Morphological Differences between Necator and Ancylostoma Larvae

Abstract

During 1924 in Peking and in Soochow, while carrying on some experimental work in connection with the investigation of the China Hookworm Commission, and in 1925, while working in the Parasitology Laboratory of the Peking Union Medical College, we have had an opportunity to examine large numbers of infective larvae of both species of hookworm which infect man, Ancylostoma duodenale and Necator americanus, as well as those of the dog species, Ancylostoma caninum. At the suggestion of Drs. W. W. Cort and N. R. Stoll of the China Hookworm Commission, a careful study was undertaken to ascertain whether some clearly definable morphological distinctions exist between these larvae, which would make it possible to determine the species of hookworm present in fecal cultures and in polluted soil. This investigation was considered to be the more valuable, since in surveys which precede campaigns for the control of hookworm disease it is of great importance to obtain information concerning the type and degree of soil infestation as well as of infection existing in the population. Darling's (1922) method of choosing a representative and sufficiently large group of the population, to which he administered an anthelmintic, and then counting and identifying the worms expelled during seventy-two hours following the treatment, undoubtedly gives the most exact information regarding the species present. Serious difficulties, however, are encountered in the application of this method because of the great expense involved, the skilled work required, and the difficulty in securing cooperation from the population. It is, therefore, important that methods be found which give the same information ;.s Darling's method but which are more easily applicable as far as expense and cooperation from the population are concerned. The egg-count method devised by Stoll (1923) enables the worker in a preliminary survey to estimate fairly accurately the degree of infection in any group of people. It can be handled easily even by purely mechanically trained assistants, is not expensive, and for a rough estimate does not require more cooperation from the population than the delivery of a single fecal sample per person. However, it has the disadvantage, compared with Darling's method, that no information can be gained regarding the species of hookworm involved.