FIG. 4.

Evaluation of transmission-blocking activity by active immunization. Mice were immunized (prime and two boosts 4 weeks apart) with Pfs25-encoding plasmid or control (wild-type) plasmid. Mice were divided into three groups and infected with WT P. berghei, Pb28KO, or TrPfs25Pb and used to assess transmission to mosquitoes. Mosquito midguts were examined 10 days postfeeding. Data points represent mosquitoes that fed on three mice (Pfs25 DNA plasmid) or two mice (control DNA plasmid). Numbers on top of each data point indicate the percentage of mosquitoes infected (total number of mosquitoes dissected), and those next to horizontal lines indicate the mean number of oocysts. The reduction in oocysts of TrPfs25Pb parasites by vaccine-induced immunity was significant (P < 0.001; Wilcoxon test).