Transmission-blocking effects of primaquine and methylene blue suggest P. falciparum gametocyte sterilisation rather than effects on sex ratio.

Gametocyte density and sex-ratio can predict the proportion of mosquitoes that become infected after feeding on blood of patients receiving non-gametocytocidal drugs. Because primaquine and methylene blue sterilize gametocytes before affecting their density and sex-ratio, mosquito feeding experiments are required to demonstrate their early transmission-blocking effects.