New Study: Climate Change To Help Spread West Nile Virus-Carrying Mosquitos



Longer, warmer, and wetter summers could bring mosquitoes carrying the West Nile virus to southern states for more of the year.

West Nile virus used to be a buzzword that had thousands of people petrified of going outside. A whiny buzz in the ear, a phantom itch on a calf — mosquitoes became more than just an annoyance. People were scared when the virus came to the U.S. in 1999, and it’s been a regular, if understated, part of the American summer ever since.

But a new study to be published this week in the Proceedings of the National Academy of Sciences (PNAS) sheds more light on how, where, and when exactly the virus could spread in the United States. Cory Morin and Andrew Comrie, researchers at the University of Arizona, developed a model that showed how climate change would affect the spread of the mosquito Culex quinquefasciatus, a known vector of the West Nile virus, across the southern U.S.

Morin and Comrie found that most areas will see a longer mosquito season as temperatures increase and summers get wetter and longer. The “good news” is that some southern states will see hotter and dryer summers — which may be bad for crops, water supplies, and public health, but it is also bad for mosquito larvae. Yet these states will see more months when mosquitoes can thrive on either end of a hotter and dryer summer. Northern states are less likely to get as severe heat and precipitation, yet those milder temperatures and adequate rain could help West Nile mosquitoes thrive throughout the summer.

This map from the PNAS study shows how the model predicts these mosquitoes will spread, and when. The maps on the right reflect most clearly how they will spread through the year. Red and yellow dots mean more mosquitoes, while blue ones mean fewer. The longer southern mosquito season can be seen clearly in March/April, May/June, and November/December.


The researchers suggested that public health workers need to look at responses to West Nile virus on a local scale to fully understand where and when it will spread.

It’s well known that this disease is exacerbated by climate change-fueled summers.

The summer of 2012 was the worst — the largest — outbreak in United States history. It killed 286 people, mostly in Texas, and the CDC reported a total of 5,674 cases in 48 states nationwide.

About 1 in 150 people bitten by a mosquito with West Nile Virus actually develop a severe illness. This involves flu-like symptoms, with aches and pains, but the virus can spread to the brain or spinal cord in some people, which is when it can be deadly, or cause paralysis.

So far, 2013 may not have been as blisteringly hot as 2012, but that does not mean climate impacts like the spread of West Nile have gone away. 20 people have died in 2013 from West Nile, with 497 cases reported as of September 3rd. 30 cases in Nebraska. At least 21 in Texas. 96 in Colorado. 23 in Mississippi.

On thing the University of Arizona study did make clear was that West Nile mosquito season will get longer, so those numbers could have more time to increase in 2013. Just eight states have taken measures to prepare to adapt to the public health impacts of climate change — and most of those are in the Norther U.S.