Effect of xanthurenic acid on infectivity of Plasmodium falciparum to Anopheles stephensi

Terminally differentiated malarial gametocytes remain in the vertebrate cir culation in a developmentally arrested state until they are taken up by the mosquito. The gametocytes then undergo gametogenesis in the mosquito mid-g ut within minutes after ingestion of the infected blood meal. The male game togenesis (exflagellation) can be triggered by the combination of a decreas e in temperature of at least 5 degreesC and a simultaneous increase in pH b etween 8.0 and 8.3. Xanthureme acid, which is present in mosquito mid-gut a s well as in mosquito head, had been shown to induce exflagellation in vitr o at a non-permissible pH. Here we report for the first time that with the increasing concentration of exogeneous xanthurenic acid, there is a gradual increase in the number of oocysts in the mid-gut of infected mosquitoes. T he concentration of xanthurenic acid for optimum infection in the membrane feeding assay was determined to be 100 muM. Three different strains of Plas modium falciparum, viz. 3D7, 7G8 and W2 were tested in different experiment s and similar findings hold true for all of them. These results demonstrate that xanthurenic acid not only induces exflagellation of male gametocytes but also promotes infectivity of Plasmodium falciparum to mosquito vectors. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Sc ience Ltd. All rights reserved.