Stronglyoides ransomi: factors influencing the in vitro development of the free-living generation.

Among the progeny of parasitic females of Strongyloides ransomi, ransomi, males did not appear in significant numbers until the 7th week of infection in cases of simple infection, and until the 3rd week of infection in cases of multiple infection. The appearance of males was attributed to the effect of host immunity, the physiological ageing of the parasitic females, or both. Type of culture substrate and other cultural conditions did not influence the percent of larvae developing into males. Sex of larvae was determined prior to hatching, probably during oogenesis or embryogenesis. Culture conditions influenced the direction of development of female larvae. An initial pH below 5.9 or above 7.2 favored differentiation of larvae into infective larvae, whereas, 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. In general, adverse conditions inside the host and favor an indirect life cycle.