CONFIRMATION THAT PLASMODIUM-FALCIPARUM HAS APERIODIC INFECTIVITY TO ANOPHELES-GAMBIAE

In preparation for field studies of transmission-blocking malaria vacc ines, a study was carried out to determine whether P. falciparum infec tions obtained in An.gambiae blood-fed at 16.00 hours were quantitativ ely similar to infections obtained at 23.00 hours. Using a group of ch ildren aged 5-12 years from villages at Ahero, near Kisumu in Kenya, 7 1/74 (96%) of whom were found to be positive for P.falciparum parasita emia, one batch of fifty colony-bred An.gambiae females were fed on vo lunteers at 16.00 hours and another batch at 23.00 hours. No statistic ally significant differences were found in the proportions of mosquito es becoming infected, the numbers of children infecting mosquitoes or the mean numbers of malaria oocysts developing in mosquitoes blood-fed at the different times. Because mosquito infections obtained by day ( 16.00 hours) are equivalent in quantity to those obtained at night (23 .00 hours), experimental infections can be carried out in the afternoo n, when it is most convenient, rather than during the night.