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Host immunity often reduces egg production by female worms. This results in a stereotyped pattern of worm egg output, regardless of the level of infection.
 
Host immunity often reduces egg production by female worms. This results in a stereotyped pattern of worm egg output, regardless of the level of infection.
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'''Factors Adversely Affecting Host Immunity''':
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a) ''Nutrition'':
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Gross deficiency; mineral/trace element deficiency, e.g. cobalt.
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b) ''Reproductive status'':
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"Periparturient relaxation in immunity" (PPRI) seen in breeding ewes and sows. Due to impaired cell-mediated immune response - associated with an increase in blood prolactin levels/shift of IgA from gut mucosa to mammary gland around parturition?
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c) ''Drug treatment'':
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e.g. repeated anthelmintic and corticosteroid treatment.
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d) ''Concurrent infection'':
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e.g. pathogenic effects of ''Nematodirus'' infection exacerbated by coccidia in lambs.
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e) ''Previous experience of a parasite'':
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e.g. hypersensitivity reaction to ''Haemonchus'' in some ewes.
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