Persistence of Hookworm Larvae in Soil

Abstract

Summary Eighteen enclosed units of soil were inoculated with equal numbers of hookworm eggs and dampened daily until larvae reached the infective stage. Half were then dampened daily and half left to dry until their turns came to be sampled. Sampling, which began on the 5th day in the wet series and on the 9th day in the dry, was progressive and cumulative, a new unit being added each day until all were under examination. Reduction in numbers in the wet series proved to be significantly more rapid than in the dry series, and on the five days when pairs of wet and dry cultures were sampled simultaneously, the dry cultures yielded 3 to 7 times as many larvae as the wet. When suspensions of infective larvae were poured onto damp soil, less than half of the larvae reached a depth sufficient to escape desiccation. The results substantiate the view that alternate wetting and drying of soil hastens the death of infective hookworm larvae. Thus, under usual conditions in well drained sandy regions, infective larvae remain viable on the surface for only a few minutes after rain ceases and in the absence of added contamination the soil becomes practically noninfective after brief periods of frequent rainfall.