On the op-ed page of The Dallas Morning News this morning, two local epidemiologists with national/international reputations weigh in for more aerial spraying to combat West Nile disease. Robert Haley, the Gulf War Syndrome expert, and James Luby, an expert on St. Louis encephalitis at UT Southwestern, call for some kind of agreed upon trigger in human infection rates to launch an airplane spraying campaign like what we saw in Dallas last summer. Their credentials can't be questioned, but their piece in the paper this morning can be. Some elements of it, especially where they tout a recent Centers for Disease Control and Prevention study of our spraying campaign last year, amount to two pretty heavy thumbs on the scale.
Haley and Luby say in their piece this morning: "An independent study by the CDC scientists concluded that the epidemic ended more quickly in sprayed areas." They're right about that, if you look only at the narrative summary of the CDC report, which said, "The aerial spraying measures implemented for [West Nile Virus] control had a measurable impact in preventing WNV neuroinvasive disease."
But as we reported in the paper last February, when you drill down just a little into the actual numbers in the report, that summary starts to look pretty glossy and maybe even a tad propagandistic. In fact what the report really found was that human infection rates may have fallen six times faster in sprayed areas than nonsprayed, or the rates may not have fallen any faster at all. And that's a straight-up coin-flip. The CDC can't tell you which answer is right.
The CDC arbitrarily dropped from its study one of the two forms of the disease after noting that the numbers for that form seemed not to conform to their conclusion. The CDC study also found that mosquito populations here actually increased during spraying.
And that brings us to a curious wording in the Haley/James piece, where they refer to it as "an independent study." What is that term, independent, intended to convey? That the study was objective? That it was not colored or conflicted by outside or internal bureaucratic interests?
If that's what they mean, then it's a conclusion to which the two distinguished scientists have jumped a little glibly. If the CDC really wanted to persuade us its study was objectively scientific and not self-serving, then it might have included in the report some explanation of the enormously wrong, very public, very argumentative statements its staff made last summer.
Immediately after the spraying, CDC personnel endorsed a finding that the airplane spray was 93 percent effective at killing dangerous mosquitoes. But the second report a half-year later found that mosquito populations actually increased during spraying.
Is it unfair to wonder if the summary conclusions of the later report, which come down hard on the positive side of some awfully indeterminate numbers, may represent the agency's attempt to cover itself for the huge goof on kill rates? Does that possibility at least put a dent in their credibility?
Haley and Luby indulge in a number of other soft generalizations, including one about other major cities that have "regularly pre-empted epidemics with aerial spraying." There again, a little bit of drilling down is in order. The city most often cited, Sacramento, California, sprays a vast surrounding heavily irrigated agricultural area, mainly in South Sacramento County, but does everything it can to keep the spray out of residential areas.
The pair asserts confidently that the chemicals sprayed have "low potential for human toxicity" specifically for newborns. This assertion ignores growing evidence, some of it from the University of Texas at Austin (and the University of Michigan, a school never to be ignored), some from European researchers, who are finding that endocrine disruptors used in these sprays may affect prenatal and early infancy brain development.
Haley and Luby conclude that, "Opponents of aerial spraying offer hypothetical, scientifically unsupported claims." I'm sure that happens. But the opponents also have brought to bear a good deal of serious science from people with serious credentials who tend to argue two things: 1) Spraying pesticide from airplanes is the single most inefficient of all the available means for killing mosquitoes, and 2) The chemicals sprayed may pose human health risks that outweigh the risk of West Nile.
My own worry is this. Used in isolation from other methods, aerial spraying is the lazy man's approach to health generally -- push-a-button, take a pill, don't forget to pay your bill. The far more effective methods for controlling West Nile are the measures aimed at killing mosquito larvae where mosquitoes breed. But those methods are messier, muckier, harder to do. They involve lots of public awareness about standing water, but they also necessarily involve sending out paid personnel to invade neglected back yards with stagnant swimming pools and the like.
The real experts where those methods are concerned tend less often to be UT Southwestern scientists and more often people like Howard Garrett, Dallas' own "Dirt Doctor" and proponent of organic land management who is encouraging the city to use BTi, a bacteria-based bug-killer, instead of chemical toxins and endocrine disruptors that attack human physiology the same way they do insects.
This is not to say Haley and Luby are flat wrong to call for a trigger rate in human infections, agreed upon ahead of time by public officials so that aerial spraying can be invoked as a last resort. The danger, however, lurks in the argumentative tone of their piece this morning -- spraying here last summer was a big success, opponents of spraying are unscientific, public debate on the issue is "politically paralyzing."
That last one I find especially troubling. I don't remember any paralysis caused by political debate. What I remember is a little bit of talk and then a whole bunch of airplanes. These guys are both epidemiologists: Why don't they go back and carry out some kind of scientific study to see how many people suffered paralysis caused by political debate?
Just as it would have been nice to see the CDC tackle its own broad-side-of-a-barn mistake on kill rates last summer, it would have been reassuring to hear Haley and Luby say they do recognize the superior effectiveness of larvicides over aerial spraying for control of mosquito populations. Given their distinguished credentials and careers, both men certainly know that much.
Why would we blunder into this again without calling for some kind of serious colloquium on the risks of spraying? Between Big Chem and Texas A&M, we've already got too many people and too much money with self-serving agendas on this issue. Shouldn't we at least try to sort out some truth from the aggressive salesmanship?
The vast preponderance of the scientific evidence argues that aerial spraying should be a distant last resort. Haley and Luby may be right we need a trigger, but what we do not need is a hair-trigger.
