Equine infectious anaemia

Equine infectious anemia virus (EIAV)

Changed on: 18.12.2020
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Equine infectious anaemia (EIA) is a viral disease of horses and other equidae, which is mainly transmitted by bloodsucking insects.

Occurrence

The EIA virus can be found worldwide. In Europe the disease is considered endemic in Romania, therefore strict rules apply to the transport of live horses from Romania.

Host animals

Host animals are odd-toed ungulates such as horse, mule, hinny, donkey, zebra etc. According to current knowledge, there is no danger of infection for humans.

Mode of transmission

Transmission occurs mainly by blood-sucking insects such as mosquitoes, flies (stable flies) and horse flies. Transmission over longer distances (more than 200 m) could not be observed. Horse-to-horse transmission via body fluids requires close animal contact.

Incubation period

1-3 weeks, rarely longer than 3 months

Symptoms

The course of the disease depends on the general condition of the animal: Fever above 40 °C, loss of condition and weight, fluctuation on the hindquarters, often edema on limbs, abdomen and under chest. The infectious equine anaemia of horses can occur as peracute (sudden death), acute or chronic manifestation. The acute form of the disease is usually fatal and the animals can die within a few days. In the case of chronic disease, the disease can last for several years.

Therapy

So far, there is no treatment for infectious equine anaemia. The EIA virus can be inactivated by commercially available disinfectants.

Prevention

Infectious equine anaemia is an animal disease which must be notified under the Animal Diseases Act. There is no effective vaccine.

Situation in Austria

In 2019, two cases of equine infectious anaemia were confirmed by AGES. These were the first cases in Austria since 2002: On June 18, 2019, a suspected case of EIA was reported in Lustenau (Vorarlberg) in a hobby farm. Examinations by the official veterinarian and by the national reference laboratory of AGES confirmed the suspicion. A second case of EIA in the district of Perg (Upper Austria) was confirmed by AGES on June 28, 2019. All horses within a radius of one kilometre around the outbreak farms were sampled and serologically tested by the local veterinary authority. 292 subsequent examinations of serum samples from the areas around the confirmed cases gave negative results.

Figure 1: EIA investigations in Austria


Legende

    Professional information

    Infectious equine anaemia (EIA) was first diagnosed in France in 1843. The causative agent of Equine Infectious Anemia virus (EIAV) is a lentivirus of the Retroviridae family, subfamily Orthroretrovirinae. EIA hosts are all odd-toed ungulates of the equine family (Equidae), i.e. horses, ponies, mules, hinnies, donkeys, zebras, etc.

    The virus is not considered to be a risk to human health, according to the current state of knowledge there is no risk of infection for humans.

    The EIA virus is spread worldwide: North, Central and South America, South Africa, Northern Australia, Japan, Great Britain, Belgium, Germany, France, Italy, Romania, Slovenia, Croatia, Hungary and Greece. The outbreaks reported in the first half of 2010 in Belgium, Germany, France and England can be attributed mainly to horses moved from Romania (SCoFCAH 2010). The disease is considered endemic in Romania and therefore strict rules apply to the transport of live horses from Romania. The EIA virus can be inactivated by commercial disinfectants. Fat solvents, strongly acidic and alkaline compounds are suitable as cleaning agents or disinfectants, but not aldehydes such as formaldehyde and glutaraldehyde.

    Mode of transmission

    Infectious equine anaemia is mainly transmitted by blood-sucking insects such as mosquitoes, flies (stable flies) and horse flies. The EIA virus only lasts for 30 minutes to several hours on the mouth parts and is not multiplied in the insect. Transmission over longer distances (more than 200 m) has not been observed so far. The transmission rate increases in late spring, culminates in late summer and early autumn and is lowest in winter. In river valleys, swamp and forest areas, the incidence of disease is highest after grazing, but lower on high pastures and in livestock housing. The regional and seasonal distribution patterns are explained by the occurrence and population density of the insects, and the transmission from horse to horse requires close contact with animals. The virus reservoir is formed by chronically or symptomlessly ill horses, which are lifelong carriers of the virus. These animals are potential sources of infection for introducing the virus into disease-free herds. Transmission can occur during the reproductive act, in pregnant mares via the placenta to the foetus, the mother's milk, and shedding via saliva and urine, as well as through blood and secretion contaminated care utensils, through the mouth fence, injection needles, surgical instruments and unlicensed blood and plasma products.

    Symptoms

    The course of the disease depends on the general condition of the animal. The incubation period is 1-3 weeks, rarely longer than 3 months.

    The infectious anaemia of horses can appear as peracute (sudden death), acute or chronic manifestation but can also be largely asymptomatic. The acute form of the disease usually ends fatal within a few days. In the case of chronic disease, the illness can last for several years.

    The acute form of the disease leads to fever, apathy, weakness, disturbances in movement coordination (= ataxia), jaundice (= icterus), tachycardia, cardiac arrhythmia and bleeding from the capillaries of the mucous membranes (= petechiae), which mainly occur on the underside of the tongue and on the conjunctiva of the eyelids. The temperature can rise to over 40 °C, the fever can last for one or several days. The animals are dull, become anaemic and show congested, sometimes icteric mucous membranes as a result of an occurring heart failure. Loss of condition and weight loss are the result. Sick animals can sway on the hindquarters and often show edema on limbs, abdomen and chest. pregnant mares can have abortions or weak foals. In case of therapy-resistant fever attacks as well as thrombocytopenia (= reduced number of thrombocytes), EIA should always be considered by differential diagnosis.

    The chronic form is characterized by fever attacks, fatigue and edema on the underside of the abdomen. The relapses, which occur at intervals of 4-6 weeks, last 2-5 days. After that, the animals are free of symptoms until a new flare-up occurs. With increasing duration of the disease, the animals develop anaemia and hypergammaglobulinemia (= increased blood gamma globulin content). They eventually become so weak that they can no longer stand. The animals become emaciated in spite of feed intake. An infected animal must be regarded as a lifelong virus carrier (persistent viremia) and potential virus excreter, regardless of whether clinical manifestation is observed. 30 to 90% of infections often continue for a very long time without any obvious symptoms. The anaemia that gives the disease its name is often not observed - it is caused by immunopathological decay of red blood cells.

    So far, there is neither a therapy nor an effective vaccine. The EIA is notifiable in all EU Member States and is one of the animal diseases notifiable to the World Organisation for Animal Health (OIE). When purchasing horses from anaemia regions, antibody detection should be carried out beforehand to exclude EIA.

    Diagnostics

    Suitable sample material for antibody tests is blood (serum).

    The diagnosis of EIA is based on serological detection methods of antibodies against the EIA virus (Coggins test or ELISA method), as the PCR method currently neither approaches the sensitivity and specificity of serological detection methods nor is it a routine method in the diagnosis of this disease. Antibodies are detectable by Coggins test at the earliest 2 to 3 weeks and rarely more than 60 days after infection.

    Positive cases can be confirmed by PCR (polymerase chain reaction). The conserved gag gene is used as target. However, neither the OIE nor the EU reference laboratory ANSES recommends a specific PCR method for the detection of EIA due to high genetic variability.

    Serum, EDTA blood and organ samples are suitable as sample material for the PCR examination. Equine viral arteritis, African horse sickness, piroplasmosis, babesiosis, ehrlichiosis, leptospirosis, petechial fever, kidney or heart disease, chronic bacterial infections, severe parasitic infestation or gastrointestinal catarrh must be considered for differential diagnosis.

    Contact, forms

    Institute of Veterinary Medicine Mödling

    Robert Koch-Gasse 17
    2340 Mödling

    Tel: +43 (0) 505 55-38112
    Fax: +43 (0) 505 55-38108
    E-Mail: vetmed.moedling@ages.at

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