No Link Found between Global Warming and Mosquito-borne Diseases

Published September 1, 1998

The popular belief that mosquito-borne diseases–chief among them malaria, dengue, and yellow fever–will spread if global temperatures start to rise ignores both science and history, an infectious-disease expert told a briefing for Congressional staffers.

Paul Reiter, chief of entomology at the Centers for Disease Control and Prevention (CDC), pointed out that the mere presence of mosquitos that can transmit a disease does not guarantee the transmission will take place. While malaria, dengue, and yellow fever continue to plague many lesser-developed nations, they have all but disappeared from the United States and Europe, where they were once quite prevalent. Reiter noted that normal summer temperatures in parts of the United States are considerably higher than in the tropics where these dread diseases are still quite common.

The draining of wetlands, mosquito screens, air conditioning and central heating, vaccination (against yellow fever), disease therapy (anti-malarial drugs), and vector control (spraying for mosquitos) have all but eradicated the mosquito-borne disease from the U.S. and Europe. Even if global temperatures were to rise, Reiter observed, the U.S. and Europe would be safeguarded by the same factors that protect them today.

Just how crucial economic development can be in preventing the spread of such diseases was readily apparent in 1995, when an outbreak of dengue–a mosquito-borne viral disease closely related to yellow fever–swept up to the border between Mexico and Texas. Nearly 6,000 cases of dengue were reported in Tamaulipas, a low-income, under-developed Mexican state on the Texas border; only seven cases were reported in the entire state of Texas.

Temperature is also not the determining factor in incidences of malaria, explained Reiter. Contrary to popular belief, malaria is not a tropical disease; it has been known to strike as far north as Canada, Scandinavia, and northern Russia. And in tropical areas where vector control and anti-malarial drugs are unavailable or rarely used, malaria runs rampant.

Yellow fever was a major cause of death in the U.S. and Europe until shortly after the turn of the century. It is still present in Africa and South America, where it is transmitted by the Aedes aegypti. That mosquito species, Reiter pointed out, can be found throughout the southeastern United States; nevertheless, yellow fever here is little more than an unpleasant memory.

Regrettably, EPA continues to trumpet the alleged link between climate change and mosquito-borne illnesses. The agency’s global warming Web site contends that “the geographic range and life-cycles of pathogens and vectors (e.g. mosquitos) which transmit disease are affected by climate. Climate change would, in aggregate, increase the transmission of vector-borne diseases.”

Reiter, who has spent his career traveling the world investigating mosquito-transmitted diseases, told Congressional staffers that too much attention was being diverted from the important task of controlling and preventing diseases, and too much time spent “blaming it on the weather.”

The July 28 briefing was sponsored by the Cooler Heads Coalition, a group of 23 non-profit organizations concerned with the affects of global warming policies on consumers.