Abstract
In human and animal infections with Strongyloides stercoralis several undetermined factors operate to produce a variability and instability of the strains of the organism. 1 Possibly the presence of parasitic male worms during the period between adolescence and maturity of the parasitic females may play an important part in determining the type of their progeny. 2 In order to obtain information on the fecundity of the parasitic females, we have inoculated 17 dogs with 5 known human strains of Strongyloides stercoralis and a rhesus monkey with a chimpanzee strain. The abdominal skin, the buccal cavity and the intracecal mucosa were used as sites of entry for the infective stage (filariform) larvae. Detailed information was obtained concerning the source, type and number of larvae in each inoculum, the prepatent period, the daily number of Strongyloides eggs or larvae recovered from the feces, and, on sacrificing the host, the position, number and condition of the parasitic females. The prepatent periods usually ranged from 11 to 18 days, although one dog was positive on the fifth day, one was not detected until the 143rd day and one apparently never passed larvae in the stools.
The number of eggs produced has been shown to rise rapidly to a maximum, after which it declines to a lower level which is maintained for a time and then is gradually reduced to a base level of zero. Culture of larvae in the feces, as recommended by Sandground, 3 is a poor index of production of progeny, because so many larvae are passed in a non-viable condition. Likewise, samplings of less than 5 gm. of feces daily are frequently inadequate to detect the larvae present. Even then great care is needed to discover and identify disintegrating larvae, which frequently number 5 to 90% of the total yield.
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