Dengue in epidemic form has been a relatively uncommon disease in eastern Africa. In Zanzibar, epidemics have been reported at intervals since 1870 (GODDING, 1890) and have been reported more recently in Portuguese East Africa (DE SOUSA, 1924), in Madagascar (CuLLINAN, 1946), among troops in Ethiopia, Somalia, the Comoro Islands and Madagascar (MCCARTHY and WILSON, 1948), in the Belgian Congo (REuL and EERAERTS, 1949) and in Ethiopia (Bucco, 1950).

The epidemic to be described occurred on the Makonde Plateau in the Southern Province of Tanganyika. It was clinically indistinguishable from dengue, if allowance is made for the inherent variability of that disease. Dengue has not been reported from the area before and no inhabitant can remember a similar epidemic. Owing to the distinctive severity of the joint pains and the sudden onset a local name was rapidly applied; the disease became known as chikungunya, meaning-" that which bends up". An explosive outbreak of the disease was reported from several villages in October, 1952, but on detailed inquiry it became evident that a few villages had been infected during the previous months. The subsequent spread was rapid and it normally involved 60 to 80 per cent. of the population in each village within a period of 2 to 3 weeks of its starting there. In some groups of houses every inhabitant was infected. Sporadic cases would occur after the main invasion but these were usually modified and less severe in type. The spread appeared to be greater in the smaller units than in those larger settlements that had a better water supply. Towards its end the epidemic was not limited to the plateau but the spread round its base was slow and intermittent.