The chemotherapy of rodent malaria, XXXII. The influence of p-aminobenzoic acid on the transmission of Plasmodium yoelii and P. berghei by Anopheles stephensi.

More oocysts of Plasmodium yoelii developed in Anopheles stephensi if the mosquitoes received a supplement of p-aminobenzoic acid (PABA) in their diet prior to their taking an infective blood meal, than in unsupplemented control insects. The optimum concentration was 0.05% PABA in 10% sucrose. This effect was not observed if the blood meal was taken prior to feeding with PABA. Similarly, PABA administered to gametocyte-carrying mice increased the numbers of oocysts developing in mosquitoes fed on them subsequently, the effect also being dose dependent, and not mediated through an increase in gametocyte numbers. Sulphadoxine (which blocks PABA uptake) had the opposite action, reducing the numbers of oocysts either when fed directly to the mosquitoes or to the donor mice. These results are compared with those reported in other host-parasite systems by earlier workers, and certain paradoxical observations are discussed with reference to a possible relationship between sulphonamides and contaminating microorganisms in the vector mosquitoes.