Effects of Temperature on Sporogonic Development of Plasmodium berghei

The effect of temperature on the sporogonic cycle of Plasmodium berghei was studied in two experimental mosquito vectors. Complete sporogonic development takes place in Anopheles quadrimaculatus at 16 to 21 C, and in A. stephensi at 16 to 24 C. The upper temperature limits for development appear to be the lowest reported for any plasmodia. The sporogonic development of P. berghei is apparently adapted to the narrow temperature range which is found in the microclimate of its natural vector. High temperatures have a more rapidly damaging effect on the early than on the late stages of sporogony. Mosquitoes exposed to 28 C for as short a time as 4 hr following their infective blood meal fail to develop sporozoites. If this high temperature treatment is withheld until the parasite completes the early stages of sporogonic development at a favorable temperature, exposure to at least 3 days of 28 C is necessary to induce visible damage. The mode of action of high temperature damage is unknown at present. Ever since the discovery of the rodent malarial parasite, Plasmodium berghei, by Vincke and Lips (1948), laboratory investigations involving the sporogonic stages of development of the parasite have been impeded by the inability to find a suitable experimental vector. Recent work (Yoeli, Most, and Bone, 1964; Vanderberg and Yoeli, 1965) has shown that the parasite can be readily transmitted by several species of anophelines if the infected mosquitoes are maintained at a temperature of about 21 C. This is the approximate daytime temperature that the natural vector, Anopheles dureni, is subjected to in its microclimate within the forest galleries of the Congo during the transmission season. Previous experiments conducted in our laboratory in which mosquitoes were kept at 28 C only rarely resulted in successful cyclical development. P. berghei, apparently, is unusual among the malarial parasites in that its sporogonic stages develop optimally at relatively low temperatures. After our initial success at cyclical transmission of P. berghei by experimentally infected mosquitoes, we thought it useful to examine in more critical detail the effects that Received for publication 1 December 1965. *This work, contribution number 36 from the Army Research Program on Malaria, was carried out under the sponsorship of the Commission on Malaria, Armed Forces Epidemiological Board, and supported in part by the U. S. Office of the Surgeon General, Department of the Army, and by research grant AI-02423 from the NIAID, NIH, U. S. Public Health Service. temperature has on the entire sporogonic cycle