West Nile season begins

West Nile season is starting up, with the first few case reports trickling in.

Back in the summer of 2002, I was introduced to West Nile fever. This mosquito-borne viral illness had a minimal presence in North America in the preceding three years, but made its real American debut that summer. It may have hitchhiked over on boats or in an infected traveler, but either way, it's here to stay.

That summer, as I took over rounding on an inpatient medical service, I was suddenly faced with a relatively large number of very ill patients. They were usually elderly, and would be brought to the ER with fevers, headaches, low sodium levels, and confusion. More often than not, they developed weakness, often severe enough to land them in the ICU on a ventilator. Recovery was variable, with some people doing fine after rehabilitation, and others dying.

I went hiking in the woods that summer (with plenty of DEET solution) and saw a number of dead crows and blue jays, who also serve as unfortunate hosts to the virus.

There is no specific treatment for West Nile, but prevention involves mosquito control and avoidance.

There hasn't been another summer like '02. My state had over 600 cases in 2002, including 51 fatalities. Last year saw fewer than 20 cases. I've seen plenty of living blue jays so far.

Some of our success is due to vector control, but much is due to immunity. When the virus landed, very few Americans had been exposed. Now, many of us have, and our immune systems have been reasonably effective at mitigating the effects of this now wide-spread disease.

I still view mosquitoes differently. They never really bothered me, but after seeing so many horribly ill people, I think about those little pests before I go out in the evening.

West Nile is a beautiful model for emerging infectious diseases. I wonder what we'll see next?


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I'm a postdoc at the CDC. My thing is population genetics with some of the West Nile vectors, but here's a link that covers some DEET alternatives.


If you want to do something to cut down your chances of being infected in your own yard, empty standing water in your yard from things like flower pot saucers, and change the water in your bird bath frequently. Since the Culex mosquitoes are most active at dawn and dusk, put your repellent on especially then.

Actually having worked as a WNV technician, I can second LindaCO's comment about emptying containers.

Of all the cases I detected in mosquitoes, a huge proportion were from Culex. This is possibly due to a system of preferential sampling or the fact that they are a preferred vector (because they bite birds, which also leads to the preferential sampling), but also very likely due to the huge numbers of these mosquitoes that appear. They can nest in almost anything, and will with some zest.

If your yard or local environment has a large number of such environments, consider calling local mosquito control groups, often associated with county governments. They are helpful in many ways, often using safe larvasides such as Bacillus thuringiensis israelenis, or physically altering the environment by clearing blockage of water flow or old tires etc.

I would also like to add that WNV is largely under-reported, as the lesser cases appear just as the flu. Because of this, a lot of what comes to light is the worst of the worst.

Hey, I thought you were in the field?