— 55 — Malaria.

In the report for 1927 attention was drawn to the fact that anopheline infec¬ tions had been very markedly in excess of culex infections during the months of October and November and that an increased malaria incidence was likely to follow during the winter months. Fresh infections of malaria in Khartoum began to be reported in December and these were followed during the months of January, February and March by a small epidemic in the three towns. In the Rural District, which is much less under our control, it is probable that about 70 per cent, of the population suffered from new infections or relapses during these months. As will be seen from the tables, the total number of new infections notified in the three towns during the year was—Khartoum 155, Khartoum North 111, Omdurman 31, total 297. These were the highest figures recorded during the past five years, but were in no way comparable to the figures for the two years of 1922 and 1923 when the figures recorded reached 1,071 and 1,576 respectively.

Observations recently published on the epidemiology of malaria in certain parts of India shew that epidemics tend to occur at five yearly intervals and are dependent amongst other things on an optimum temperature and relative humidity following on an increased rainfall and a lowered resistance of the population.

It is interesting to note that all these points were clearly demonstrated in Khartoum Province during the months of August 1927 and April 1928 ; i.e. it was five years since the previous epidemic of 1923, the rainfall was the highest record¬ ed since 1923, the temperatures and relative humidity were higher for these months than the previous year and approximated more to those recorded in 1922 and 1923 and the resistance of the population other than Europeans had been lowered by four years of very poor rains and corresponding high price of staple foods. The previous epidemic to that of 1923 occurred in 1918 and provides further evidence of the five yearly interval for epidemics of malaria in Khartoum Province.

There is also evidence which sho ws that there is a tendency for tw'o consecu¬ tive years to have a higher malarial incidence, thus in the years 1917 and 1922 there were malarial epidemics which reached their peaks in the following years. If there is anything in this observation is would appear to predict an increased incidence of malaria during the year 1929 ; up to the time of writing (end of February, 1929) this has not been the case although the anopheline infections found in river pools have been far higher than in 1928, but the intensive campaign against mosquitoes has not permitted any large breed out of adults. It remains to be seen whether conditions will be favourable during the coming rainy season and if so whether they can be adequately dealt with.

Adult mosquitoes were not markedly in evidence during the winter months, which means that they were not locally bred out, but rather that a few heavily infected mosquitoes were brought into the towns from outside, more particularly along the river front of Khartoum as evidenced by the distribution of the cases.

During the rainy months of August and September numbers of mosquitoes were brought into the town by the railway trains arriving from the south, particu¬ larly from Makwar. No less than six different species were obtained in and around the railway station and in various parts of the town. A routine inspection and disinfection of trains was begun in September and a visit was paid to Wad Medani and Makwar in order to arrange for a closer inspection of railway carriages at these points. It must be recorded that the measures taken by the authorities at Makwar had an almost immediate effect on the importation of mosquitoes into Khartoum and by the beginning of October it was rare to find any mosquito on trains from Makwar.