The coastal mountain ranges of Costa Rica had long confined dengue fever, a mosquito-borne disease accompanied by incapacitating bone pain, to the country's Pacific shore. But in 1995 temperatures allowed Aedes aegypti mosquitoes to breach the coastal barrier and invade the rest of the country. Dengue also advanced elsewhere in Latin America, reaching as far north as the Texas border. By September the epidemic had killed 4,000 of the 140,000 people infected. Of all the infectious diseases humans will have to contend with as the world gets warmer may be the worst.
Malaria is already the world's most widespread mosquito-borne illness.
Rising temperatures will not only expand the range of Anopheles mosquitoes, but make them more active biters as well. Paul Epstein, an epidemiologist with the Harvard School of Public Health , notes that a temperature rise of 2 C would more than double mosquito metabolism, forcing them more often. When temperatures rise above 40 C, mosquitos begin to die off-but at those temperatures, so do people and the crops on which they live. Humans often make matters worse for themselves by the changes they make in their local environments. Unusually warm waters played an important role in the cholera epidemic that hit Latin America in 1991, but the outbreak was also exacerbated by seawage poured into the waters off Asia and Latin America, the destruction of pollution-filtering mangroves in the Bay of Bengal and overcrowding in the cities.