POTENTIAL EFFECT OF GLOBAL WARMING ON MOSQUITO-BORNE ARBOVIRUSES

If global warming curs in California, daily mean temperatures may incr ease by 3 to 5-degrees-C, precipitation patterns will change, and sea level may rise 1 m. Studies were done on effect of temperature changes on survival of Culex tarsalis Coquillett, the primary vector of weste rn equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) vir uses, in two regions where temperatures differed by 5-degrees-C. Daily mortality of adult vectors increased by 1% for each 1-degrees-C incre ase in temperature. At 25-degrees-C, only 5% of Cx. tarsalis survived for 8 or more days, the time required for extrinsic incubation of thes e viruses. Extrinsic incubation times for these viruses shortened when temperatures were increased from 18 to 25-degrees-C. WEE virus infect ion was modulated and transmission decreased at 32-degrees-C. If tempe ratures in the warmer region increase by 5-degrees-C, WEE virus may di sappear and SLE virus would persist. In the cooler region, a 5-degrees -C increase would decrease vector survivorship and virus activity in m idsummer. In North America, epidemics of WEE have prevailed above a 21 -degrees-C isotherm and those of SLE below this isotherm. With global warming, epidemics of these viruses could extend into currently unrece ptive northern areas. WEE virus would disappear from more southern reg ions. Geographic distribution of vector, human, and animal populations could be altered. North America could become more receptor to invasio n by tropical vectors and diseases.