West Nile Virus
In the hour around sunset standing on my lanai looking south the sky is filled with birds and bats. Nighthawks, swifts and swallows swirl through the air collecting insects. I don’t like mosquitoes, but I’m sure that they provide a good diet to the birds.
Female mosquitoes need blood to produce their eggs and they get that from various vertebrates. Both the males and females also drink nectar and can even be helpful pollinators. Most of us are pretty fixated on the blood sucking part. I’d argue that they are better than vampires because vampires live forever and just drink blood so they can keep living their sick lifestyle. Mosquitoes only live a couple of weeks and they need the blood to propagate their species.
Unfortunately mosquitoes also transmit lots of diseases to humans: malaria, dengue fever, yellow fever, eastern equine encephalitis, and west nile virus. In this country the danger of these diseases is exceeded by the panic about them.
Our best weapons against west nile virus and eastern equine encephalitis is bug repellant and the elimination of stagnant water. When truly threatened localities spray a mixture of synthetic pyrethroids. I say synthetic because the original pyrethroids are derived from chrysanthemum family flowers.
Pyrethroids are broad spectrum: they kill all insects. They do this by opening the sodium channels in insect nerve cells. To avoid killing birds and butterflies, cities spray after dark when fewer insects are active and the birds are done feeding. They spray the equivalent of a teaspoon of active ingredient per football field sized area.
I have no doubt that other insects are killed. I also bet that some though not all mosquitoes are killed.
Dallas has recently decided to spray for mosquitoes because they’ve had 10 deaths this summer from west nile virus. I can imagine that seems terrifying. Suddenly you become deathly ill and die because a mosquito you didn’t even notice sucked your blood. I’m sure it affects the poor more than the middle and upper classes because in Dallas everyone who can afford it lives in an air condition cocoon.
But is this really a public health emergency? Dallas’ population is 1,223,000. The WNV death rate is therefore 1 per 122,000 people. How does that compare to other causes of death in Dallas?
Dallas is the tenth worst city to be a pedestrain in http://t4america.org/resources/dangerousbydesign2011/states/worst-metros/. Last year in the metro area there were 942 deaths. Probably we should spray for cars. According to the Kaiser family foundation there were 10.9 gun deaths per 100,000 people in Texas. There were 166 homicides in Dallas alone. Texas lost 17.5 people per 100,000 due to influenza and pneumonia. These are almost entirely preventable with appropriate health care choices.
Sure these are different problems, many of them more complicated. But the obsession with mosquito borne illnesses is misplaced: you are far more likely to get hit by a car, shot or die of the flu than you are to get WNV. Wear bug spray. And Texas, give people flu shots if you want to save lives.