Figure 6

Proposed relationship between male and female gametocyte clearance and transmission blocking effects in falciparum malaria. If male gametocytes are more sensitive to transmission-blocking drugs than female gametocytes, and female gametocytes predominate, then gametocyte clearance times are determined by the female gametocytaemia, and transmission-blocking effects are determined mainly by male gametocytaemia. In this illustration of gametocytaemia responses to drug treatment clearance half-lives are one day for male (blue) and two days for female gametocytes (pink). The limits of gametocyte detection by microscopy and Pfs25mRNA (which detects predominantly females) are shown by the dotted lines. If a density of >1,000/mL was required for mosquito infection, then in this illustration the maximum duration of possible infectivity is three days compared to a clearance time measured by Pfs25mRNA of seven days. In fact, drugs such as primaquine sterilize rapidly (Figure 7) suggesting that loss of infectivity precedes gametocyte clearance so the post-treatment duration of infectivity in this illustration is likely to be < one day.