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The population biology of the parasitic stages of Haemonchus contortus

Published online by Cambridge University Press:  06 April 2009

Gary Smith
Gary Smith
Affiliation:
School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, 382 W. Street M, Kemiett Square, PA 19348, USA
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Summary

The population biology of the parasitic phase of the Haemonchus contortus life-cycle is discussed within the context of a mathematical model of those processes which regulate population density. Parasite death is assumed to be attributable to at least three processes: failure of the 3rd-stage larvae (L3) to exsheath following ingestion, failure to become established following exsheathment (immune exclusion), and mortality of 4th- and 5th-stage worms on the mucosal surface. The proportion of worms which avoid immune exclusion is a declining sigmoidal function of the duration of infection, at least under conditions of continual exposure to L3 larvae. Under the same conditions, the death rate of 4th- and 5thstage worms can be modelled as an increasing linear function of the host's experience of 3rd stage larvae. The model provides a good description of the worm burdens observed during the course of a long-term trickle infection experiment even though a priori arguments indicate that it would be an inadequate representation of events in the field.

Type
Research Article
Information
Parasitology , Volume 96 , Issue 1 , February 1988 , pp. 185 - 195
Copyright
Copyright © Cambridge University Press 1988

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