Age specific patterns of change in the dynamics of Wuchereria bancrofti infection in Papau New Guinea

Results of a longitudinal study of the age-specific dynamics of Wuchereria bancrofti infection in a community of East Sepik Province, Papua New Guinea (PNG) are described. Microfilarial (mf) density and serum levels of W. bancrofti phosphorylcholine-containing antigen (PC-Ag) in individuals were used as indirect measures of adult worm burden. These parasitological data were collected from 126 subjects > 4 years of age at two time points, 12 months apart, prior to the administration of the antifilarial drug diethylcarbamazine (DEC). No significant changes in levels of mf density were observed for the study population between these two time points. However, significant changes in the levels of circulating PC-Ag were noted in subjects ≤ 20 years of age, but not in subjects > 20 years of age, between these two time points. The apparent shorter half life of circulating PC-Ag compared to that of mf makes antigenemia a more sensitive measure of the dynamics of adult worm populations. These data are discussed in terms of a basic mathematical model describing the dynamics of adult worm populations in relation to their life expectancy and attrition of larvae during establishment. Consideration of these data in the context of this simple immigration/death model suggests that the differences observed in patterns of change in intensity of infection between subjects ≤ 20 years old and those > 20 years old may be consistent with the acquisition of resistance to superinfection with increasing age.