Immunity to the sexual stages of Plasmodium falciparum in mothers, neonates and infants subject to intense and perennial malarial transmission.

The bloodmeal of a mosquito that has fed on an individual with a malarial infection may contain the parasites gametocytes as well as antibodies from the human. If antibodies against the sexual stages of the parasite are present these can prevent the fertilization of the gametes or further development of the sporogonic stages in the mosquito thereby preventing the transmission of the parasite to another human. Such transmission-blocking immunity (TBI) has been observed in sera from the inhabitants of malaria-endemic areas (Mendis et al. 1997) and has been correlated with responses to the principle sexual-stage antigens of Plasmodium falciparum - Pfs230 (Graves et al. 1988) and epitopes I and III of Pfs48/45 (Roeffen et al. 1995b). In maternal sera collected in Ifakara Tanzania - an area of intense and perennial malarial transmission - the levels of antibodies against the asexual stages of P. falciparum were found to correlate positively with those in the corresponding cord sera (Kitua et al. 1996). Maternally-acquired antibodies protected the children in this setting against symptomatic malaria for the first 4 months of their lives after which there was a significant decline in the titres of these antibodies and a tandem increase in malaria-related morbidity. It is not yet known whether antibodies to the sexual stages of the parasite are also transferred from mothers to their newborns and if so whether the levels of these antibodies follow a similar pattern of decline in infants. In the present pilot study therefore the presence and development of TBI during the first 12 months of life were explored in infants living in Ifakara. (excerpt)