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.
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.