Enhancement of a Simian Malarial Infection (Plasmodium Cynomolgi) in Mosquitoes Fed on Rhesus (Macaca Mulatta) Previously Infected with an Unrelated Malaria (Plasmodium Knowlesi) *

Abstract

Abstract A Plasmodium knowlesi infection in rhesus terminated by curative drug therapy and followed by a P. cynomolgi infection greatly increases the gametocyte infectivity of the latter species. Mosquitoes feeding on these rhesus show a 3-fold increase in oocyst number and a high percentage of mosquitoes become positive for the P. cynomolgi infection. Over a 10-day feeding schedule, mosquitoes which fed on experimental rhesus with previous exposure to P. knowlesi produced a mean oocyst count of 43.1 as compared to an oocyst count of 14.1 for mosquitoes feeding on control animals, with no prior exposure to P. knowlesi. An average of 83.6% of mosquitoes fed on experimental rhesus developed oocysts, while 53.3% of mosquitoes fed on control rhesus became positive after the blood meal. Daily average P. cynomolgi gametocytemias were low and varied only slightly between control and experimental animals, as did average daily parasitemias of both groups of rhesus. The time interval between the two malarial infections did not appear to be critical, at least not within the period from 4–20 weeks used in the present experiments. Results of in vitro feeding of mosquitoes on P. cynomolgi-infected blood through a baudruche membrane confirmed and extended those obtained from mosquitoes fed directly on rhesus.