Review of some of the recent advances in tropical medicine, hygiene and veterinary science, with special reference to their possible bearing on medical, sanitary and veterinary work in the Anglo-Egyptian Sudan : being a supplement to the Third Report of the Wellcome Research Laboratories at the Gordon Memorial College Khartoum / by Andrew Balfour and R. G. Archibald.

  • Balfour, Andrew.
Date:
1908
Catalogue details

Licence: Attribution 4.0 International (CC BY 4.0)

Credit: Review of some of the recent advances in tropical medicine, hygiene and veterinary science, with special reference to their possible bearing on medical, sanitary and veterinary work in the Anglo-Egyptian Sudan : being a supplement to the Third Report of the Wellcome Research Laboratories at the Gordon Memorial College Khartoum / by Andrew Balfour and R. G. Archibald. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

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    Guinea He points out that these theories have become discredited, and gives further Worm— experimental and literary evidence in favour of their being discarded. The embryos cannot co7itinuccl infect man by the skin or mouth or undergo further development in water. His own observations on the vitality of the embryos in water show that the usual period of survival was three days, though some survived till the sixth day. In mud they lived a day or two longer, probably because in this medium they move more slowly and are consequently exhausted. Although provided with a mouth and digestive tract they are still unable to obtain food for themselves. ii. Those in which an intermediate host is considered essential for the development of the larva in order that it may become fitted to re-infect man. (d) The only, and in itself sufficient, host being cyclops. (e) A second, and at present unknown, intermediate host being necessary to continue and complete the changes begun in cyclops. Leiper, in his experiments in Nigeria, found that, of all the organisms in the ponds, cyclops alone was capable of infection, and he believes that the mode of entry of the embryo is not through the integument of the cyclops, as usually taught, but by way of the intestine. As regards the completion of metamorpliosis, he found that the striated cuticle of the embryo was cast generally on the eighth day. The larva which emerged lost, two days later, a very delicate enveloping pellicle, and from that time onwards underwent no further ecdysis. The subsequent changes were confined to the differentiation of internal structures, the larva apparently becoming mature in the fifth week. These observations differ from those hitherto accepted. Leiper also noted that the larvae showed no disposition to leave the cyclops and become free-swimming, evidence that infection of man does not occur by the skin. As time went on the larvae became more quiescent, and when the cyclops died the larvae were found dead in its interior. As regards the way in which they leave their host, Leiper^ refers to his previous work, in which he demonstrated the action of a 0-2 per cent, solution of hydrochloric acid in killing the cyclops and rousing the larvae to such activity that they speedily escaped by the mouth, anus, genital opening, or a breach in the cuticle of the cyclops, and swam about freely in the fluid. The later work has consisted in feeding a monkey on bananas containing cyclops which had been infected for five weeks, and which had in them apparently mature larvae. Six months later a careful post-mortem examination of the monkey revealed the presence in the connective tissues of five filariae, which possessed the anatomical characteristics of Filaria medinensis. There were three unimpregnated and obviously immature females about 30 mm. long, and two remarkably small males (22 mm.), which were obtained one from the psoas muscle and the other from the connective tissue behind the oesophagus. These results (says Leiper) point strongly to the truth of the theory that infection of man takes place from the drinking of water containing infected cyclops. The suggestion that a second intermediary host is necessary for the complete development of the guinea worm larva is disposed of by the fact that this is actually attained in cyclops. He comments upon the importance of the discovery of the male and immature female forms in the connective tissue, showing that the guinea worm thus comes into line with what we know of the after-development of other filariae. He thinks that Geotropism (tendency to grow downwards towards the earth) affords a rational explanation of the remarkable distribution of the parasite in man. An important fact to which attention is drawn is that the embryos are immediately killed if dried by natural evaporation, and they cannot be revived by the re-addition of water. A review is given of the conditions essential for the completion of the life-cycle of the parasite, as follows :— The young must be discharged directly into fresh water soon after the parent worm has succeeded in creating a break in the overlying skin and before the wound has become markedly septic. The embryos must find a cyclops within a few days. They must, moreover, succeed in entering its body cavity. Five weeks later they will have developed into mature larvae. These must, thereafter, be taken into the human stomach, and having been set free ' Leiper, R. T. (January 6th, 1906), The Influence of Acid on Guinea Worm Larvae encysted in Cyclops. British Medical, Journal, p. 19, Vol. I,