Difference between revisions of "Haemonchosis - Sheep"
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(Created page with '=== Haemonchosis === *''Haemonchus contortus'' (abomasum) **2cm long,'''barber's pole''' appearance when fresh **Primarily a tropical/sub-tropical parasite, although may cause pr…') |
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==== Epidemiology of Haemonchosis ==== | ==== Epidemiology of Haemonchosis ==== | ||
Revision as of 21:55, 21 April 2010
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