The Panama Strains of Human Strongyloides.

Abstract

The studies of Grassi, 1 Perroncito 2 and particularly those of Leuckhart 3 demonstrated that there were 2 different strains of the human Strongyloides, S. stercoralis, the one consisting entirely of a parasitic generation and the other having both a parasitic and a free-living generation in its life cycle. Leichtenstern 4 believed that the organism in warm climates utilized only the indirect development, while those in cooler regions utilized only direct development. This hypothesis, however, has been proved fallacious by the work of Darling, 5 Sandground, 6 Nishigori 7 and others.

Darling's series consisted of cultures from 23 infected persons in Panama, residents of the tropics for many years. Of these cultures 5 proved to be purely indirect in their development, 7 were direct only and 11 were combined strains.

During the summer of 1930 the writer studied 1662 native patients in the Santo Tomas Hospital, Panama, of whom 348 were positive for Strongyloides stercoralis. Of this series 276 were each examined 3 or more times. Twenty-nine of these (10.5%) were of clinical importance. From the entire series 27 cases of heavy infection, in which no hookworm infestation was present, were selected for culture. These cultures consisted of active larvae, which had been richly concentrated by the centrifuge method, planted on animal charcoal in sterile Petri dishes, and allowed to develop at room temperature (26-36°C.). Each culture was examined daily for a period of from 3 to 9 weeks.

In 5 cases second cultures were made from the same individuals and in every instance these were similar to the original strains. In the indirect type filariform larvae of the free-living generation had developed as early as the sixth day of culture; by the fifteenth day the strain had completely died out. In the unmodified direct type the rhabditiform larvae of the parasitic generation grew rapidly, became ensheathed between the fourth. and sixth day, and continued as active organisms up to 9 weeks, without exsheathing or metamorphosing.