Further reports (no. 4) on flies as carriers of infection.

Date:
1911
Catalogue details

Licence: In copyright

Credit: Further reports (no. 4) on flies as carriers of infection. Source: Wellcome Collection.

    18/52 (page 16)
    of parasites from faecal material to food. There are many flies, other than Musca domes tic a, which display like habits and though they do not bear such a close relationship to man several of them are commonly associated with the domesticated animals. With regard to their life-history the parasites of man may be divided into two classes, excluding the Filaria worms, and mention- ing only the best known species, as follows :— I. Those not requiring an intermediate host. a. Those in which the larval worm remains within the egg-shell. Ascaris lumbricoides. Toxascaris limbata. Belascaris mystax. Oxyuris vermicularis. Trichuris trichiurus. Hymenolepis nana. b. Those in which the larva is liberated from the egg- shell and spends its life in water. Ankylostoma duodenale. Necator americanus. Schistosomum haematobium. Schistosomum japonicum. II. Those requiring an intermediate host. a. Those encysting in animals which are commonly eaten by man. Trichinella spiralis in the pig. Taenia solium in the pig. Taenia saginata in the ox. Dibothriocephalus latus in fresh-water fishes. b. Those encysting in animals which may be swallowed accidentally by man. Fasciola hepatica in pond snails and eventually on grass. Dicrocoelium lanceatum in slugs and pond snails. Hymenolepis diminuta in fleas and other insects. Dipylidium caninum in fleas. There are several other common human parasites of which the life history is entirely unknown. Of those in the above list, the mode of infection of Schistosomum haematobium has not been defi- nitely proved, but it is probably similar to that of Schistosomum japonicum, the free-swimming larva of which is capable of infecting directly. Trichinella spiralis is peculiar in being viviparous and its larvae are shed into the blood stream or the lymphatics. The house-fly can therefore take no part in its dissemination. The species in II. b. are, as might be expected, but very occasional parasites of man. In addition to the above-mentioned worms of which man is the final or adult host, there are a few others for which man figures as the intermediate host. By far the most important of these is Taenia echinococcus, a tapeworm of the dog, the larva of which