Strongyloides ransomi: Factors Influencing the In vitro Development of the Free-Living Generation

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Abstract
Among the progeny of parasitic S. ransomi females, males did not appear in significant numbers until the 7th wk of infection in cases of single infection, and until the 3rd wk of infection in cases of multiple infection. The appearance of males was attributed to the effect of host [pig] immunity, the physiological aging of the parasitic females or both. Type of culture substrate and other cultural conditions did not influence the percent of larvae developing into males. Larvae sex was determined prior to hatching, probably during oogenesis or embryogenesis. Cultural conditions influenced the direction of development of female larvae. An initial pH < 5.9 or > 7.2 favored differentiation of larvae into infective larvae; intermediate initial pH levels favored development of free-living females. Baby pig substrate, autoclaved substrate and substrate washed free of soluble chemicals (adverse cultural conditions) promoted differentiation toward infective larvae. Adult pig substrate, nonautoclaved substrate and unwashed substrate promoted differentiation toward free-living females. Adverse conditions inside the host and favorable cultural conditions appear to favor an indirect life cycle.

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