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A stochastic model for the aggregation of Onchocerca volvulus in nodules

Published online by Cambridge University Press:  31 July 2001

H. P. DUERR ,
K. DIETZ ,
D. W. BÜTTNER  and
H. SCHULZ-KEY
H. P. DUERR
Affiliation:
Department of Medical Biometry, University of Tübingen, Germany Institute of Tropical Medicine, University of Tübingen, Germany
K. DIETZ
Affiliation:
Department of Medical Biometry, University of Tübingen, Germany
D. W. BÜTTNER
Affiliation:
Bernhard Nocht Institute of Tropical Medicine, Hamburg, Germany
H. SCHULZ-KEY
Affiliation:
Institute of Tropical Medicine, University of Tübingen, Germany
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Abstract

A model is presented which describes the aggregation of female Onchocerca volvulus in nodules and their distribution in the human population. The basic model is based on a single parameter, the formation probability q, which represents the probability with which incoming larvae form a new nodule. This parameter describes parasite behaviour which cannot easily be recognized in available data without modelling. The estimate for the average formation probability of μq = 0.39 suggests an attraction of the invading infective larvae to already existing nodules or resident worms with probability 0.61. No significant difference in μq was found between the forest and savanna parasite strains. The model can be used inversely to estimate the worm burden of persons from palpation data. The observed variance in the number of nodules per person requires the assumption of a variance-increasing mechanism which was implemented by heterogeneity within the host population (extended model with 2 parameters). Possible reasons for this heterogeneity are presented and its implications concerning the reproductive biology of the parasite are discussed.

Keywords

Onchocerca volvulussavanna and forest strainsaggregationmodellingonchocercomatanodule formation
Type
Research Article
Information
Parasitology , Volume 123 , Issue 2 , August 2001 , pp. 193 - 201
Copyright
2001 Cambridge University Press

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