The effects of subcurative doses of chloroquine on Plasmodium vinckei petteri gametocytes and on their infectivity to mosquitoes

Abstract The effects of subcurative doses of chloroquine on rodent and human Plasmodium transmission to the mosquito have been studied by several authors who showed a short-term (12 h) enhancement of gametocyte infectivity by the drug, restricted to chloroquine-resistant strains, and a long term (4–6 days) enhancement of gametocytogenesis of chloroquine-sensitive strains of Plasmodium chabaudi. We investigated both short- and long-term effects of chloroquine on Plasmodium vinckei petteri , a chloroquine-sensitive rodent Plasmodium strain. Chloroquine treatment reduced the index of gametocytogenesis to 73% (5 mg/kg) and 55% (2.5 mg/kg) of controls, on day 6 post-infection (p.i.). The reduction was statistically significant with 5 mg/kg chloroquine. However, the reduction of gametocyte numbers did not affect the transmission capabilities of the strain. Our experiments showed that doses of 1 mg/kg chloroquine had no effect on the oocyst counts, 12 h post-administration to mice. A statistically non-significant 61% reduction of oocyst numbers was observed in mosquitoes fed on mice treated with 5 mg/kg chloroquine. The effect of 5 mg/kg chloroquine administration on the infectivity of gametocytes to mosquitoes fed 1 h post-treatment was also investigated. An overall 41% reduction of oocyst numbers was observed. This immediate effect was statistically significant in 73% of the mice. These results are consistent with the hypothesis that the short-term enhancing effect of chloroquine on transmission is restricted to the drug-resistant strains of Plasmodium .