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8-14-02
Well, eventually it had to happen...... after all, pendulums do swing. As the number of human cases of WNV increases, along with further mortality (in total number, not in rate), some states have adopted a strong program of mosquito control with pesticides. In Louisiana where almost all WNV human mortality has occurred, weekly spraying was modified to daily spraying. As the article below summarizes, ever wonder about all those pesticides being sprayed in the air? All mosquito control programs I know use organophophates. These pesticides, while very short lived relative to the organochlorines, are neurotoxins (as I noticed the article accurately points out) and have the potential for effects on vertebrate species. I really like the comment of the Jefferson County (AL) Public Health Department regarding spray trucks, public sense of security and "something being done". Hmmm...... makes you wonder about short term payoffs.
New distributions for WNV recently: horses in South Dakota (most on the eastern side, but one case in Butte Co, against the Wyoming/Montana border)and Kansas. The disease has been found in 35 states and Washington DC during 2002 so far. Expect it to be close to nationwide by next year. So far 130 cases (including some unconfirmed cases) of equine WNV have been reported most in Florida, Texas, Mississippi, and Louisiana. Put into perspective: the equine population of Texas alone is estimated at 1 million animals.
Speaking of WNV human mortality, have you noticed that the distribution has shifted south and west? WNV has received national attention because of its new introduction to this country and our surveillance monitors its spread westward. But as with the many viral encephalidities in this country (e.g. St. Louis encephalitis, eastern and western encephalomyelitis, La Cross encephalitis) once populations develop endemic disease the number of cases drops as exposure translates into at least partial immunity. CDC reports this is likely to happen with WNV and that makes sense. It also explains why the high human caseload is occurring in Louisiana, Mississippi and Texas this year compared to Florida, Georgia and mid-Atlantic states last year. Some cases of St. Louis encephalitis, and recently a mortality in Wisconsin from La Cross encephalitis reminds us that these other viral diseases remain in this country. A human WNV vaccine is under investigation. Recombinant ues are being used to develop the vaccine (using Yellow Fever and Dengue viruses). Human trials scheduled for this summer. Lastly, there have been a few new cases of BSE recently, including Netherlands (41st case), Luxembourg (only its 2nd case) and Germany (83rd case). More importantly is the new case in UK commonly referred to as BAB (Born after Ban, referring to banning of feeding meat and bone meal (MBM) to ruminants) or BARB (Born after Real Ban, noting that the original ban in 1988 was ineffective, but the newer restrictions in 1996 supposedly corrected this sieve). This newest case was born in 1998 and represents the BARB case known. The BARB cases have created debate on source. On one hand, BARB cases were predicted based on some, but minor, maternal transmission. On the other hand, very few if any BARB cases can be traced to a maternal origin. The EU steering committee will be revisiting this.
Thomas J. Roffe, PhD, DVM
Northern Rocky Mountain Science Center
USGS-BRD
FWP Bldg, 1400 S. 19th Ave.
Bozeman, MT
T: 406-994-5789
F: 406-994-4090
Cell: 406-539-4955
Supporting Documents:
Date: Sun, 11 Aug 2002 15:30:02 -0400
From: Joseph R Parrish Jr <JoeParrish@compuserve.com>
Source: ABC News 11 Aug 2002 [edited]Useless Spraying? West Nile Deterrent May Not Be Best Solution
If you live in one of the 34 states where West Nile virus has been discovered, should you draw comfort from the clouds of pesticides being sprayed into the air to kill off mosquitoes? Maybe not.
"The chemicals have not been adequately tested for their human healtheffects," cautioned Dr. Sheldon Krimsky, a pesticide-risk expert at Tufts University. "There is a lot of circumstantial evidence that they cause cancer in animal studies, that they are hormone disruptors. Remember, these are neurotoxins," Krimsy said, adding that most studies done on the effects of spraying focused on agricultural spraying, not spraying in populated areas. "We simply don't know what effects it's going to have, the indiscriminate spraying on human populations," he added.
So far this year, officials have reported 112 human cases of West Nile, more than half in the past week, according to the Centers for Disease Control and Prevention (CDC). Most of these infections are in Louisiana. Mississippi and Illinois also have reported human infections of the virus. Residents Protest Pesticides [others demand them]
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In Hays County, Texas, residents effectively stopped spraying in many of their neighborhoods. They protested, carrying posters decrying the "chemical warfare" on their families. County commissioners agreed to severely limit mosquito spraying near those homes. In Jefferson County, Alabama, health officials are trying to decide what to do. Many cities, including Birmingham, have been spraying for weeks. County officials, though, haven't started their own spraying efforts because they aren't convinced spraying is all that effective against mosquitoes. But after a case of West Nile infection was recently discovered in Alabama, some residents began demanding that the county spray.
Brian Debrow, the environmental health program manager at the Jefferson County Health Department, says the county may start spraying in order to ease anxiety. "The public likes seeing the trucks going down the road and spraying for mosquitoes," he said. "It gives them a sense of security. They feel like something is being done."
CDC: Least Effective Deterrent
Scientists at the CDC, which is leading the surveillance effort on West Nile virus, do not take a position on whether local health departments should spray for mosquitoes. But they do point out that spraying is the least effective method of slowing the spread of the insects. Since adult mosquitoes only live for about 2 weeks at the most, the most effective way to limit mosquitoes is to keep them from breeding. And that means emptying out pools of water where they lay their eggs.
That's exactly what Washington, D.C. health officials are doing. They've decided that spraying pesticides into the air is too risky, especially since the incidence of asthma in the city is already high. Instead, they are targeting small amounts of pesticides directly into pools of standing water and ditches where mosquitoes are breeding. And they're going door-to-door with pamphlets that explain to residents how best to avoid mosquitoes altogether. Even so, in the states where West Nile virus has been discovered, there is pressure on health officials to appear to be fighting the virus on every front and many feel the most convincing approach is the most visible one: spraying chemicals out where everyone can see.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://biology.usgs.gov/cro/WNV8-14-02.htm
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