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Equine infectious anaemia (Swamp fever)

Equine Infectious Anaemia (EIA) is an exotic viral disease that affects horses, mules and donkeys. It is spread via biting insects.

The disease is notifiable: if you suspect the disease, you must immediately notify the duty vet in your local Animal Health Veterinary Laboratories Agency (AHVLA) office.

Horses are most likely to become infected when travelling abroad to areas or countries where the disease is endemic, or from the use of biological products infected with the EIA virus. The disease is often fatal to horses. In England infected animals are humanely destroyed to control its spread.

Latest situation

1 February 2013 – An incident relating to the confirmation of Equine Infectious Anaemia in two horses in Devon and Cornwall in October 2012 is now closed. The two affected horses were humanely culled, and all at risk horses under restriction have been re-sampled and tested negative. All restrictions have been lifted.

About the disease

Equine Infectious Anaemia (EIA) is a viral disease that affects horses, mules and donkeys and is most commonly spread by biting insects such as horse flies. There is no treatment and horses do not recover from the disease, which can be fatal.

The Health Protection Agency has said EIA cannot be spread from animals to people and is not a risk to human health.

The disease does not spread quickly and is unlikely to spread widely from infected horses as the flies that transmit the disease only travel short distances to feed.

EIA is often fatal to horses. If the affected animal recovers it remains a lifelong carrier of the disease and will thereby be infectious to other animals, therefore all infected animals must be humanely destroyed to control the spread of disease.

International disease monitoring

The disease does not commonly occur in Great Britain but it is present in other parts of the world. Details of the latest situation can be found at international disease monitoring.

7 September 2012 - Preliminary outbreak assessment: Equine Infectious Anaemia in Western Europe (PDF)

24 June 2011 - Qualitative assessment of the risk of introduction of Equine Infectious Anaemia (EIA) into Great Britain from an EIA endemic area through temporary movement of UK origin horses (PDF 350KB)

Previous cases

30 March 2011 – Following the two cases of Equine Infections Anaemia in September 2010, Defra published the reports of the epidemiological  investigations in Northumberland (PDF) and Devon (PDF), and a lessons learned report.


The most important way that this virus is transmitted normally is through large biting flies such as horseflies (tabanid species) or stable flies (Stomoxys calcitrans).

Transmission of the disease may occur where there are adult flies of this type in proximity to infected horses. The adult flies are only active between May and September, with activity peaking in July-August. The flies overwinter as larvae and the larvae cannot transmit the disease.

In addition, the flies normally travel no more than 200m to feed and are not likely to be moved long distances by wind; therefore we would not expect infected flies to spread far from the point of an infected horse.

EIA is not spread by small flying insects such as midges and mosquitoes under normal conditions.

It is possible for disease to be transmitted by equipment that is contaminated, especially if this contamination is with blood, milk or maternal/placental fluid. Relevant equipment could include veterinary instruments e.g. needles and scalpels, dental, obstetric grooming, tattooing, farriery and tack such as bridles. However, it is important to note that good hygiene practices will reduce the risk of transmission by these routes to negligible.

It may also be spread by saliva, nasal secretions, faeces, semen, ova, and embryos. However, the risk from these routes is low and can be mitigated by good hygiene measures.

Pregnant mares may pass the disease to their foals in the womb.

How to spot the disease

Animals may be affected acutely, chronically, or sub-clinically. The incubation period is variable, from a matter of days to a few months, but is generally one to three weeks.

The disease is characterised by a recurring fever, anaemia, oedema (fluid retention), emaciation and death. However, many horses have very mild or unapparent signs on first exposure. Owners of such animals are unlikely to realise that they are infected unless serological testing is carried out. All infected horses, including those that are asymptomatic, become carriers and are infectious for life.

Although they may never recover from the acute stage of infection the chronic phase of the disease may lead to ill-thrift and impact on infected equines for the rest of their lives, predisposing them  to secondary infections and worm burdens.

Diseases that can appear similar to EIA include:

  • Notifiable diseases: African Horse Sickness, Anthrax, Dourine, Equine Viral Arteritis, Japanese Encephalitis
  • Systemic diseases: Equine Influenza, Equine Herpes Virus, Babesiosis, Ehrlichiosis, Leptospirosis, Fascioliasis, systemic infection or abscess

Affected horses

If an animal does test positive for EIA, the only course of action is to humanely put it down. This may be for the welfare of the affected horse, but also to protect other horses from infection.  We have agreed with equine industry veterinary surgeons that destruction is the only policy. Legislation was introduced in August 2006 to provide powers to slaughter horses affected with EIA. We would only invoke our powers to destroy the horse if an owner refused to co-operate. If the powers to slaughter need to be invoked, AHVLA will facilitate safe carcass removal and destruction.

We will only cull animals that have tested positive with the appropriate blood test. With this disease, we are not culling animals on suspicion. In addition, each animal that has been traced as a contact with infected animals will be kept under restrictions and tested until we are satisfied that it is not affected by the disease. Restrictions will be lifted when a veterinary risk assessment advises that the risk is low.

Disease prevention

If an EIA outbreak were to occur in the UK, preventing your horse being bitten by horseflies, and practising good basic biosecurity, would currently be the best protection available. No vaccine is available for routine use.

Preventing your horse from being bitten by horse flies is difficult and there is no mechanism of protection that will guarantee your horse will not be bitten at all. The information below outlines protective measures that can be taken to decrease the risk of attack by these flies.

Decreasing the risk of attack

No veterinary medicines are currently authorised to act specifically against horseflies, but there are products licensed for use on horses as insecticides and as insect repellents.  It is important that you seek advice from your Vet and read the instructions for these products carefully and use them as directed.

Legislation covering slaughter of equines affected by EIA

On 6 November 2006 the Equine Infectious Anaemia (Compensation) (England) Order 2006 came into force.

On 29 August 2006 the Specified Diseases (Notification and Slaughter) Order 2006 came into force and amends the Specified Diseases (Notification and Slaughter) Order 1992 by adding EIA to the list of diseases under the Animal Health Act 1981 which may be slaughtered.

Government action to reduce the risk of EIA entering the UK

On 3 May 2007, Council Decision 2007/269/EC (PDF KB) on protective measure with regard to equine infectious anaemia in Romania came into force.  It requires equidae, or ova and embryos of equidae originating from Romania to be subject to a Coggins test prior to export.

On 14 September 2006, Defra published a qualitative risk assessment on equine infectious anaemia which was copied to the EU Commission for consideration.

Under the scope of the Tripartite Agreement Defra keeps regular communications with the Irish Agricultural Department to monitor closely the EIA situation in Ireland. Following the EIA outbreak in Ireland in 2006, any horse moved from Ireland into the UK, which may have presented a high risk, was traced back to the premises of destination and put under restriction until negative tests eliminated the risk.

On 26 June 1990 the animal health conditions governing the intra-Community trade and import from third countries of equidae were harmonised through the whole of the EU by the implementation of Directive 90/426/EEC. There is limited scope for the UK Government to adopt unilateral measures in relation to EIA.

On 20 May 1987 the Infectious Diseases of Horses Order, which revoked and replaced earlier legislation, made EIA compulsorily notifiable.  It gave an inspector powers to declare an infected place where disease is suspected; to carry out a veterinary inquiry, prohibit the movement of horses carcasses and other things onto or off the premises and requires cleansing and disinfection.


Page last modified: 1 February 2013