PUBLIC RECORD OFFICE
Reference :-
| | 「 :། T T wui mului C.O. 885
22 PUBLIC RECORD OFFICE, LONDON
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and 15 wild mice, making a total of 698. The results were striking, a large propor- tion of the antelope being found to be infected with the parasites which cause As a conservative sleeping sickness in man and trypanosomiasis in domestic stock. estimate, the percentage of big game infected with the trypanosomes of man or domestic stock in the Lungwa Valley [may] be placed at 50, and at Ngoa, on the Congo-Zambesi watershed, at 35.
TABLE I.-Percentage of various species of game found infected with trypanosomes pathogenic to man or domestic stock in Nawalia, Luangwa Valley.
Bushbuck
Waterbuck
Kudu
Hartebeest
Roan Warthog Puku Mpala...
Animal
Number Examined.
Percentage harbouring Trypanosomes.
9
66.6
28
60.7
7
57.1
6
16.6
8
18-5
9
11.1
10 29
10.0
6.9 -
TABLE II.-Percentage of various species of game found infected with trypanosomes pathogenic to man or domestic stock at Ngoa, Congo-Zambesi watershed.
Sitatanga
Waterbuck
Eland...
Duiker Roan Puku...
Animal.
Number Examined.
Percentage harbouring Trypanosomes.
50 44.4
26.6
22.2
20
12.5
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This investigation, therefore, made it perfectly clear that the main reservoir of the trypanosomes of man and domestic stock is the big game.
Having ascertained these two essential facts, namely, that the tsetse fly, Glossina morsitans, is the vector by which the disease is spread, and that the big game is the inexhaustible reservoir of the virus which causes the disease, we are faced with the problem of what, in the light of this knowledge, can be done to stamp out sleeping sickness or to limit its spread in Nyasaland and Rhodesia. Obviously the most satisfactory means of prevention would be the extermination of Glossina morsitans, which conveys the parasite from one vertebrate host to another. Unfortunately, however, this is out of the question at the present stage of our knowledge. The only known method of getting rid of the fly from a district is by clearing away the bush. In the immediate vicinity of villages such a procedure is doubtless feasible, and would be attended by valuable results, and natives The labour should be encouraged to do everything possible in this direction.
involved in clearing large tracts of country would, however, be so great that this can be at once set aside as impracticable. Moreover, it must be remembered that not only would the country have to be cleared, but it would require to be kept cleared. Everyone who has had experience of tropical Africa is familiar with the dense shrub growth which springs up in the site of old garden clearings, two or three years after the natives have ceased cultivating the land. This shrub growth is exceedingly favourable to Glossina morsitans, so that unless the country be constantly kept cleared the last state of the district is worse than the first.
At present but little is known of the bionomics of Glossina morsitans. The results of investigations carried out up to the present indicate that this tsetse fly has no particular breeding places, but that its pupæ are deposited in a more or less haphazard manner in hollow trees and excavations where they are not likely to be disturbed by game birds. Regarding the liability of the fly to disease and of its natural enemies we know nothing. Much more information is required on this subject, but it seems only too obvious that the investigations will be beset by great difficulties, and that the information will only be forthcoming as the result of much
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slow and tedious work. In fact, to those familiar with morsitans country the exter- mination of the fly must seem an almost impossible procedure.
In Uganda, where the disease is spread by Glossina palpalis, the removal of the population a short distance away from the lake shores and water-courses was followed by most excellent results. Such a measure, however, is impossible in Nyasaland and Rhodesia, where the vector, Glossina morsitans, is practically ubiquitous in its distribution and not limited to water-courses, as is Glossina palpalis.
In view of the impossibility of exterminating the fly, and of the equal impossi- bility of removing the population from the fly belts, we must consider the only way that remains of combating the disease, that is the advisability of attempting to destroy the reservoir of the virus. It is obvious that the mere isolation of infected human beings is futile, in view of the fact that the main reservoir of the virus is the blood of the big game.
And now we come to a subject to which I particularly wish to draw your attention a subject which has excited considerable controversy already, and one which will, I expect, excite still more in the near future. I refer to the connection between big game on the one hand and trypanosomiasis of man and domestic stock on the other.
Since the beginning of last year, when Dr. Kinghorn and I published our paper announcing the fact that a large proportion of the wild fauna of Africa harboured the trypanosomes of man and domestic stock, a considerable polemic has arisen over the question of the advisability of attempting to exterminate the big game in the vicinity of human habitations.
the
In discussing this subject it appears to me that I could not do better than attempt to answer some of the objections which have been raised against any prophy- lactic measure being adopted which involves interference with the African fauna.
It has been suggested that if the big game be destroyed in any district, then the fly, being deprived of its natural source of food, might turn its attention solely to man and his flocks and herds. It appears to me that but little importance should be attached to this hypothesis. In the first place cattle do not as a rule live in presence of Glossina morsitans. It was suggested that cattle and other domestic stock might harbour the human trypanosome for considerable periods without detri- ment to health. This, however, is not true in the case of the human trypanosome of Nyasaland and Rhodesia, which we proved rapidly killed horses, cattle, donkeys, goats, and dogs. Moreover, even if the human parasite did not kill domestic stock, these would still die from the ordinary cattle trypanosomes, such as T. pecorum, T. nanum, and T. vivax, with which we found the wild Glossina morsitans to be heavily infected; so that it is quite obvious that domestic stock cannot have the same significance, as a reservoir of the virus, as the antelope, which are tolerant of the trypanosomes pathogenic for man and domestic stock. Secondly, the tsetse fly does not invade the clearings in and around villages to any great extent, and therefore man is only attacked when for any reason he goes forth into the bush, and it is hard to believe that he would suffer to any much greater extent in the absence of game. Thirdly, and this is the most important point, if the game were removed the reservoir of the virus is destroyed, and, therefore, in a short time the fly would tend to become non-infective. The bite of a non-infective Glossina morsitans hurts nobody. Finally, there is absolutely no evidence indicating that if the big game in any particular district were slaughtered the tsetse fly, unable to obtain blood from these animals, would attack man and the domestic animals to a greater extent that at present. It might equally well be argued that if the food supply of the fly be removed the fly would disappear. There is, moreover, a considerable amount of evidence that the tsetse fly spreads with the game. example, since the rinderpest swept through Central and South Africa sixteen or seventeen years ago, the big game has increased enormously in numbers, and with this increase in game there has been a corresponding increase in the number of tsetse fly. At Nawalia, in the Luangwa Valley, where we were stationed, Glossina morsitans was present in enormous numbers, and natives sent out to collect the flies had no difficulty in capturing large numbers within a short distance of the laboratory. Nawalia is the site of an old Government Station which was closed a few years ago on account of sleeping sickness. The magistrate who was stationed there in 1905 told me that he only occasionally saw tsetse flies in this district at that time.
For
Again, it has been suggested that the big game might be only one of the reservoirs of the disease, and that the infection might equally well be conveyed by the small