The epidemiology of Ascaris lumbricoides, Trichuris trichiura, and hookworm in children in the Ranomafana rainforest, Madagascar.

An epidemiological study of intestinal nematodes was conducted with 1,292 children, ranging from birth through 11 yr old, living in the Ranomafana rainforest of southeast Madagascar. Fecal examinations revealed prevalences of 78% for Ascaris lumbricoides, 38% for Trichuris trichiura, 16% for hookworm, and 0.4% for Schistosoma mansoni. Infection intensity was measured indirectly by fecal egg counts and directly by A. lumbricoides expulsion following treatment with pyrantel pamoate. The mean A. lumbricoides worm burden for children, 5-11 yr old, was 19.2 (SD 20.4) worms per child, with a median of 13 worms (n = 428). The distributions were overdispersed for all 3 nematodes. The age profiles showed a rapid acquisition of A. lumbricoides during infancy, increasing to 100% prevalence by age 10. After mebendazole anthelmintic treatment and a 12-mo reinfection period, the nematodes had rebounded to pretreatment prevalence and intensity levels. There was evidence for age-dependent predisposition of the children to infection intensity for each of the 3 nematodes. Dual species intensity correlation was consistently strong for A. lumbricoides and T. trichiura. The significantly higher prevalence and intensity of ascariasis in girls were thought to be related to exposure.