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The Influence of Temperature on Plasmodium Vivax

1. The sporogenous cycle of P. vivax in A. quadrimaculatus was completed within the temperature range of 15–17°C. to 30°C.

2. The shortest time in which the cycle was completed in the insect vector was 8 days after the infective feeding; the longest period was 38 days.

3. The optimum temperature for the development of the exogenous cycle of P. vivax was 28°C., the lowest temperature at which the cycle was completed in the shortest time.

4. In all stages of the exogenous cycle, P. vivax was more susceptible to unfavorably high temperatures than to unfavorably low temperatures.

5. Shortly after feeding on a gametocyte carrier A. quadrimaculatus was completely sterilized of its plasmodial infection at 37.5°C. in 2 to 3 hours; at temperatures of 1 to 10°C. 2 days were necessary. During the growth of the oocysts (7 to 13 days after the infective feeding) exposure of the mosquito to 37.5°C. for 18 to 24 hours aborted its development, only a very small percentage of these mosquitoes ultimately showing sporozoites in their salivary glands. At 1 to 10°C., 24 days were required to interrupt oocyst development. When the sporogenous cycle was completed and sporozoites were present in the salivary glands of the anophelines, 24 hours' exposure to 37.5°C. had a marked inhibitory effect on the infectivity of the sporozoites in human inoculation. This effect was not observed in anophelines kept at 1 to 7°C. until after 50 days at this low temperature.

6. The developmental forms of the malaria parasite present shortly after feeding were most susceptible to unfavorably high and low temperatures; the sporozoite was least suceptible to unfavorable temperatures; the oocyst occupied an intermediate position.

7. Anophelines which developed their malarial infection when incubated at the lowest or at the highest temperatures possible for the completion of the exogenous cycle were infective.

8. The fact that P. vivax will not develop at constant temperatures above 30°C. and the fact that a period of 24 hours at 37.5°C. will sterilize all but a very small per cent of A. quadrimaculatus of their P. vivax infection have a bearing on the transmission of P. vivax infection during the summer months. The data presented show that in certain localities the oocyst may survive the winter and complete its development the following spring.

9. The adult Anopheles quadrimaculatus will survive higher and lower temperatures than the developmental forms of the malaria parasite which infect this insect.

Received January 29, 1940.