skip to content

Equine Infectious Anaemia

Equine Infectious Anaemia (EIA) is also known as Swamp Fever and is caused by the equine infectious anaemia virus. The virus occurs worldwide, including in parts of mainland Europe and in all horse populations. It is a notifiable disease in the UK which means that a vet must notify Government if this disease is found. There are two forms of this condition. The acute form can show outward signs of fever (raised temperature), depression, increased heart and respiratory rate, haemorrhaging, bloody diarrhoea, loss of co-ordination, poor performance, ataxia, rapid weight loss, skin swelling and jaundice. The chronic form of EIA may be characterised by recurring bouts of fever (raised temperature), depression, anaemia, weakness or weight loss, interspersed with periods of normality. Sub-clinically infected horses may not show any clinical signs of disease.

How is it spread?

The virus is transmitted between horses by transfer of infected blood or blood products. This can occur in the following ways...

  • By insect vectors such as biting flies (including horse, deer and stable flies) and (very rarely) mosquitoes
  • By administration of infected blood products and unauthorised blood-based veterinary medicinal products
  • By contaminated veterinary or dental equipment or other equipment that may become contaminated by blood and act as a vector between animals, e.g. rasps, twitches and curry combs
  • From mare to foal via the placenta, or, rarely, via virus-contaminated colostrum or milk in newborn foals
  • Transmission through semen is uncommon but cannot be written off

Both clinically and sub-clinically affected horses can be a source of infection for other horses, although animals suffering acute disease or recurring bouts of chronic disease are likely to be the most highly infectious.


There is no vaccine available for EIA. Prevention of EIA is therefore based on the establishment of freedom from infection by blood ('serological') testing.

What do I do if I think we have EIA in our yard?

Clinical diagnosis is not always possible. Laboratory diagnosis, through blood testing, is essential. If you suspect this disease, call your vet without delay. Detectable antibodies are usually present in the blood 7-14 days after infection and remain present for the rest of the horse's life. Diagnosis should be by means of the Coggins test, which is currently the only test recognised officially for the purpose of international movement of horses.

What do I do if EIA is confirmed?

Control of EIA is by preventing transmission of infection to other horses through insect (vector) control and by avoiding procedures which may cause the transfer of blood products. If infection is suspected, or a horse has been in-contact with an infected horse...

  • Stop all movement of horses on and off the premises
  • Seek veterinary advice
  • Isolate the horse
  • Any directions given by the Animal and Plant Health Agency must be followed, including implementation of insect (vector) control
  • Treat the horse(s) as advised the attending veterinary surgeon
  • Veterinary procedures represent a particular risk. Veterinary equipment must therefore be either destroyed after use or appropriately sterilised
  •  Inform...
    • Owners of horses at, or due to arrive at, the premises
    • Owners of horses which have recently left the premises
  • Stables, equipment and vehicles used for horse transport must be cleaned and disinfected
  • Good hygiene is crucial. Use a different team to care for each group of horses if possible, or change all clothing, sterilise footwear, use hand gel and use different equipment
  • The virus can survive in blood, faeces and tissue so all such material must be removed and destroyed promptly and surfaces disinfected.

Horses that have come into contact with an infected horse or a horse which is suspected of being infected must be quarantined for a minimum of 90 days post-exposure. Blood testing must be repeated as directed until freedom from disease is confirmed.