From a study of strongyloides infections in man and animals in this region, it has been determined, in confirmation of the view of Grassi, Calmette, and others, that they are not causative factors in the production of diarrhea. The mother worm, however, burrows into the mucosa and deposits her ova there. Certain tissue reactions take place and are evidenced by the cellular proliferation in those portions of the intestines occupied by the nematodes.
In animals, there is an associated anemia, not positively attributable to the strongyloides, but, on the other hand, not attributable to any other cause. It is possible that S. stercoralis may cause some degree of anemia in man. The amount is indeterminable in this region among hospital cases on account of the associated hookworm disease or malaria.
Portals of entry for various microörganisms are made by the female mother worm and her larvæ in the small intestine, and, while no case of general bacterial infection has been proved to have arisen in this way, its occurrence is possible and highly probable.
In the cultures of strongyloides of man, there is among natives, who presumably are infected with purely tropical strains, a very marked predominance of development by the indirect or sexually differentiated mode, in some cases, an absolutely pure culture of the indirect mode larvæ being obtained. There are, however, natives, cultures from whose stools contain from a single filariform larva of the direct phase up to a very definite predominance of this mode. Cultures from natives of the temperate zones contain a marked predominance of the direct phase larvæ.
The presence of the filariform (direct mode), larva is perhaps best accounted for by its being an attempt at more perfect parasitism (Stiles).
From a correlation of culture study with the results of a histological examination of the invaded mucosa, this explanation of the derivation of the two phases is suggested. The mother worm in the intestinal tract has two kinds of progeny: (a) those expelled into the crypts or lumen, and (b) those imbedded in the intestinal wall. One lot becomes larvæ of either the direct or indirect phase; the other lot of the opposite phase. It appears to me that the intraepithelial cell-developed larvæ furnish the direct phase, while the embryos expelled directly from the mother become the indirect phase larvæ.
This will require for its confirmation a study of cultures in connection with a histological examination of the infected intestinal wall.
Cold merely inhibits the development of the larvγaelig; into either the filariform (direct) or into the sexually differentiated adults, and does not alter the anlage.
The resistant as well as the infecting form is the filariform larva, and all chemical larvicides must be directed against this form. Thymol and an alkaline cresol resin soap were found to be effective larvicides for the filariform larvæ.
Two new strongyloides of the monkey and ant bear are described. Cultures of these nematodes show a predominance of the indirect mode of development.