Effect of Temperature on the Vector Efficiency of Aedes aegypti for Dengue 2 Virus

Douglas M. WattsDepartment of Pathogenesis and Immunology, Disease Assessment Division, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, Maryland 21701-5011

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Donald S. BurkeDepartment of Virus Diseases, Walter Reed Army Institute of Research, Washington, DC 20012

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Bruce A. HarrisonWalter Reed Biosystematics Unit, NHB Stop 165, Smithsonian Institute, Washington, DC 20506

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Richard E. WhitmireUnited States Army Medical Research Unit-Kenya, Box 401, APO New York 09675

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Ananda NisalakDepartment of Virology, U.S. Army Medical Component, AFRIMS, Rajvithi Road, Bangkok 4, Thailand

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The effect of temperature on the ability of Aedes aegypti to transmit dengue (DEN) 2 virus to rhesus monkeys was assessed as a possible explanation for the seasonal variation in the incidence of dengue hemorrhagic fever in Bangkok, Thailand. In two laboratory experiments, a Bangkok strain of Ae. aegypti was allowed to feed upon viremic monkeys infected with DEN-2 virus. Blood-engorged mosquitoes were separated into two groups and retained at constant temperatures. Virus infection and transmission rates were determined for Ae. aegypti at intervals ranging from 4 to 7 days during a 25-day incubation period. Results of the first experiment for mosquitoes infected with a low dose of DEN-2 virus and maintained at 20, 24, 26, and 30°C, indicated that the infection rate ranged from 25% to 75% depending on the incubation period. However, DEN-2 virus was transmitted to monkeys only by Ae. aegypti retained at 30°C for 25 days. In the second experiment, the infection rate for Ae. aegypti that ingested a higher viral dose, and incubated at 26, 30, 32, and 35°C ranged from 67% to 95%. DEN-2 virus was transmitted to monkeys only by mosquitoes maintained at ≥30°C. The extrinsic incubation period was 12 days for mosquitoes at 30°C, and was reduced to 7 days for mosquitoes incubated at 32°C and 35°C. These results imply that temperature-induced variations in the vector efficiency of Ae. aegypti may be a significant determinant in the annual cyclic pattern of dengue hemorrhagic fever epidemics in Bangkok.

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