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Equine Herpes Virus infection in horses and ponies

EHV exists in several forms and EHV-1 and EHV-4, sometimes called "The Cough" or "The Virus", are known to be involved in causing respiratory problems and are also believed to be immunosuppressive - they not only cause disease but may also lower the horse's ability to fight off other infections.


Clinical signs of EHV infection can include:

  • High temperature - commonly above 39.4C (103F) and sometimes as high as 41C (106F).
  • Watery nasal discharge which becomes muco-purulent.
  • Ocular discharge in some cases.
  • Sub-mandibular lymph nodes becoming firm and enlarged.
  • Coughing -usually less harsh than with equine 'flu.
  • Loss of appetite.
  • Depression and lethargy - with horses standing dejected, head down.
  • Broncho-pneumonia due to secondary infections.
  • Viral pneumonia - particularly in young foals.
  • Abortion storms (EHV-1) and sporadic abortions (EHV-4) in some instances.
  • Paralysis, ataxia, recumbency - all linked with EHV-1.

Consequences of infection

The consequences of EHV are wide ranging and serious, including:

  • Repeated infections - natural immunity is short lived and typically no more than 2-3 months.
  • Sub-clinical disease - particularly common in older horses.
  • Carriers - with recurrence of latent virus when horses are stressed - and, therefore, further spread in infection.
  • Long-term, non-specific immunosupression - reducing horses' ability to respond to other infectious agents and vaccines.


Laboratory investigation is necessary to establish the real cause of each episode of respiratory infection and naso-pharyngeal swabs and hepranised blood can be collected for virus isolation during the first few days of infection and submitted to a suitable diagnostic laboratory.

Clotted blood samples for serology, taken in both the acute and convalescent phase (10-21 days apart) will also be helpful in detecting.

Recent EHV activity. A diagnosis may still be possible on a single convalescent sample in some cases, where the acute clinical signs may have been absent. Current serological tests, such as Complement Fixation (CF) do not reliably distinguish between EHV-1 and EHV-4 viruses and therefore virus isolation is essential for typing the virus involved.

If abortion has occurred, the only reliable method of diagnosis is to submit the entire foetus and placenta for pathological investigation and virus isolation.


The vaccine Duvaxyn EHV 1,4, has been developed to help limit the spread and intensity of EHV infections. Two vaccinations are required to establish protection for six months and each alternative booster can be timed to fit in with 'flu' injections. As a special offer, when five or more horses are to be vaccinated in one place, no call out fee will be charged.

Animed Veterinary Group is part of CVS (UK) Limited, a company which owns over 300 veterinary practices in the UK. Company Registration Number 03777473. Registered Office CVS House, Owen Road, Diss, Norfolk, IP22 4ER