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African Horse Sickness (AHS)

African Horse Sickness (AHS) is highly infectious viral disease which frequently proves fatal. There have never been any cases of African Horse Sickness in the UK and, for many years, it was barely been considered a threat to British horses.

However, with climate change and an increase in the international movement of horses there is a possibility that AHS could reach Britain, although the risk is not presently considered to be high. However, were AHS to arrive on these shores it is imperative that it is spotted quickly in order that it can be dealt with rapidly and prevented from spreading. Your vet can advise on what to look out for.

AHS is a notifiable disease. This means that if you suspect a horse may have it, you must immediately notify the duty vet in your local Animal Health Veterinary Laboratories Agency (AHVLA) office.

How is AHS spread?

The AHSV is carried and transmitted by particular species of midges from the Culicoides family. AHS is transmitted to a horse by the bite of an infected female midge.

Can horses catch AHS directly from each other?

No, the disease is not directly contagious between horses, even when they are kept in close contact. However, when horses are in close proximity, the likelihood of a midge biting an infected horse and then going on to bite and infect a healthy animal is obviously increased. AHS is not directly contagious to any other species of animal.

Types of AHS

There are three main different forms of AHS; the lung form (acute form), the heart form (cardiac) and the mixed form (combination of lung and heart form).

What are the clinical signs of AHS?


  • High, rapid rise in temperature (up to 41°C)
  • Severe difficulty in breathing with mouth open, head hanging and the nostrils dilated
  • Respiration rate may exceed 50 breaths per minute
  • Excess sweating
  • Presence of abdominal heave lines due to forced expiration
  • Large amounts of frothy discharge from the nostrils
  • Redness of conjunctivae
  • Coughing
  • Within a week 90 percent of horses will die. Once the horse is showing signs of respiratory distress, death usually occurs within 30 minutes to a few hours


  • Fever (39-41°C)
  • Swelling of eyelids, facial tissues, neck and shoulders
  • In severe cases the entire head swells
  • Loss of ability to swallow
  • Respiratory distress shown due to the increased swelling
  • Colic symptoms potentially leading to severe colic
  • Terminal signs include bleeding in the membranes of the mouth and eyes
  • Once the horse shows signs of fever, death usually occurs four-eight days later
  • Lower death rate (50 percent)


  • Symptoms of both the acute and cardiac form – initially mild respiratory signs are exhibited followed by the typical swellings of the cardiac form
  • The mortality rate is 70 percent

Download our guide to African Horse Sickness


If you suspect your horse has AHS contact your veterinary surgeon immediately.

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