Because both diseases are prevalent in tropical and sub-tropical regions, they overlap geographically and there is a persistent danger of co-morbidity, particularly in malaria endemic regions with large HIV-positive populations, such as sub-Saharan Africa. Co-morbidity is promoted by the tendency of both diseases to disproportionately affect the poorest communities, reflecting the lack of education, nutrition, information, prophylactics (e.g. malaria nets, condoms) and effective drugs.