Equine Infectious Anaemia
Equine Infectious Anaemia (EIA) or "swamp fever” is a virus disease of horses, mules and donkeys causing intermittent fever, anaemia, emaciation and death. The disease does not affect people and there is no impact on human health.
If notifiable disease is suspected, contact the DAERA Helpline on 0300 200 7840 or your local DAERA Direct Regional Office. Failure to do so is an offence
What is Equine Infectious Anaemia (swamp fever)?
Although it is not necessarily fatal, recovered animals become carriers of the disease and can infect other horses. It can be transmitted by mechanical transfer of blood by biting insects and occurs typically in low-lying swampy areas. The disease was first described in France in 1843. The term "swamp fever" was first used by Torrance in 1903 in Canada, where this disease had been known before 1882.
The disease is found worldwide. In Europe, EIA has been reported in Belgium, Bulgaria, France, Netherlands and appears to be endemic in Romania.
Clinical signs
Equine Infectious Anaemia (EIA) is a viral disease of horses transmitted by an insect vector, in this case by the mechanical transfer of infected blood from animal to animal by biting flies, usually involving clegs/horse flies (Tabanids).
The virus can also be spread by contaminated blood products and contaminated equipment. Transplacental spread also occurs.
Disease may be acute, chronic or subclinical in horses infected with the same strain of the virus. The incubation period is usually 1-3 weeks but can range from a few days to a few months. Antibodies usually, but not always, develop 7 to 14 days after infection and last for life. Horses have been known to take several months before clinical signs or antibodies are apparent.
In acute disease clinical signs include: pyrexia, depression, ataxia, rapid weight loss and occasionally haemorrhage. Disease may be fatal within days with no sign of anaemia.
In chronic cases recurring cycles of anaemia, oedema, weight loss and lethargy are seen. An enlarge spleen may be detected on rectal examination. Mares may abort. Persistent replication of virus within the host leads to the periodical emergence of new strains which vary antigenically and are frequently resistant to the neutralising antibodies circulating in the horse causing a recrudescence of clinical signs which usually decrease in severity over time.
Subclinical disease resulting in seropositive asymptomatic carriers.
The differential diagnosis includes other febrile illnesses including equine viral arteritis, purpura hemorrhagica, leptospirosis, babesiosis, severe strongyliosis.
How is the disease transmitted?
The virus is usually transmitted mechanically, most commonly through blood-sucking insects (Tababus or Stomoxys species) or through the use of contaminated blood or blood products, instruments or needles. Transmission of the disease may occur where there are large numbers of horseflies in proximity to acutely affected horses and occurs most often during periods of high insect activity, in low-lying swampy areas close to woodlands.
Contaminated needles and blood products have also been implicated in the infection of horses, and transmission via colostrums or semen is uncommon. Pregnant mares may pass the disease to their foals in the womb.
Prevention
You can help prevent Equine Infectious Anaemia by practising good biosecurity on your premises.
How widespread is this disease?
Although the infectious nature of this disease had long been suspected, a viral case was not definitely established until 1904. The virus was classified as a retrovirus in 1976 and later grouped with the lentiviruses (that is, non-tumour forming exogenous retroviruses) of which the human AIDS virus is also a member.
EIA has a worldwide distribution. Early in the twentieth century serous outbreaks occurred in France, Japan and America. The disease has been reported in many parts of America, Asia (India, Malaysia, Myanmar, Philippines, Thailand), Europe (Austria, France, Greece, Italy, Romania, USSR, Yugoslavia) and Australia. The last case in Northern Ireland was in 2006.
Are restrictions placed on suspected, infected or horses exposed to infection?
Yes, suspect horses are tested and placed in quarantine for a minimum of 60 days post exposure. This quarantine requires the separation of suspect horses from other horses, use of vector control methods such as fly repellents, and insect proof barriers. Should this initial test prove negative, further testing is carried out over the course of this quarantine period. If further tests prove negative restrictions are removed. If further testing proves positive, the affected animal would be euthanised and further testing of at risk horses carried out to detect any disease spread.
There is currently no effective treatment for EIA and no vaccine available.
What are the EIA health requirements for moving horses between Member States of the European Union?
In order to move horses between EU Member States, strict health requirements regarding Equine Infectious Anaemia (EIA) must be met.
Firstly, there must be no cases of EIA on the premises for at least 90 days prior to export.
In addition, there must either have been
No case of EIA on the establishment in the previous 12 months OR
If outbreak occurred, premises remain under movement restriction until either,
- 2 negative samples from remaining equines, 90 days apart, first sample taken after removal of last infected animal, plus C&D OR
30 days after date of cull of last equine plus C&D i.e. all animals on premises were culled