Development of an in vitro culture method for harvesting the free-living infective larvae of Strongyloides venezuelensis.

Abstract

An in vitro culture technique was established for harvesting Strongyloides venezuelensis free-living infective larvae using a nutrient broth medium as a substitute for rat-feces in polyvinyl culture bags (10 x 12 cm). The egg hatch rate (Y) in sterile saline at different incubation temperatures (X) was expressed as the quadratic function, Y = -0.192X2 + 8.673X - 19.550 (r = 0.901). The highest (100%) egghatch rate was observed at 25 degrees C. A significant difference (p < 0.05) in development rate (Y) of free-living infective larvae was observed between different concentrations of nutrient broth (X) which was highest (20.6%) in 0.12% nutrient broth concentrations, incubated at 20 degrees C for 5 days [Y = -864.032X2 + 245.995X - 0.560 (r = 0.875)]. Yields (Y) of infective larvae were observed relatively high when the culture medium was incubated at higher temperatures (X) which peaked at 25 degrees C (20.0%) than at lower temperatures, 15 degrees C (10.9%) and 20 degrees C (18.1%) [Y = -0.189X2 + 8.387X - 72.795 (r = 0.981)]. The period (Y) required for the development of infective larvae decreased with higher incubation temperatures (X) [Y = 0.035X2 - 2.025X + 32.375 (r = 0.995)]. The highest yield (19.2%) of infective larvae was obtained from culture bag inoculated with 15,000 eggs than with below and over 15,000 eggs in 0.12% nutrient broth and incubated at 25 degrees C for 4 days. The newly adapted culture method (from egg to third-stage larva) may be useful as a bio-bar/bioassay system for screening new chemical products, anthelmintics and pesticides, as well as for parasito-immunological studies with Strongyloides species.