Necator americanus: population structure, distribution, and fluctuations in population densities of infective larvae in contaminated farmlands.

Observations have been made over a 15-month period on the frequency distribution of human faecal deposits and infective larvae of Necator americanus in a hookworm endemic area. The agestructure of infective larvae in a field population and their vertical distribution in soils were determined. These studies were undertaken to examine the hypothesis that hookworm transmission in the tropics is discontinuous and limited mainly to the rainy season. The distribution of larvae was found to be overdispersed statistically and in general much greater numbers of L3s were recovered during the rainy season. The degree of overdispersion was also reduced during this season, and there was a tendency for larvae to be confined to the surface/topsoil. The implications of these findings have been discussed in relation to human hookworm parasitism in endemic areas of the tropics.