Pyretophorus costalis, a malaria carrier

Stegomyia fasciata, the yellow fever mosquito

16 MOSQUITO WORK IN KHARTOUM, ETC.

For all that, the presence of Culex fatigans was not felt to be very alarming, but it was a different matter when Pyretophorus costalis was encountered. This species of the Anophelina has been proved to be both a filaria and malaria carrier, and though it did not exist in great numbers had yet to be seriously reckoned with, even although Khartoum and its neighbourhood cannot be called

a malarious district. This is simply because the Anophelines cannot find many suitable spots wherein to breed—the result of a small and limited rainfall, the comparative absence of vegetation and the power of the sun’s rays as an evaporating agent. Still, as long as Pyretophorus costalis persists in Khartoum there will be a risk of malaria being spread from person to person. As already stated birds of passage are common in the town, and many of these come directly from the malaria-ridden reaches of the Blue and White Niles, while a greater number hail from Egypt, where malaria certainly occurs. In the bloods of different patients in

Khartoum I have found all three forms of the malaria parasite, i.e., quartan, benign tertian, and sub-tertian or malignant. The two latter forms are the most common, and the small ringed form and crescent forms are frequent in patients coming from up the White Nile. Now Khartoum is a garrison town, and probably the majority of the Sudanese soldiers at least have served or lived in malarious districts and have acquired the parasite. The same is true of their Egyptian comrades-in-arms, who are exceedingly susceptible to infection and suffer severely. I believe that one reason why there has not been more malaria in Khartoum is to be found in the fact that the military hospital is at present situated far from the breeding grounds of the Anopheline, which would have to cross a bare stretch of wind-swept desert, over a quarter of a mile in breadth, to reach those who might transfer to it the protozoon.

Nor must it be forgotten that many members of the crews of the steamers plying on both Niles harbour crescents in their bloods, and are constantly exposed to infection during their journeys in the south. It is not infrequent for several members of a steamer’s company to arrive in Khartoum prostrated by fever, and such patients may well prove centres of distribution.

Pyretophorus costalis is the only representative of the Anophelina which has been discovered in Khartoum, but a third genus of mosquito occurs which in point of numbers comes midway between Culex fatigans and Pyretophorus costalis, being nothing like so common as the former but considerably in excess of the latter. This is a Stegomyia, species fasciata, which in the western hemisphere has been proved beyond all doubt to be the active agent in the dissemination of yellow fever. Here the germ of that disease does not, so far, exist to be transferred by it, but the Stegomyia is the most troublesome insect of the three, being exceedingly lively and biting viciously even in the heat of the day. As will be shewn Stegomyia also breeds in Khartoum, though not to any great extent. Its prevalence is, I believe, to be attributed to the presence of so many steamers on the Blue Nile for Stegomyia fasciata, as has often been pointed out, is an excellent traveller. Along with Culex fatigans it has been found breeding in large numbers in the bilge-water, tank-water,

and engine-room-water of the river steamers.