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Dr. Polidori had drawn up his official report with a map showing the southern limit of the endemic area. He describes it as commencing at Vua, on Tanganyika, and a line joining that to Mpweto and through Kiambi, Ankoro, Buli, Mwano-Kialo, Mutombo-Mapula and then westward to the Portuguese boundary, and that the disease is travelling slowly southward. Their experience points to Glossina Morsitans as well as Glossina Palpalis as a carrier of the disease.
At Mpweto there have been no cases at any time, but there are numerous cases at Baudouinville and Lusaka and everywhere further north.
Dr. Massey, Medical Officer of the Tanganyika Concessions at Ruwi, Congo Free State, sent some flies (Glossina Palpalis-Wellmani) to His Honour the Adminis- trator, North-Eastern Rhodesia, which were given to me. Dr. Massey wrote to the Lancet," August 4th, 1906, saying that this species had been found in two places: at the junction of the rivers Lufuka and Lualaba, about 10° 5' S., and at the junction of the rivers Dikulwe and Lufira, both in Katanga. He writes that isolated cases of sleeping sickness occur, but trustworthy evidence as to the locality in which the disease was contracted is wanting. Further enquiry is being made."
Dr. Todd, of Liverpool School of Tropical Medicine ("Lancet," July 7th, 1906), says, that before Europeans entered the Congo basin sleeping sickness was confined to the Lower Congo region and to the banks of the main river as far as Bumba (see maps). This was in 1884. In 1897 it was at Luluabourg and Lusambo,
on the caravan routes. It spread from Lusambo to Kasongo-a route much used by troops and caravans in the operations against the Arabs. From Kasongo to Baraka and Albertville, on Lake Tanganyika, are caravan routes for supply of region round Lake Kivu and Tanganyika north of 5° S. The route from Lusambo to Kasongo was closed in 1896, and supplies went up the Congo to Stanleyville and by canoes to Kasongo.
Sleeping sickness has spread along all these routes up and down the Congo from Kasongo, comparatively small stretches between Stanleyville and Kasongo being free. The map accompanying Dr. Todd's article is dated 1905. It will be observed that at Mpala and Baudoinville the cases were imported, and now endemic sleeping sickness exists.
The troops in the Congo are recruited and trained in infected areas around Boma, and are then sent to be stationed in different parts. The Vua case was a soldier; the Kasenga case is a soldier. These soldiers are trained to build, &c., and they teach, and have under them, local labourers.
III. SYSTEMATIC REVIEW OF THE CONGO AND NORTH-EASTERN RHODESIA BOUNDARY IN REFERENCE TO AN INVASION OF SLEEPING SICKNESS.
It will be convenient to begin at the Tanganyika end of the boundary. The lower limit of the endemic area in the Congo is stated to be at Vua. It is really, I think, further north at present, but will certainly reach Vua sooner or later, as the steamer once a month visits infected ports on the West Coast of Tan- ganyika, and the crew live in Vua 10 to 14 days every month while the boat is laid up, so that if any of them get infected up the coast, there is plenty of tsetse (Glossina Palpalis) in Vua to infect the whole place.
South of the Vua the conditions are different; fly is absent, roads are bad, and mountainous, and apparently very little traffic to the British side. I consider that the probability of direct extension to North-Eastern Rhodesia at this point is small. To the north of Lake Mweru, there are a considerable number of villages. At Kazembe, a village about midway between Mpweto and Chiengi is the junction of the Tanganyika Road. It is a native path. This road is more used by the natives than the Congo hoed road, as it is not so hilly. It joins the Congo hoed road between Ngakiro River and Kuntolwa, about 3 miles from each place. All round here, three hours from Kasembe, tsetse is very abundant, but whether this belt is continuous with the belt at Puta I was unable to ascertain. It is highly probable that this part will be infected early, by the direction marked by the arrows in the sketch map.
From Mpweto, to the mouth of the Luapula, which empties into Lake Mweru, is not dangerous, as there is no traffic across the lake.
• The term endemic is applied to those cases where the infection is derived from similar cases existing in the place and not.imported from other infected areas.
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From this point to Kaombi, there appears to be no danger, then there is a large population in the villages of Chilolo, Chiwunsi, Chongo, Chintori, Kisiwa, Mlundi, and in the case of the last two, there is a large amount of traffic with Kasenga where there is already a case of sleeping sickness. Fortunately, there is no йy on this side, and should cases arise, it seems unlikely that it will spread unless the disease is disseminated by other carriers than the tsetse (see below.)
From Mlundi to Madona, there is a sparse population on both sides of the river, and there is no traffic. At Madona is a point of the greatest danger. There is a continuous stream of natives to and from Kambove district about 150 miles away. Returning they are scattered all over North-Eastern Rhodesia, and if an infected case gets into or passes through one of the "fly" areas on this side, the result will probably be infection of the whole place. To the south of this is Chinyama, a place that appears to have been deserted as a ferry to the North-Western Rhodesia and Kambove mines in favour of Kapwepwe. There appears to be at the present time little or no danger in these places, nor in these parts along the river to Sakontwi.
IV. FACTORS OF THE DISEASE.
The Parasite.
It is stated in the recent reports of the Thompson, Yates, and Johnston Labora- tories, that the Trypanasoma Gambiense is the cause of the sleeping sickness; that those in Uganda and in Congo trypanosime fever are identical in every respect. That it has been inoculated into baboons, horses, cows, donkeys, sheep and goats, rats, guinea pigs, rabbits. &c., and that they are affected in a more or less chronic way, not necessarily fatal, and still remain virulent a year afterwards to susceptible animals; that there is periodicity in man and beast, and that the number of parasites bears no relation to the severity of the symptoms.
That it is incapable of attenuation by passing through a very resistant animal. Parasites passed through many hundreds of animals for three years still react.
The Carrier.
1. Glossina Palpalis and Glossina Palpalis Wellmani are known to carry disease.
It is probable that the other species of tsetse may do so.
2. Fleas. In the transmission of rat trypanosomes. Rabinowitsch has obtained positive results.
The Host.
Man is the one that concerns us most, but the parasite has been inoculated into other animals as hosts as mentioned above. Whether in nature they act as hosts there is apparently no proof, so that until that is forthcoming, it is necessary to consider them in methods of prevention as if they did so, although not so susceptible
as man.
It need only be mentioned that before the disease can exist the three factors must be present. In the absence of each one of these factors in turn the methods of dealing with the matter of dissemination will be modified accordingly.
There are four modes of arrangement of the factors that require consideration. These are as follows:-
Factors Present.
1. Host and fly ...
Factor Absent.
Parasite
Host
Indications for Action.
1. Remove host.
2. Remove fly (a) By cleared spaces.
(b) By destruction.
Removal or destruction of other hosts,
cattle, sheep, game, &c.
1. Removal of host (man) to area where
no fly,
3. Remove host to infeederisarea,
2. Fly and parasite
3. Host and parasite
Fly
2. Destruction of parasite by drugs.
4. Host and parasite and fly.
None
Remove host to where fly is absent.
Destroy parasite by drugs.
Host.-Man only is here considered as the host.