Haemonchosis - Sheep

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Haemonchosis

Epidemiology of Haemonchosis

  • Haemonchus has a high biotic potential, egg to L3 development occurs very fast in hot humid conditions

Tropical and Subtropical Areas

  • Disease outbreaks depend on local rainfall
  • Parasite survives prolonged dry periods by arrested development
  • Development resumed just prior to rainy season e.g. Australia, Brazil, Middle East and Nigeria
  • Arrested development less common in areas with more frequent rainfall e.g. East Africa
  • Several cycles of infection annually

Temperate Areas (less favourable for Haemonchus L3 survival)

  • Ewe is primary source of infection (relatively few L3 overwinter on pasture)
  • Eggs hatch and develop to L3
  • Most L3 ingested by ewes and lambs in late summer become arrested (EL4, abomasal wall) → resume development following spring → acute haemonchosis (epidemiology equivalent to type 2 ostertagiosis)
  • A few L3 ingested by lambs do not become arrested → acute haemonchosis (if sufficient L3 ingested; equivalent to Type 1 ostertagiosis)
  • This is most likely to happen in hot thundery summer periods
  • Normally, only one cycle of infection annually

Pathogenesis of Haemonchosis

  • Moderate infection (2000 worms) leads to
    • Increased red blood cell turnover (from 4 months to 3 weeks)
    • Loss of haemoglobin and iron (normally recycled)
    • Depleted iron reserves leading to anaemia and death

Forms of Haemonchosis

  • Hyperacute (0-7 days)
    • Sudden death in apparently healthy sheep;
    • Severe anaemia (tropics mainly)
  • Acute (1-6 weeks)
    • Oedema, loss of condition, lethargy, death
    • Anaemia, hypoalbuminaemia
  • Chronic (2+ months)
    • Progressive weight loss or reduced weight gain
    • Similar appearance to poor nutrition

Diagnosis of Haemonchosis

  • Clinical signs (anaemia)
  • Season
  • Faecal egg count (may be very high)
  • Low blood haemoglobin, PCV and red blood cell count
  • Elevated blood pepsinogen
  • Post-mortem examination:
    • >2000 adult worms
    • Numerous haemorrhagic lesions on gastric mucosa
    • Brown fluid in abomasum
    • Pale oedematous carcass
    • Expansion of red marrow from epiphysis into medullary cavity of long bones