The pattern of infectious diseases in Central Africa is determined by climatic conditions and socioeconomic factors. The climate in most parts is tropical, i.e., hot and humid. The region is dominated by the Congo River and its tributaries, and the area is covered mostly by savannah or primary and secondary tropical rainforests. Healthcare systems in some parts of Central Africa are disrupted, and there are many infectious diseases for which no data on prevalence and incidence are available. Prevalence data on these diseases can only be derived from single case reports or by analogy with other areas in Africa. Sao Tomé and Principe is an island nation in the Gulf of Guinea with a different disease spectrum, but tropical diseases like malaria, dengue, schistosomiasis, and lymphatic filariasis by Wuchereria bancrofti, and geohelminth infections do occur. No human cases of yellow fever have been reported, ciguatera fish poisoning is endemic.