The community ecology of soil-transmitted helminth infections of humans in a hyperendemic area of southern Nigeria

A parasitological survey of two rural villages in southern Nigeria, involving 6842 stool samples, showed that 78·3% of the population harboured soil-transmitted intestinal nematodes. Among these people the commonest infection (71·1%) was with Necator americanus and Ancylostoma duodenate, 20·6% of infections were with Ascaris lumbricoides, 7·9% with Trichuris trichiura and 0·4% with Strongyloides stercoralis. Mixed infections were common. No trematode or cestode infections were found.The focus of infection was familial, the sources of infection being contaminated fields around households which lacked pit-latrines, and possibly also around schools because of indiscriminate defaecation. The pattern of worm burdens in the population approached a negative binomial, a few individuals carrying a very heavy share of the total worm load in the community. The prevalence and worm burden were also markedly related to age and especially to season, infections being highest in children and during the rainy season. A model is pioposed for the control of helminthiases based on these results.