Further report on the tsetse fly disease or Nagana, in Zululand / by Surgeon-Major David Bruce.

  • Bruce, David, Sir, 1855-1931.
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: Further report on the tsetse fly disease or Nagana, in Zululand / by Surgeon-Major David Bruce. Source: Wellcome Collection.

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    4.—HISTORICAL ACCOUNT. In a fuller report it may be interesting to trace the history of this disease as it has occurred in Zululand during the last half century. How it has broken out in certain districts in certain years where it was before unknown, or disappeared in others where in previous years it had existed. Suffice it to say in this Report that the disease has evidently followed the laws of other infectious diseases, and spread some years to a greater extent than in others, when conditions favourable to it existed, or breaking out in epidemics and carrying off large numbers of domestic animals, where before only stray cases had occurred. The evidence, moreover, goes to show that the disease has existed in the lower tracts of the country time out of date, and is in no sense a new disease. 5.—ETIOLOGY. The opinions of the Europeans settled in Zululand and of the natives themselves are so conflicting that little or no good will be gained by entering fully into their evidence. Two theories are held. A. —That the disease is caused by the bite of the Tsetse Fly. Tins is the European theory, and as everyone knows has been popularly prevalent ever since white men first landed in South Africa. B. —That the disease is caused by the presence of large game, the wild animals in someway contaminating the grass or drinking water by their saliva or excretions. This may be called the native theory. A._THE TSETSE FLY. In this Report I think it well to begin with the consideration of the Fly itself, not only on account of its historical value, but also because I shall try to show that the Tsetse Fly plays a most important part in the propagation of the disease. Be it at once stated that I have not the slightest belief in the notion popularly prevalent up to the present that the fly causes the disease by the injection of a poison elaborated by itself, after the manner of a leech, which injects a fluid to prevent the coagulation of the blood, or the snake for the purpose of securing its prey or for defence, but that the Tsetse acts as a carrier of a living virus, an infinitely small parasite, from one animal to another, which entering into the blood stream of the animal bitten or pricked, there propagates and so gives rise to the disease. 1.—DESCRIPTION OF THE TSETSE FLY. As the question often arises when a fly has been caught as to whether it is the real Tsetse or not, I think it may he found useful for the purposes of this Report if I describe the fly, as known to me, somewhat fully, and give a few drawings of its. appearance. The Tsetse Fly, Glossina morsitans (Westwood), is about 11 mm. or seven-sixteenths of an inch in length. The head is buff coloured, darker on the summit, with two minute dark brown spots on either side, and is distinct from the thorax; the eyes are dark, the thorax is gray with a slight tinge of green, streaked longitudinally with brown, and covered with minute dark dots marking the site of short black hairs. The abdomen is pale yellowish-white or buff coloured, and consists of six segments, the central four of which have large oval shaped dark brown spots on either side of the middle line, giving the appearance of a narrow longitudinal yellow medium line, crossed by transverse yellow bands, of which four are well marked and one is indistinct. These yellow lines on the upper surface of the abdomen, the one down the centre, and the four crossing it, are as clear cat and distinct as if marked or drawn by a pen and ruler. The legs are buff coloured touched with yellow, and the tarsal hooks are bifid. The transparent wings are about 10 mm. long and 4 mm. broad and are smoky in colour. When the Tsetse is at rest the wings fold over one another like the blades of a pair of scissors, and give the fly an elongated appearance (Plate I. figs. 1 and 4). The Tsetse Fly does not lay eggs as do the majority of the Diptera, but extrudes a yellow coloured larva nearly as large as the abdomen of the mother. This larva is furnished with a black hood at one pole and two minute spikes at the other. It is annulated and consists of ten segments. Immediately on being born the larva creeps about with a good deal of activity, evidently searching for some cover or hole in which to hide. Having found a resting place it immediately begins to change colour, and after a few hours has turned into a jet black hard pupa.or nympha (Plate I, figs. 2 and 3). If these pupal cases are placed in a perfectly dry place, as in a wooden box. the perfect insect hatches out in about six weeks. From this it would appear that the life history of this species of fly is very simple, it only being necessary for the female