Page:The Journal of Tropical Medicine, volume 6.djvu/238
THE JOURNAL OF TROPICAL MEDICINE. [July 1, 1908.
ae THE ‘I'serse Fry.
‘The discovery of a ‘trypanosome in sleeping sickness suggests.a very definite line of research with regard to the; etiology, epidemiology and prophylaxis of this fearful disease.
‘We know that trypanosoma infection may be con- tracted. either by direct contact (dourine), or through the intermediation of blood-sucking insects (nagana, surra, rat-trypanosomiasis). In dourine, or ‘ Maladie du Coit,” the disease is acquired, like syphilis, during sexual..congress. Schneider and Buffard produced dourine in a bitch by simply smearing the vulva with Fia. 8. blood’ containing Trypanosoma cquiperdum. Sub- sequently two dogs covered this bitch, and both con- tracted the disease in about a fortnight. Nagana and surra are spread by blood-sucking flies. Major Bruce” proved that Glossina morsitans is a carrier of nagana in Zululand, and Rogers“ found that a_ horse-fly (Tabanus)° disseminates surra in India. Trypanosoma Lewisi' is propagated amongst rats by the fleas peculiar to these rodents.
The former limitation of sleeping sickness to West Africa, the peculiar patchy distribution of the disease along ‘the large river valleys, its failure to spread in the’ West Indies; in South America, and in other coun- tries,’ though frequently imported with negro slaves, and thé’ possibility that, like nagana, it is caused by a trypanosome, suggest a fly of the genus Glossina as the carrier,
The genus Glossina comprises several species, some of Which ‘have a wide distribution in West Africa
The carrier of sleeping sickness should. be sought amongst the latter. Behn ahs
A most interesting and important point which, so far, has not been definitely ascertained is the manner in which the tsetse fly conveys nagana.
In South Africa, nagana has long been known to Kuropeans as “ fly disease.” In 1895 Major Bruce discovered that the tsetse flies are not venomous, but that, like the cattle-tick (Ripicephalus annulatus) im
Texas fever, they inoculate, with their bite, a deadly — protozoal organism. By infecting susceptible animals . in Ubombo with flies gathered in the low country
where nagana prevails, Major Bruce was able to prove that the Glossina
morsitans is a carrier of the distemper. Taking into consideration that an animal suffering from nagana does not communicate the disease to other animals in places devoid of tsetse flies, and that both the distribution of the disease and the distribu- tion of the fly show the same striking peculiarities, it may be reasonably surmised that other blood-sucking ecto- parasites are, as arule, un- able to convey the nagana flagellate. So far, very few experiments have been made to settle this point, and the various species of the genus Glossina have not been
tested.
Major Bruce states that Glossina morsitans carries the nagana parasites from affected to healthy animals much in the same way as the vaccinating needle carries the infection of vac- cinia from child to child. He further remarks that the fly is capable of inoculating living trypanosomes twelve, twenty-four and even forty- eight hours after having sucked the blood of an infected animal. I very much doubt that this can be the usual mode of transmission, If the tsetse fly acted merely in the way suggested by Major Bruce, it would be difficult to understand why the disease is not spread by other blood-sucking animals, such as mosquitoes, fleas and ticks, all of which are known to be capable
of transmitting blood parasites. Liely I am inclined to believe that Glossina morsitans is a
definitive host of Trypanosoma Brucei just like Anopheles costalis is a definitive host of Hamameba Laverani. Two important facts suggest this theory. First, the limita- tion of nagana to the so-called “ fly belts” ; secondly,, the probability of a double alternating cycle in the life-history of the trypanosome,
The probability of a dual life-cycle in trypanosomes _ is not only suggested by the analogy of other parasitic _
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