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Population dynamics of snail infection by miracidia

Published online by Cambridge University Press:  06 April 2009

R. M. Anderson
R. M. Anderson
Affiliation:
King's College, London University, Strand, London WC2R 2LS
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Summary

The essential biological features of snail infection by miracidia are incorporated into a simple model which describes the rate of change with respect to time of the number of miracidial infections/host. The model is based on the assumption that the net rate of infection is directly proportional to the density of both miracidia and hosts. Empirical evidence is provided to support this assumption. The basic framework of the model is expanded to take into account demographic stochasticity in infection and is used to predict the percentage of snails that become infected after exposure to a known number of miracidia for a set period of time. The influence of miracidial mortalities and age-dependent infectivity are examined and theoretical predictions are compared with a range of experimental results.

Underlying heterogeneity in the distribution of the number of infections/snail is shown to generate an artifactual decrease in infection rates as exposure density rises, if rate estimation procedures are based on an assumption of randomness. Empirical evidence is presented to illustrate the generation of over-dispersion in the number of miracidial infections/snail under tightly controlled laboratory conditions, using supposedly homogeneous snail populations.

Biological causes for underlying patterns of heterogeneity are discussed in relation to snail susceptibility to infection and ‘attractiveness’ to infective stages.

Type
Research Article
Information
Parasitology , Volume 77 , Issue 2 , October 1978 , pp. 201 - 224
Copyright
Copyright © Cambridge University Press 1978

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References

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