Genetic analysis of susceptibility to infection with Ascaris lumbricoides

Epidemiologic studies of helminthic infections have shown that susceptibili ty to these parasites frequently aggregates in families, suggesting the pos sible involvement of genetic factors. This paper presents a genetic epidemi ologic analysis of Ascaris lumbricoides infection in the Jirel population o f eastern Nepal. A total of 1,261 individuals belonging to a single pedigre e were assessed for intensity of Ascaris infection at two time points. Foll owing an initial assessment in which all individuals were treated with albe ndazole, a follow-up examination was performed one year later to evaluate r einfection patterns. Three measures of worm burden were analyzed, including eggs per gram of feces, direct worm counts, and worm biomass (weight), For all traits, variance component analysis of the familial data provided uneq uivocal evidence for a strong genetic component accounting for between 30% and 50% of the variation in worm burden. Shared environmental (i.e., common household) effects account for;between 3% and 13% of the total phenotypic variance.