CDC Offers Weak Numbers on West Nile Spraying

Before we blanket ourselves with pesticides, we should clear some things up.

In the treatment of non-neuroinvasive disease in the report, Boyd sees troubling evidence of a "circularity" he thinks is evident in another important part of the report dealing with mosquito populations. This one is a major sticking point for critics of the report. Helmick-Richardson told me he was "appalled" it was not even mentioned in the Morning News story by Sherry Jacobson.

"Did she even read the report?" he wondered.

Because the spray campaign here was carried out at a time when West Nile infection rates were already plummeting as part of the natural cycle of the disease, all of the areas covered by the report, sprayed and non-sprayed, showed dramatic declines in infection. That made a tricky statistical business of attributing degrees of decline to the spray.

Jared Boggess


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But if the spray was effectively killing mosquitoes, it should not have been difficult to measure declines in mosquito population. Indeed, right after the spray campaign here last year CDC experts endorsed a preliminary report claiming a 93 percent kill rate for mosquitoes.

The shocker in this new report was that after a closer look the CDC had to back away from the 93 percent kill-rate claim. Far far away. In fact the final report found that mosquito populations in sprayed areas actually increased slightly during the spraying.

The CDC report seeks to minimize this fact with a kind of off-the-cuff theory that the increase wasn't a threat to anyone. This is where Boyd finds his second "circularity."

The report states there were "small but statistically significant increases in mosquito abundance." But it suggests that new mosquitoes were not a problem, because they hadn't had time to bite any infected people or birds and become carriers.

But later the report states that blood-fed mature mosquitoes, the ones that could be carriers, are the ones most likely to escape the effect of the spray. Why, Boyd wonders, would that not make the blood-fed disease carriers more numerous than the newly emergent mosquitoes in the rising overall population of mosquitoes?

"It's a circular argument," he says. "Very, very contradictory."

But why would the CDC have any agenda here other than science? If the critics are right and they've got a thumb on the scale, what would be their motivation?

Some experts, even those far from us, have taken special note of the early appearance and ongoing role in Dallas last year of the CDC as aggressive champions of aerial spraying. David Pimentel, an emeritus professor of entomology at Cornell University and an expert on mosquito control, told me he was surprised to learn the CDC was in Dallas pushing aerial spraying because in the past it has always thrown its weight behind what he called safer and more effective methods of mosquito control.

Pimentel, who was on the staff of the CDC at one point in his career, said that before Dallas, the CDC always has recommended that communities hand-spray places where mosquitoes breed more than relying on airplanes. "They recommended in their publications anyway that you go after the larvae and pupae, and I agree with them that this is an effective means because you don't have to worry about the wind and so on. It's safer and more effective."

In looking for evidence of a biased advocacy for spraying in this new report, both Boyd and Helmick-Richardson point to another aspect of the report not even mentioned in the Morning News story — the margin of error. According to the report, the CDC actually is not sure whether infection rates decreased six times faster in sprayed areas than non-sprayed or decreased at the same rate. If it's the same rate, then the spraying had no effect at all on infection rates.

To be sure of this, I asked the authors of the report if the lower parameter in their margin of error meant infection rates in sprayed areas and in non-sprayed areas may have been the same.

They wrote back that I was correct that the low end of the "confidence interval" in their report "would indicate that the results were similar in treated and non-treated areas."

But that's not actually true. The number in question is a factor of one. Multiplying by one does not produce results that are "similar." It produces results that are the same.

Again, the stakes are high in this. Your daily newspaper, for whatever reason, has told you virtually nothing about the risks. All I am saying is that we all need to demand better answers to tougher questions before we do this again.

We all come to these emergencies with the best of intentions, but few of us leave our egos at home. This is serious. It ain't just baseball.

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Bellinger is half right when he warns that pesticides can have "stealth" effects on brain development in young children. Meanwhile, prevenable diseases like West Nile do most certainly have permanent effects on children, death for instance.


Actually you are quite fast and loose not to mention inconsistent with your use of "can" and "do." West Nile does not have these effects in everyone as some develop the milder form of the disease and more importantly there are safer, more effective ways to control mosquitoes according to entomologists, like the ones noted in this article. It is this very seriousness of West Nile that calls on us to use the most effective mosquito control strategies, which also happen to be the safest. The immature stages of the mosquitoes represent as much as 98 percent of the mosquito life cycle during the mid months and are not affected by adulticide pesticides that are used to aerial and truck spray. Leading entomologist generally agree that targeting the biggest part of the life cycle represented by the eggs, pupae and larvae is the most effective way to control mosquitoes. BTI larvicide kills larvae before they ever turn into adult mosquitoes that can bite and infect humans with West Nile. When mosquito breeding hot spots are aggressively targeted with larvicide it cuts the problem off at the quick. BTI Larvicide has also been used for decades and has shown no insect resistance. The Entomologist at Rutgers University who regularly review the New Jersey Mosquito Plan and make recommendations have said insect resistance is comparable to bacterial resistance to antibiotics, a serious public health threat.  (  They state that spraying should be "avoided" particularly over large "contiguous areas" because of the threat of insect resistance and the public health effects. And yet the county here sprayed almost an entire densely populated county. Sacramento, which has been held up here as an example of successful aerial spraying, specifically avoids aerial spraying populated areas because of the health effects and they ONLY aerial spray because of the 50,000 acres of rice patty fields, which makes it difficult to larvicide. They also emphasize larviciding and public education over spraying. Even though they have sprayed less than Dallas did last summer, they are already experiencing significant insect resistance in Sacramento and have had to start using much more toxic organophosphate pesticides that are in the same chemical family as nerve gas and have been associated with autism, ADHD, lower IQ and cancer in children. And so your dismissiveness of the health effects is inappropriate. The Rutgers entomologist also note that pyrethroids, which were sprayed here last summer, are endocrine disruptors, which have been associated with cancer, and should be used "rarely."   While  BTI larvicide, which is the most effective way to target mosquitoes before they can even bite you, has negligible human health effects, there is a substantial growing body of evidence showing long term health effects in children opposed to low level pesticides. Two major reports were released just in the last couple of months, including one by the American Academy of Pediatrics, offering stern warnings on the effects of pesticides in children. See these links for copies of the reports:   There is also the public health threat of creating a level of resistance where no pesticide is effective in controlling the adults. Spraying also can pose the risk of increasing the larval population, which can lead to more mosquitoes, which is exactly what happened according to the CDC report. The only long term study of aerial spraying in New York's  Cicero Swamp found 11 years of sprayng there led to a 15 fold increase in the disease carrying species of  mosquitoes.  There can be a time and a place for using adulticides, but they are best used in an extremely targeted and limited way so as to not lead to resistance, killing off of predator insects, disruption of the ecocystem that is driving the explosion of diseases like West Nille according to leading research, and insect resistance. (  Leading integrated pest management experts say targeted spraying should only be a last line of defense after implementing an intensive program of larviciding, source reduction, code enforcement and education, which is the best, most effective, safest approach. It's also important to consider the secondary public health effects of spraying that can result from insect resistance. IF we eventually create a mosquito that no longer responds to the limited pesticides we have, we can end up in a situation where we have no effective adulticides to use in the middle of an outbreak, much like we are seeing happening with certain bacterial infections that no longer respond sufficiently to the current arsenal of antibiotics.