The relationship between the frequency distribution of Ascaris lumbricoides and the prevalence and intensity of infection in human communities.
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.
Guyatt
H L
HL
Department of Biology, Imperial College, University of London.
Bundy
D A
DA
Medley
G F
GF
Grenfell
B T
BT
D000818:Animals; D001196:Ascariasis / Q000453:epidemiology* / Q000469:parasitology; D001200:Ascaris / Q000254:growth & development*; D016010:Binomial Distribution; D003430:Cross-Sectional Studies; D006801:Humans; D015995:Prevalence; D011336:Probability