The Ova-Parasite Ratio for Ancylostoma duodenale and Ascaris lumbricoides

Abstract

I. OVA-PARASITE RATIO FOR Ancylostoma dutodenale Stoll (1922-23) devised a method for counting hookworm ova in feces and determined the relation between the number of ova per gram of excrement and the number of female worms, Necator americanus, harborbed by the host. This ratio varied from 44 eggs per gram per female worm on formed feces, to 25 eggs per female on mushy stools, to 12 eggs per gram per female worm on diarrhoeic stools. The same factors have since been found to hold for this parasite, by Sweet (1925) in Ceylon, and by Manalang (1927) in the Philippine Islands. So far there is but little information of this relationship for the old world hookworm, Ancylostoma duodenale, the majority of observations having been made on mixed infections with N. amtericanus. Darling (1922) on the basis of a few comparative flotation egg counts and worm counts believed that A. duodenale produced a larger number of eggs than N. americanus and Sweet (1924) pointed out, largely on theoretical grounds, that the egg production of A. duodenale may be about five times as great as N. americanus. Cort, Grant and Stoll (1926) reported from a study of about fifty Chinese cases of mixed infections, three-fifths A. duodenale and two-fifths N. americanus, that the number of eggs per gram per female worm is about 200. This figure makes the egg output for A. duodenate about three times that found by Stoll (1923) in pure infections with N. americanus in Porto Rico. Soper (1927) from a statistical analysis of four Paraguayan hookworm cases with N. americanus and A. duodenale (three mixed infections and one pure Necator) concluded that the average egg output per day of A. duodenale is between two and two and one-half that of N. americanus.