Equine infectious anaemia

Equine infectious anaemia (EIA)  is a viral disease. The virus wich causes it belongs to the Retroviridae family (the same family as the AIDS virus).

All species of equids are prone to EIA (horse, mule, donkey…). The virus only spreads to equids and is not transmissible to Man.

EIA is not stictly speaking a contagious disease : it is a blood-borne infection, via biting insects, (more particularly horse flies) or via contaminated equipment (e.g using a same contaminated needle to obtain test samples from several horses).

An infected horse remains a lifelong carrier of the virus in the blood, and can therefore contribute to infecting other horses. It should be noted however that the circulation of the virus in the blood is intermittant. Natural direct transmission of the disease from one equid to another is rare.

The incubation period^[1] ranges from a few days to a few weeks (the average being 10-15 days). 
There are different clinical forms of the disease :

Superacute form

This form is rare and especially affects younger equids. The animal develops a very high temperature (T>40°C), intense depondancy and death within 1 to 3 days.

Acute form

To begin with the sypmptoms are a temperature, anorexia, local ocular symptoms (weeping, yellowish conjunctival mucouses on a red background). Then, the disease worsens and oedema appear on the lower areas (the limbs for example). Death usually occurs within 10 days in 80 % of the cases. For the other 20 %, the disease will then evolve towards a chronic or latent form.

Subacute form

The symptoms are lessened and more spaced out over time, with « bouts » (reappearance of the symptoms) interspersed with remission periods. The main clinical signs are a high temperature and oedema of the lower areas of the body, and marked anaemia.

The bouts can be triggered by stress (after intense work, a race, etc., heat, gestation, or administration of other treatments).

The evolution of this form can take time, and death may occur during an acute bout, or the disease progresses to the chronic form.

Chronic form

This form follows the acute or subacute forms or can occur as from the onset. The evolution takes a long time, sometimes over several years, with non-specific symptoms : loss of weight, loss of performance, slight temperature, high increase of the heart rate at effort, slightly yellow mucous linings (« puffy eyes »), more or less severe anaemia.

Acute bouts can occur. Death occurs after several months or several years.

Latent form

After one or several bouts the animal seems to be cured, but he continues to host the virus and can transmit it.

Asymptomatic form

There are also animals who are carriers of the virus, apparently in good health, with no apparent symptoms : they are the healthy carriers.

This asymptomatic form is the most common in France in horses.  Donkeys are for the main part healthy carriers .

____________________

[1] Incubation period:lapse of time between contamination and the appearance of the first symptoms of a disease.

There is no existing treatment.

As there is no vaccine against EIA, the most effective means of preventing its spread is to have horses tested on a regular basis so as to detect those infected by the virus. Positive results lead to immediate isolation of the infected animal from other equids.

Measures to fight against insects are limited in efficiency, but are nevertheless an additional preventive measure : fly masks, fly traps for horse flies. Insecticidal treatments can be used, but their efficiency and especially their persistance are low. When using them, it is imperative to respect the instructions for use provided on the products.

Another major preventive measure concerns contaminations via equipment : any injection should be carried out with one time equipment (new needle and syringe for each animal) for any blood transfusion the donor animal must be tested.

Equine infectious anaemia is subject to state regulations and ranked as a category 1^[2]sanitary hazard  (article L.201-1  of the rural code , Arrêté ministériel du 29/7/2013). Testing for EIA is compulsary in the following cases :

• For stallions used in artificial insemination and for stallions of certain breeds used in natural servicing of mares ;
• For export to other countries and for intra-community exchanges of semen ;
• For the import of equids from other countries ;
• For the export of equids to other countries.

Testing should also be requested when buying a horse, even more so as AIE is a crippling vice, with an invalidation period of 30 days.

 When a test is positive, a declaration is made by the testing laboratory, or by the sanitary veterinarian to the DD(cs)PP^[3] in the area where the horse is kept. Sanitary policing measures are then implemented on the yard or stud concerned (census and testing of the equids present, movement restrictions, etc), and an epidemiological investigation is carried out over a defined geographical area around the cluster, so as to determine whether any equids having been in contact with the infected animal could also be infected.

When positive cases are confirmed in France, the state should then inform the Office International des épizooties (OIE) (World organisation for animal health), so as to promote transparency in international exchanges of equids and their semen.

Sanitary policing measures are established by the Ministerial Decree dated 23^rd September 1992.
 

____________________
[2] Category 1 sanitary hazards :according to the Rural Code « sanitary hazards potentially endagering public health, or seriously impeding national production capcities or environmental salubrity. These hazards require State measures for prevention, surveillance, defined and imposed control, in the general interest.  [3] DD(cs)PP : Departmental Direction in charge of (social cohesion and ) the Protection of Populations.  

Equine infectious anaemia (EIA) is geographically out the world. In Europe, it is largely present in several countries, particularly in Roumania and Italy. EIA clusters are regularly declared in the south of France.

* : Number of yards or studs where at least one case was detected.
** : Number of horses declared infected.