spraying. http://www.newsday.com/news/daily/spra1107.htm
November 7, 2000
Doubts About Spraying - Some experts call it ineffective against West Nile
virus
by DAN FAGIN
Staff Writer
On the ground and in the air, the war on West Nile virus is over in New
York for this year. But some experts and activists are increasingly
wondering whether one of the chief weapons, insecticide spraying, has made
much of a difference in controlling the spread of the mosquito-borne virus.
There have been just 13 confirmed West Nile-related illnesses this year in
New York State, down from 69 last year. But the virus that was first
confirmed in the United States just more than a year ago in Queens
continues to spread geographically and has now killed birds in 11
northeastern states. Spraying has stopped for the year because the cooler
weather has reduced mosquito activity.
While scientists from the federal Centers for Disease Control and
Prevention and other agencies are tracking the virus and have launched an
all-out effort to understand how it spreads, virtually no research is under
way on the effectiveness of spraying. Insecticide application, especially
from the air, has been the most controversial aspect of the West Nile
effort, spurring numerous lawsuits and protests around the region.
In fact, 14 months after local governments throughout metropolitan New York
began deploying spray trucks and helicopters to fight West Nile, health
officials at all levels of government still have released only rough
estimates, not specific data, about how effective spraying has been in
killing disease-carrying mosquitoes.
"We need to address this, because if we're just spraying all over and not
doing a damn bit of good, then this is a waste of time and money, and it's
also a hazard,” said David Pimentel, a professor of entomology at Cornell
University and a longtime pesticide researcher.
Up to now, the debate over spraying has mostly centered on the health risks
of products such as Anvil, Scourge and malathion. According to the U.S.
Environmental Protection Agency, all three pose acceptably low health risks
to people when sprayed at the very low dosages specified on the label.
Increasingly, however, critics and some researchers are suggesting it's
just as important to look at whe- ther the sprays are an effective way of
controlling West Nile. That's especially important, they argue, as evidence
accumulates that the virus only rarely causes severe illness in the people
it infects, and it can be transmitted by seven or more mosquito species,
each with different breeding, flying and biting habits.
Last week, researchers at the federal National Wildlife Health Center in
Wisconsin added to the confusion over how best to control West Nile by
confirming that mosquitoes are not the sole vector for the virus, which can
also pass from bird to bird.
"There's not enough evidence that all this spraying has changed the dynamic
of the outbreak, and that's in part because the studies really haven't been
done to find out,” said Michael Hansen, the chief pesticide researcher at
Consumers Union, which publishes Consumer Reports magazine.
The architects of the campaign to control West Nile acknowledge the lack of
scientific evidence. Getting it, they say, is a daunting challenge that is
necessarily less urgent than understanding the details of how the
potentially lethal virus is transmitted.
In the absence of stronger evidence, advocates of spraying argue that the
relatively low rate of severe human illness this year -- there have been no
deaths in New York State in 2000 from West Nile, and just seven last year
-- demonstrates that insecticides, along with public education and efforts
to eliminate mosquito breeding sites, is keeping most people safe even as
the virus spreads geographically.
"We've always said there's no way we could break the transmission cycle in
nature and stop this virus from spreading without doing a lot more spraying
than would be acceptable to the public,” said Dr. Stephen Ostroff, a senior
CDC official who is coordinating a nationwide effort to control the virus.
"So our perspective on the use of pesticides is that we're trying to reduce
the risk of illness to humans, and there's no question that we've succeeded.
"One could argue that the number of human cases would have been low anyway,
even without spraying. We'll never know the answer to that, and I don't
necessarily want to know, because I'm not going to recommend that local
communities put people at risk by not using all of the appropriate control
measures.”
Critics and supporters of insecticide spraying agree on one thing: It's not
the most efficient way to control mosquitoes.
Studies have consistently shown that, on average, less than one-tenth of 1
percent of the millions of droplets released from a helicopter or plane
during a typical spraying run actually hits a mosquito, according to
Cornell's Pimentel, who believes spraying is nonetheless justifiable in
some circumstances.
In addition, he said, if there are numerous trees, buildings or other
obstructions in the area, the spray cloud will almost certainly miss large
areas of the target zone, including mosquitoes inside buildings.
For those reasons and others, the consensus among experts is that educating
the public about how to avoid being bitten, eliminating breeding sites and
killing larval mosquitoes with less-toxic sprays before they take wing are
all more efficient than trying to kill adult mosquitoes with pesticides.
But health officials in New York City, Nassau, Suffolk and other local
governments around the region said even though they emphasized preventative
measures this spring, by midsummer, their surveillance efforts were showing
that many mosquitoes and birds around the region were infected, often in
densely populated areas. At that point, they said, spraying was the best
control option left.
The debate over whether they made the right choice is especially
complicated because it's so difficult to measure or even define a
successful pesticide application.
"It's just not a straightforward thing to measure the efficacy of a large
spray, because weather and other conditions can vary so much from place to
place and from hour to hour,” said Dominick Ninivaggi, who heads the
mosquito-control program in Suffolk County, the most extensive in New York
State.
Local health officials say they have undertaken some small-scale
experiments by trapping and counting mosquitoes before and after an area is
sprayed. They haven't released their data because, they say, they're still
analyzing it.
"We agree that effectiveness is an important question, and we intend to
answer it,” said Dr. James Miller, West Nile coordinator for the New York
City Health Department. Suffolk also says its data isn't ready for public
disclosure, and Nassau officials did not return phone calls.
Though they haven't released any data, Miller and other New York City
officials estimate that in the city, mosquito counts after a spraying are
"up to 85 percent” lower than they were beforehand. And Deputy Commissioner
Carl Johnson of the state Department of Environmental Conservation, which
regulates pesticide use around the state, said local governments have
anecdotally reported "60 to 80 percent reductions” after spraying.
Some mosquito-control experts from outside the region, however, are
skeptical. "I find it hard to think that they could consistently get 85
percent control spraying in an environment with so many trees and houses
and other obstructions. But I'd really have to look at the data to know for
sure,” said Judy Hansen, a past president of the American Mosquito Control
Association who has run the mosquito-control program in Cape May County,
N.J., for 40 years.
"The people in New York ought to be very cautious about saying they're
getting 85 percent control,” agreed Ray Parsons, who runs Houston's program
and was a consultant to Rockland County this year.
Trap experiments in residential areas in Florida, the state with the most
extensive mosquito-control experience, generally show a reduction of about
30 percent after a spraying, "and that's also about what we get in
Houston,” Parsons said.
Figuring out whether spraying is keeping people from getting sick is even
more difficult than determining how well it's killing mosquitoes.
The CDC is in the midst of an extensive West Nile study aimed at measuring
human infection rates in portions of Staten Island, Babylon and Stamford,
Conn. But the agency isn't even attempting the daunting statistical task of
looking for a link between the infection rate in each community and the
amount of insecticides sprayed there.
"The simpler questions about infection rates need to be answered first,”
said the study's director, Dr. Anthony Marfin of the CDC.
Several years ago, Pimentel reviewed spraying records in Memphis, Dallas
and several other southern cities to see if the number of St. Louis
encephalitis cases declined significantly after spraying. Pimentel said he
concluded that the question couldn't be answered scientifically because
there weren't enough diagnosed cases to be statistically meaningful.
West Nile, he said, triggers severe illness even more rarely than the St.
Louis virus, so it will be even more difficult to design a meaningful study
to gauge the effectiveness of spraying.
Another dilemma is that one of the most scientifically sound way of
studying the problem -- by comparing two nearly identical communities with
high infection rates -- would require leaving one of those communities
unsprayed despite evidence that people who live there are infected with the
virus.
"That's just not going to happen,” said Johnson of the state DEC. "It's a
risk no one in public health would ever take.”
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