Current developments in malaria transmission-blocking vaccines

Malaria is still a leading cause of morbidity and mortality in human popula tions. Problems, including drug-resistant parasites and insecticide resista nt mosquitoes, ensure the continued hold of malaria in the tropics and sub- tropics. Each year around 100 million cases of malaria result in at least 5 0,000 deaths outside of sub-Saharan Africa; within sub-Saharan Africa itsel f, malaria causes around one million child deaths per year. New approaches for malaria control are badly needed and much effort has gone to develop ma laria vaccines. In addition to giving personal protection, most such vaccin es would also tend to reduce the transmission of malaria. One class of vacc ine is being developed specifically for this purpose - the malaria transmis sion-blocking vaccines (TBV). TBVs are based upon antigens expressed on the surface of the sexual and mosquito mid-gut stages of malaria parasites. Th ese antigens are the targets of antibodies induced by vaccination of the ho st and ingested with the parasites in a mosquito blood meal. The antibodies act by inhibiting the parasite's development within the mosquito itself an d they thereby prevent the onward transmission of the parasites. TBVs could contribute to the total interruption of malaria transmission in many locat ions with relatively low transmission rates, mostly outside sub-Saharan Afr ica. Under almost all transmission rates, however, TBVs would help reduce m alaria incidence and malaria-related morbidity and mortality. Promising rec ombinant TBV candidate antigens for the two main human malaria parasite spe cies, Plasmodium falciparum and Plasmodium vivax, have been produced and te sted in the laboratory, one has undergone early clinical trials.