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.

    15/52 (page 13)
    3.—On the Part Played by Flies in the Dispersal of the Eggs of Parasitic Worms. By William Nicoll, M.A., D.Sc., M.B., F.Z.S., Ernest Hart Memorial Scholar of the British Medical Association (from the Lister Institute of Preventive Medicine, London). The somewhat scanty literature bearing on this subject has been summarised by Nuttall (1899), Nuttall and Jepson (1909), Hewitt (1909), and most recently by Galli-Valerio (1910). The greater part of it deals only with vague surmises, unsupported by actual observation or experiment. The only experimental observations which have hitherto been made are those by Grassi (1883), Stiles (1889), Galli-Valerio (1905), Calandruccio (1906), and Leon (1908). It was early recognised that the house-fly is an insect with a penchant for visiting excremental matters for the purpose both of feeding and breeding. The fact, too, did not escape observation that the body and legs of the fly, by reason of their numerous bristles, are peculiarly adapted for carrying any debris which might adhere to them. It was a natural suggestion, therefore, that the eggs of parasitic worms, deposited in excrement, might adhere to flies and so be transported by them from place to place. A more secure and certain means of transport, however, was pointed out by Grassi, who demonstrated that flies could actually ingest the eggs of parasitic worms and carry them in this way for a considerable distance. He further showed that such eggs, when ingested by a fly, could pass through its intestine and be deposited in its faeces, apparently unaltered and undamaged. To this experiment Calan- druccio has added an important observation showing that the eggs, after their passage through the fly, remained infective. A number of flies which had fed on infective material containing the eggs of a tapeworm (Hymenolepis nana) subsequently deposited a few of those eggs on sugar. A girl who had eaten some of this sugar was found twenty-seven days later to be infected with the tapeworm. The parasite is a very common one in southern Italy, but in this particular instance infection through other sources was carefully excluded, so that the observation appears to be perfectly trustworthy. The observations of Galli-Valerio relate to the American hook- worm (.Necator americanus). (In his earlier paper he says Anhylos- toma duodenale.) He found that flies could carry on the surface of their body not only the eggs but also the larvae of this dangerous parasite. Neither eggs nor larvae were found in the intestine of the flies. Leon’s experiment consisted in feeding flies on honey, with which were mixed the eggs of the tapeworm, Dibothriocephahis latus. He was able to recover the eggs from the excrement of the flies. These comprise all the actual observations which have, so far, been published on this subject. The result of an experiment of a some- what different nature was mentioned by Stiles in a personal com- munication to Nuttall. He allowed fly-larvge to feed on egg-bearing female round-worms (Ascaris lumbricoides). On examining some of