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Viral Disease - Equine Infectious Anaemia

Synonyms

Swamp Fever, Equine malarial fever

Definition

Acute infectious disease equine characterized by high fever, anemia, progressive weakness and debility and jaundice, edema and haemorrhages

Etiology

Lentivirus, Virus shares serological reactivity with human AIDS lentivirus

Incidence

First recorded in India in 1987 in a equine stud farm at Bangalore

Seropositive horses in Haryana and Maharashtra.

Transmission

Mechanically by biting insects like mosquitoes, Tabanus sp., Stomaxys sp.

Iatrogenic transmission by transfer of minute amounts of blood from infected horses to normal horses by use of unsterile hypodermic needles, tattoo needles, etc.

Not spread by contact

Disease is more prevalent in swampy areas (insect breeding)

Pathogenesis

Virus localizes in various organs like spleen, liver, kidney and lymphnodes

Virus enters and infects macrophages causes destruction of macrophages - release of virus , production of antibodies, to antigenic components; formation of antigen-antibody complexes which induce fever, glomerulitis and complement depletion

Specific complexes causes hemolysis and phagocytosis by activating reticulo-endothelial system

Pathological processes subside as virus neutralizing antibodies prevent multiplication in macrophages and horses become permanently asymptomatic

Life-long viral persistence

EIA virus tries to avoid host's immune response by undergoing rapid variation

Their survival depend on the neutralizing antibodies in horse serum

The appearance of new antigenic variants leads to clinical relapse

Anaemia is caused by destruction of RBCs by means of immunologically mediated mechanisms

Erythrocytes of infected horses are coated with antiviral antibodies and complement

This binding to the cell surface results in increased osmotic fragility and erythrophagocytosis

Plasma haemoglobin level increases and liver haptoglobin decreases which binds to haemoglobin

Hemolysis is the main factor causing anaemia

Clinical Signs

Acute

Rapid onset of high fever (upto 108˚F)

Extreme weakness

Excessive thirst

Anorexia

Depression

Profuse perspiration

Sublingual or nasal haemorrhages and edema in lower abdomen

Anemia-RBC count falls to 4 million /cubic mm

Death within a month, if the animal survives -sub acute or chronic form

The lesion are edema and haemorrhages on heart

Spleen: Increase in red pulp and infiltration with immature mononuclear cells

Infiltration of immature lymphocytes in interstitium of kidneys

Immunoglobulin's and complements are demonstrated by immunofluorescence in glomeruli of kidneys

All organs show reticulo- endothelial hyperplasia

Sub-acute

Relapsing fever

Other signs similar to acute type

Anemia -RBC count falls to 1.5 million /cubic mm

ESR increased

The lesions are Hyaline degeneration and lymphocytic infiltration of myocardium

Congestion of central vein and sinusoids of liver with infiltration of lymphocytes, plasma cells, macrophages laden with haemosiderin

Hyperplasia of reticulo-endothelial cells in spleen and lymph nodes

Small number of lymphocytes in kidneys

Haemorrhages in bone marrow

Chronic

Intermittent fever

Edema of under thorax and abdomen

Debility/depression

The lesions are Myeloid and erythroid elements are in normal proportion indicating that haemopoiesis is activated

Haematological Changes

'NORMOCYTIC AND NORMOCHROMIC ANAEMIA'

Diagnosis

Clinical signs & lesions

Isolation and identification of the virus in leucocytic culture

Agar immunodiffusion test developed by Coggins in 1972 is used to detect antibodiesin serum

Immunofluorescence test in tissues to demonstrate antigens

Differential diagnosis

Acute disease

Purpura hemorrhagica

Babesiosis

Equine granulocytic ehrlichiosis

Equine viral arteritis

Autoimmune hemolytic anemia

Leptospirosis

Parasitism

Idiopathic thrombocytopenia,

Chronic disease

Internal abscessation (metastatic

Streptococcus equi infection

Chronic inflammatory disease, neoplasia and chronic hepatitis.

Treatment

No specific treatment is available.

Supportive treatment including blood transfusions and hematinic drugs may facilitate clinical recovery but it is important to remember that recovered horses are persistently infected and infectious for life.

Control

Control of EIA is based on identification and eradication or life-long quarantine of infected animals, quarantine and testing of new stock, compulsory testing of imported horses, and efforts to prevent spread of the virus by controlling insect access to horses and use of strict hygiene when vaccinating or collecting blood samples from horses.


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