Equine infectious anaemia
Equine infectious anemia (EIA), an acute or chronic viral disease of the equines, shows intermittent fever, loss of weight, depression, progressive weakness, oedma and anaemia. The virus belongs to the genus Lentivirus in the family Retroviridae. Horses, mules and donkeys are susceptible to EIA in the order of listing. EIA has been previously reported in 1987 from thoroughbred horses in India. However, no incidence of EIA has been reported from India since 1997.
Epidemiology: The virus is found in the blood, milk and semen of the affected animal. Outbreaks among animals frequently coincide with the seasonal activity of various biting flies and mosquitoes. Transmission is through inoculation of virulent blood into or under the skin either by insects, blood transfusion, contaminated needles, stomach tubes or by accident. The incidence of the disease is directly related to the density of biting insects (i.e. stable fly and Tabanus species fly) in the area. Hence, horses in marshy areas are more prone to insect biting and to this disease (swamp fever). The infected horses remain viraemic carrier for life and they become potential excretor of virus, even in absence of clinical disease.. The virus shows considerable resistance to chemical disinfectants, heating, freezing and drying.
Symptoms: The incubation period usually ranges from 1 to 3 weeks but in some case may extend upto 3 months. The acute form shows viraemia, high fever and profuse sweating. The characteristics of the subacute and chronic forms are intermittent fever, anaemia, emaciation, oedema of dependent parts and marked depression. Mortality varies from 30 to 70% of the affected animals in the per acute and acute forms.
Diagnosis: EIA is diagnosed on the basis of clinical symptoms, blood examination and gross pathology. However, the most certain method of diagnosis is to inoculate susceptible young, healthy horses with the whole blood or buffy coat of the suspected animal. Serologic tests, viz. immunodiffusion test (Coggins test) and ELISA using P26 antigen or western blot besides virus isolation provide a confirmatory diagnosis.
Prevention and control: In our country, it is mandatory to test all the horses participating in race courses by Coggins test for EIA. It is also mandatory to test all the horses quarantined before importing and exporting of horses. Infected horses and horses that are apparently healthy but positive by Coggins test should be destroyed. The affected animal should be isolated at least 200 meters away be killed and disposed off by cremation or deep burial after diagnosis. No vaccination and not treatment is recommended for EIA.