Increased gametocytemia after treatment: An early parasitological indicator of emerging sulfadoxine-pyrimethamine resistance in falciparum malaria

Background. Although malaria treatment aims primarily to eliminate the asexual blood stages that cause illness, reducing the carriage of gametocytes is critical for limiting malaria transmission and the spread of resistance. Methods. Clinical and parasitological responses to the fixed-dose combination of sulfadoxine and pyrimethamine in patients with uncomplicated falciparum malaria were assessed biannually since implementation of this treatment policy in 1998 in Mpumalanga Province, South Africa. Results. Despite sustained cure rates of >90% (P = .14), the duration of gametocyte carriage increased from 3 to 22 weeks (per 1000 person-weeks) between 1998 and 2002 (P < .001). The dhfr and dhps mutations associated with sulfadoxine-pyrimethamine resistance were the most important drivers of the increased gametocytemia, although these mutations were not associated with increased pretreatment asexual parasite density or slower asexual parasite clearance times. The geometric mean gametocyte duration and area under the gametocyte density time curve (per 1000 person-weeks) were 7.0 weeks and 60.8 gametocytes/mu L per week, respectively, among patients with wild-type parasites, compared with 45.4 weeks (P = .016) and 1212 gametocytes/mu L per week (P = .014), respectively, among those with parasites containing 1-5 dhfr/dhps mutations. Conclusions. An increased duration and density of gametocyte carriage after sulfadoxine-pyrimethamine treatment was an early indicator of drug resistance. This increased gametocytemia among patients who have primary infections with drug-resistant Plasmodium falciparum fuels the spread of resistance even before treatment failure rates increase significantly.