Equine infectious anaemia

EQUINE INFECTIOUS ANAEMIA

Synonyms

  • Swamp Fever, Equine malarial fever

Definition

  • Acute infectious disease equine characterised by high fever, anaemia, progressive weakness and debility and jaundice, oedema and haemorrhages as main gross lesions

Etiology

  • Lentivirus
  • Virus shares serological reactivity with human AIDS lentivirus
  • Virus persists in blood through out the life

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 through unsterile hypodermic needles, tattoo needles, etc.
  • Not spread by contact
  • Disease is more prevalent in swampy areas (insect breeding)

Pathogenesis

  • Virus localises in various organs like spleen, liver, kidney and lymphnodes
  • Virus is detected in greater quantities in severe attacks
  • It disappears from tissues in periods between attacks
  • Although there is persistent viraemia, throughout the horse life the virus level is low except during periods of clinical activity, so it is at this time the animal is highly infective
  • Virus enters and infects macrophages causes destruction of macrophages and 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 neutralising antibodies prevent multiplication in macrophages and horses become permanently asymptomatic
  • Life-long viral persistence is due to viral induced defect of the macrophages
  • EIA virus tries to avoid host's immune response by undergoing rapid variation in antigenicity
  • Erythrocytes of infected horses are coated with antiviral antibodies and complement causes increased osmotic fragility and erythrophagocytosis - Anaemia

Clinical signs

Acute

Subacute

Chronic

  • Rapid onset of high fever (upto 108˚F)
  • Extreme weakness
  • Excessive thirst
  • Anorexia
  • Depression
  • Profuse perspiration depression
  • Sublingual or nasal haemorrhages
  • Oedema – lower abdomen
  • Anaemia -RBC count falls to4 million /cubic mm
  • Death within a month
  • If the animal survives -subacute or chronic form

  • Relapsing fever
  • Other signs similar to acute type
  • Anaemia -RBC count falls to 1.5 million /cubic mm
  • ESR increased
  • Intermittent fever
  • Oedema of under thorax and abdomen
  • Debility/depression

Gross lesions

  • Acute form
    • Icterus, oedema and haemorrhages of membranes of various organs
    • Oedema on the ventral wall of abdomen, at the base of the heart and perineal fat
    • Petechial or ecchymotic haemorrhages in pleura and peritoneum
    • Heart is enlarged, pale and flabby
    • Haemorrhages on epicardium and pericardium
    • Clear serosanguinous fluid in pericardium
    • Enlarged liver and spleen with haemorrhages sometimes with infarcts 
    • Lymph nodes are enlarged
    • Bonemarrow is strikingly red indicating active haemopoeisis
    • Kidneys are oedematous
  • Subacute form
    • Anaemia is very prominent than oedema
    • Spleen is enlarged
    • Liver is enlarged , dark brown and hard to incise
    • Muscles are pale
  • Chronic form
    • Hypertrophy of spleen and bonemarrow

Microscopical lesions

  • Acute form
    • Oedema and haemorrhages on heart
    • Increase in red pulp and infiltration with immature mononuclear cells
    • Infiltration of immature lymphocytes in interstitium of kidneys
    • Immunoglobulins and complements are demonstrated by immunofluorescence in glomeruli of kidneys
    • All organs show reticulo- endothelial hyperplasia
  • Subacute form
    • Hyaline degeneration and lymphocytic infiltration of myocardium
    • Congestion of central vein and sinusoids of liver with infiltration of lymphocytes, plasmacells, macrophages laden with haemosiderin
    • Reticulo-endothelial cells form small nodules in sinusoids
    • Hyperplasia of reticulo-endothelial cells  in spleen and lymph nodes
    • Small number of lymphocytes in kidneys
    • Haemorrhages in bone marrow
  • Chronic form
    • 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

Last modified: Saturday, 17 December 2011, 10:04 AM