Synonyms: Swamp Fever, EIA
It is a chronic persisting infectious viral disease of equines characterised by emaciation, anaemia, intermittent fever and generalised lymphoproliferative changes and oedema. The anaemia may be for few days or may persist for a longer period and this is considered to be immunologically induced problem.
Distribution
It is first reported in France in 1843. Since then it is reported from all over continents but seen in significant proportion in Central America and South America. Japan and Australia are considered as places of predominance. United states and Canada are not free from this disease. Incidence seems to be very low in Australia. The disease has been reported from Karnataka, India in 1987 in thorough bred race horses.
Aetiology
For the precipitation of this disease some predisposing factores like malnutrition, debility, helminthiasis and stress of monsoon and summer have been categorised. The actual cause of this disease is a virus which belongs to lentivirinae subfamily of the Retroviridae family. It is a RNA virus and this virus has got resemblance with human AIDS virus. There are number of serotypes which vary antigenically and from virulance stand point. The virus can be cultivated in tissue culture and the virus can be killed by exposing them to heat and commonly available house detergents. There is huge antigenic dift in the surface glycoprotein and emergence of novel antigenic strain is responsible for the relapse of the fever.
Susceptible Hosts
It is predominantly the disease of equidae family. Mules, donkeys are also affected. The disease has also been recorded in sheep, rabbit and cockrels.
Clinical Findings
The disease has got a long incubation period following infection and it ranges from 1 to 4 weeks. The disease has got varied clinical manifestation characterised by anorexia, pyrexia, depression, dullness, oedema of ventral abdomen, brisket, fore and hindleg, dyspnoea, tachycardia, jaundice, anaemia, petechial haemorrhage, muscular weakness, exhaustation, recurrent mild fever etc. Animals may show temporary recovery but there is possibility of relapse after few weeks. Animals, where persistence of infections continues for long time may remain in debilitated condition but they suffer from allotriophagia. Such animals may remain as carrier. Death is due to anoxic anaemia or cardiac failure. The pregnant animal may abort.
Lesions
The entire carass of the animal may show subcutaneous oedema and submucosal and subserous haemorrhages. There is generalised lymphadenopathy. Liver is considerably enlarged and such is the condition of the spleen. Necrotizing vasculitis of different organs are the principal lesions of this disease.
Diagnosis
Diagnosis is based on history, clinical signs and laboratory tests. Confirmation of the disease is made by Coggin’s agar gel immunodiffusion test. Commercial kit for such test is available. Precipitating antibody is demonstrated through this test. ELISA has recently been introduced and considered as alternative test to AGID test.
Haematological studies can be made to know about the changes in the blood components due to this disease. Haemogram may reveal a picture of normocytic normochromic anaemia, leukopenia, fall of PCV, neutropenia, thrombocytopaenia and elevated Heinz body and icterus index.
Differential Diagnosis
The disease can be confused with some other diseases of horse where anaemia is the important clinical picture. Haemoprotozoan infections like babesiosis, trypanosomiasis should be ruled out through peripheral blood examination and AGID or ELISA. Diseases like purpura haemorrhagica and leptospirosis should also be ruled out. Viral arteritis may have clinical resemblance but can be differentiated by looking at the ocular changes characterised by palpebral oedema, photophobia and lachrymation.
Treatment
There is no specific treatment against this malady. However, symptomatic treatment with febrifuge, digitalis, anabolics and protein hydrolysate may be extended. In severe anaemic patient whole blood transfusion followed by haematinic preparation either through parenteral or oral routes are useful adjunct against this disease.
Control
All possible care should be undertaken to limit the movements of carrier animals. Suspected animals should be isolated and serological test should be done to identify the disease. If possible the animal may be destroyed. Importation of animal should be made with judicious approach. Many a time carrier animal may pose a serious problem in disease free countries through their introduction. Arrangement for strict quarantine of imported horse and there serological test should be strictly followed.
The disease is mostly prevalent in swampy areas and therefore such places should be avoided for equine rearing.
Since the disease is concerned with vector population therefore, strict measure to control the vector population be undertaken. Strict drainage, cleaning and disinfection of the stable is very much necessary.
Collection of blood sample as well as injection and inoculation should be done with disposable syringe.
Vaccine is not practicable due to various subtypes of the virus.
