which is often very shortlived), lethargy, lack of appetite, mild swelling of the lymph nodes under the jaw, ocular discharge, and mild swelling of the lower limbs. EHV infections involve mainly the upper respiratory tract and since in horses coughing is associated mainly with lower airway disease, it is not usually a major sign (this contrasts with equine influenza in which lower airway involvement is a prominent feature of the disease and coughing is a frequently symptom). Older horses that have had previous exposure to the virus usually display milder signs and infection in these animals may be sub-clinical other than having an effect on exercise performance. In still other cases, there may even be little or no effect on
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