Dengue (pronounced DEN-ghee) fever is caused by a virus spread by mosquitoes. It was formerly called "break-bone fever" because it causes excruciating pain to the muscles and joints of its human victims. Between 50 million and 100 million people worldwide get sick with Dengue fever each year, and about 5 percent of them die. No vaccine is available.
Most Americans are blissfully ignorant of Dengue fever because it is largely restricted to the tropics. But the mosquito species that spread the disease are moving northward and southward into temperate zones. One contributor to the expansion of Dengue fever is global warming, which allows the mosquito and virus to persist in areas that once were too cool.
Although Dengue fever marched northward through Mexico and many Caribbean islands in the late 20th century, the spread seems to have stopped at the United States border. But the Immigration and Naturalization Service can't take credit for keeping out this unwanted immigrant. Instead, it seems that Dengue fever's advancement into the U.S. was curtailed by our standard of living.
Most communities on our side of the border have good sewage and waste-water treatment, which reduces the number of nutrient-rich pools of water in which mosquitoes breed. American homes also tend to have window screens, air conditioners and various sources of entertainment (TVs, computers, etc.). These amenities keep people indoors, especially during evening hours when the mosquitoes are looking for someone to bite. So, at first glance, our relatively high standard of living seems to protect our citizens against some negative consequences of global warming.
But a recent study published in the journal Emerging Infectious Diseases should give us pause.
Researchers at the University of California, Davis, were concerned about an outbreak of West Nile virus - 140 confirmed human cases - in Bakersfield, Calif., in 2007. This outbreak was not expected. The main local body of water for breeding mosquitoes, the Kern River, had essentially dried up during a 2007 drought. The hot, dry weather that year had also reduced mosquito populations and several bird populations (West Nile virus proliferates in some birds). West Nile cases should have been fewer, not more, than usual.
What was going on?
The scientists undertook aerial reconnaissance over Bakersfield and were struck by the number of swimming pools and outdoor jacuzzis that were green instead of blue. Investigating further, they found numerous neglected, algae-infested pools creating perfect breeding grounds for the mosquitoes that transmit the West Nile virus. When they tried going door-to-door to question homeowners, they found entire neighborhoods virtually abandoned.
The downturn in the California housing market and skyrocketing adjustable mortgage rates had caused an unprecedented number of mortgage delinquencies. Properties were abandoned and swimming pools and jacuzzis were no longer treated with chemicals, resulting in a rich mosquito soup. The number of West Nile virus illnesses in the population that remained in their homes increased threefold.
One Threat Among Many
Tropical diseases are only one of many threats humans face as the planet continues to warm. Others include sea level rise that inundates low-lying cities, more intense hurricanes, and more frequent crop failures from droughts and floods. Moving forward, all human societies will benefit from actions that mitigate global warming. First and foremost, this involves investing in technologies and policies that reduce greenhouse gas emissions.
In the absence of these efforts, we will continually react to new climate-driven problems. While we are fortunate to have strong infrastructure, even developed nations such as the United States are vulnerable to market forces.
The ongoing economic downturn, and the rise of mosquito-rich swimming pools, is a reminder that our current ability to protect ourselves from the consequences of global warming is tenuous at best.