Guyatt H L, Bundy D A, Medley G F, Grenfell B T
Department of Biology, Imperial College, University of London.
Parasitology. 1990 Aug;101 Pt 1:139-43. doi: 10.1017/s0031182000079841.
Observed field data from a range of geographically distinct human communities suggest a consistent non-linear relationship between prevalence and mean intensity of Ascaris lumbricoides infection. Utilizing the negative binomial distribution as a description of observed aggregation, maximum-likelihood analysis reveals that the degree of aggregation is a negative linear function of mean worm burden. The factors responsible for this relationship in human populations require further study but may involve some combination of (i) density-dependent reduction in worm numbers within individuals, (ii) density-dependent parasite-induced host mortality or (iii) self-treatment by heavily infected hosts. Variability in the degree of aggregation appears dependent on the level of infection in a community and independent of geographical differences in the host or parasite populations.
