Virulence of Plasmodium falciparum is associated with the expression of var
iant surface antigens designated PfEMP1 (P. falciparum erythrocyte membrane
protein 1) that are encoded by a family of var genes. Data presented show
that the transmission stages of P. falciparum also express PfEMP1 variants.
Virulence in this host-parasite system can be considered a variable outcom
e of optimizing the production of sexual transmission stages from the popul
ation of disease-inducing asexual stages. Immunity to PfEMP1 will contribut
e to the regulation of this trade-off by controlling the parasite populatio
n with potential to produce mature transmission stages.