The Length of Life and the Rate of Loss of the Hookworms, Ancylostoma Duodenale and Necator Americanus

Abstract

Summary Pure cultures of A. duodenale and N. americanus larvae were prepared in sterile sand from mascerated adult females of the two species. Ancylostome infections were transmitted through the skin to 20 volunteers, and necator infections to five volunteers. Repeated attempts to establish necator infections by the oral route in five other volunteers failed completely. The period between the application of larvae to the skin and the appearance of ova in the stools averaged 53 days, determined by weekly, not daily, examinations. A large group of hookworm-free “controls” was periodically examined during the course of this investigation to determine whether natural infections were being acquired from the soil of the jail compound. Since not a single “control” was ever found infected it was concluded that no natural infection was being acquired from the same soil by the experimentally infected volunteers. The percentage of larvae that penetrated the skin and finally reached maturity varied greatly in different individuals, but this appeared to have no relation to previous infection or to the age of the host. Three of these ancylostome infestations and one necator infestation were followed throughout their existence by means of the egg count and the direct centrifugal flotation method to determine the longevity and rate of loss of the two species. Several other cases were studied for periods of three to five years. The appearance of ova in the feces was followed by a gradual increase in the egg output, until a peak was reached in from 12 to 18 months. This was followed by a decline of 50 to 70 per cent in egg production within a period of three to six months. The maximum period from the date of infection to the disappearance of ova in the feces of the ancylostome patients was 81 months; the average for three patients was 76 months. In the only necator case that was under observation throughout the course of infection the egg count was positive for only 12 months, but ova were detected by direct centrifugal flotation method 64 months after the date of infection. Graphs were prepared to show the trend of the egg output curves in nine cases, and the prominent features of these and of graphs prepared from studies on other human cases and on dogs are compared and discussed.