The weather and West Nile: Let's stop arguing over climate change and fight the virus
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The United States is in the midst of its worst West Nile outbreak ever. A major factor influencing the spread of this mosquito-borne illness is the weather. Yet that very assertion has triggered a misguided debate about climate change when the focus should be on mitigating the spread of this deadly virus.
Weather's impact is clear. Warmer climates extend the geographic range of mosquitoes. Mild winters allow mosquitoes to repopulate more quickly in the spring. Higher temperatures make it so mosquitoes reach biting age sooner and speed up the multiplication of the virus inside of them. Humidity stimulates the mosquitoes to bite more.
Heavy rains produce ample breeding grounds. Mosquitoes even do well in a drought. Droughts can leave standing pools of water and nutrient-rich water in storm drains and catch basins, which allow the mosquitoes to thrive. After a drought, they repopulate quicker than other insects (including their predators) and therefore can have free reign.
Some claim that climate change is not occurring or, at most, that we are experiencing a normal cyclical increase in temperature. They have extended this line of reasoning to argue that climate change cannot be a factor in the West Nile outbreak.
This argument misses the point. Regardless of whether long-term climate change is culpable, temperatures are now on average much warmer than they were in the past and we are seeing more extreme weather events like heavy rainfall and droughts that enable mosquitoes to thrive. The public health consequences of these weather changes are the same whether we attribute them to global warming or cyclical weather patterns. The fact is that with milder winters, rainier springs and hotter summers, the United States will see an increase of mosquito-borne illnesses. West Nile virus is just one; others include malaria, dengue fever and yellow fever.
Over the past year, a large portion of the nation experienced a mild winter, which ushered in an early spring. Spring included unusually heavy rainfall followed by a summer of record heat and, in many locations, extreme drought. These conditions enabled mosquitoes to repopulate quickly and extended their biting season. They also caused birds to migrate to urban areas in search of water, bringing with them West Nile virus and the mosquitoes that spread it.
The weather is not the only factor influencing the spread of West Nile virus. Others include increases in the number of people in urban areas (where mosquitoes carrying West Nile tend to congregate) and poverty and poor social conditions that can stymie proper precautions being taken to prevent the disease from spreading (such as putting screens on windows and doors).
Nonetheless, it is foolish to discount the role of the weather in the spread of the disease. Understanding the influence of the weather on mosquito-borne diseases allows us to better plan for future outbreaks and to develop appropriate public policy responses.
For example, it allows us to have debates about the proper use of pesticides prior to emergencies, not during emergencies while people are dying and emotions are high. We need policy makers who are prepared to accept the fact that warmer weather patterns and extreme weather events influence the spread of mosquito-borne diseases and take necessary actions to protect the public from harm.
First Published August 30, 2012 12:00 am