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== Introduction  ==

== Introduction  ==

''Haemonchus'' has a high biotic potential and egg to L3 development occurs very fast in hot humid conditions. In '''tropical and sub-tropical areas''', disease outbreaks depend on local rainfall. The parasite survives prolonged dry periods by arrested development which is resumed just prior to rainy season e.g. Australia, Brazil, Middle East and Nigeria. Arrested development is less common in areas with more frequent rainfall e.g. East Africa. There are several cycles of infection annually.

''Haemonchus'' has a high biotic potential and egg to L3 development occurs very fast in hot humid conditions. In '''tropical and sub-tropical areas''', disease outbreaks depend on local rainfall. The parasite survives prolonged dry periods by arrested development which is resumed just prior to rainy season e.g. Australia, Brazil, Middle East and Nigeria. Arrested development is less common in areas with more frequent rainfall e.g. East Africa. There are several cycles of infection annually.

In '''temperate regions''', the ewe is the primary source of infection (relatively few L3 overwinter on pasture) and eggs hatch and develop to L3. Most L3 ingested by ewes and lambs in late summer become arrested (EL4, abomasal wall) to then resume development following spring and cause acute haemonchosis (epidemiology equivalent to type 2 [[Ostertagiosis and Trichostrongylosis - Sheep|ostertagiosis]]). A few L3 ingested by lambs do not become arrested and immediately cause acute haemonchosis (if sufficient L3 ingested; equivalent to Type 1 ostertagiosis). This is most likely to happen in hot thundery summer periods. There is normally, only one cycle of infection annually in temperate areas.

In '''temperate regions''', the ewe is the primary source of infection (relatively few L3 overwinter on pasture) and eggs hatch and develop to L3. Most L3 ingested by ewes and lambs in late summer become arrested (EL4, abomasal wall) to then resume development following spring and cause acute haemonchosis (epidemiology equivalent to type 2 [[Ostertagiosis and Trichostrongylosis - Sheep|ostertagiosis]]). A few L3 ingested by lambs do not become arrested and immediately cause acute haemonchosis (if sufficient L3 ingested; equivalent to Type 1 ostertagiosis). This is most likely to happen in hot thundery summer periods. There is normally only one cycle of infection annually in temperate areas.

A moderate infection (2000 worms) leads to increased red blood cell turnover (from 4 months to 3 weeks) and a loss of haemoglobin and iron (normally recycled). Depleted iron reserves leading to [[:Category:Anaemia|anaemia]] and death.

A moderate infection (2000 worms) leads to increased red blood cell turnover (from 4 months to 3 weeks) and a loss of haemoglobin and iron (normally recycled). Depleted iron reserves leading to [[:Category:Anaemia|anaemia]] and death.

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[[Category:Gastric_Diseases_-_Sheep]] [[Category:Expert Review - Farm Animal]]

[[Category:Gastric_Diseases_-_Sheep]] [[Category:Expert Review - Farm Animal]]