Scientists using computers to simulate the general circulation of the earth's climate have predicted that rising global temperatures will increase the potential transmission of the dengue fever virus. Dengue fever is now considered the most widespread viral infection transmitted in man by insects, whether measured in terms of the number of human infections or the number of deaths.
Their report appeared in the March 1998 issue of Environmental Health Perspectives, the monthly journal of the National Institute of Environmental Health Sciences.
Most of the new areas of increased potential risk were predicted to be temperate regions that currently border on endemic zones. These fringe areas represent places where humans and the primary carrier, the mosquito Aedes aegypti, often co-exist, but where lower temperatures now limit disease transmission. Lead author Jonathan Patz, MD, MPH, from the Johns Hopkins School of Public Health said, "Since inhabitants of these border regions would lack immunity from past exposures, dengue fever transmission among these new populations could be extensive." Unlike the yellow fever virus, carried by the same mosquito, the dengue virus is not vulnerable to any vaccine or drug. Major epidemics of dengue have occurred in the southeast United States, the largest in Galveston, Texas, in 1922, when over 500,000 people were stricken. The last outbreak in Texas occurred as recently as 1995, during an unseasonably hot year.
The researchers used three different general circulation models to predict the patterns of global climate change; all three showed that dengue's epidemic potential increases with a relatively small temperature rise. The higher a virus's epidemic potential, the fewer mosquitoes are necessary to maintain or spread dengue in a vulnerable population.
The geographic range of Ae. aegypti is limited by freezing temperatures
that kill overwintering larvae and eggs, so that
Contact: Sharon Rippey
Johns Hopkins University Bloomberg School of Public Health