- West Nile Story
- When Mosquito Control District Fails To Control Mosquitos
- By Brenda Fowler
- Chicago Tribune
- 11 May 2003
- What do you get when a mosquito control district fails
to control mosquitos?
- You get SICK!
- Last July 23, a crow plummeted out of the sky and landed
in a yard near the intersection of South 55th Avenue and West 91st Street
in Oak Lawn. The homeowner phoned the village hall and, since it was Oak
Lawn's first such call, sanitation inspector Jeanne Foody Galzin came to
collect it that same day. Galzin double-wrapped the crow in plastic, as
she had been instructed, and sent it off to be tested.
- When the results came back a week later, they confirmed
fears that the crow was positive for West Nile virus, the mushrooming scourge
that is potentially fatal to both humans and birds and can be transmitted
through the bite of a single mosquito.
- By that time, the July skies had begun to rain crows
across Cook County. In Oak Lawn they fell from the magnificent elms that
tower over lawns behind brick bungalows and tidy ranch houses, and littered
the roads and roofs and cemeteries that rim the southern border of this
mature suburb of 55,000. No one asked Oak Lawn to keep track of how many
birds were reported dead, nor did they.
- "It was a lot," says Galzin tersely.
- Illinois public health officials already knew something
frightening was brewing. They had been on the lookout for West Nile virus,
an import from the Middle East, ever since it showed up in New York City
in the late summer of 1999. The virus had spread at an alarming pace. By
the end of 2000, presumably moved along by birds, West Nile had reached
into North Carolina in the south and Vermont and New Hampshire in the north.
- A year later, it entered Canada and spilled into the
Midwest. During the fall of 2001, more than 100 birds died across the northeastern
corner of Illinois. Infected mosquitoes were detected as well, but no human
- The earlier in the year birds begin to die, the more
likely it is that the infection will have time to infiltrate the human
population, says Linn Haramis, an entomologist who is manager of the vector
control program at the Illinois Department of Public Health in Springfield.
"Last year," he says, "we had our first dead bird on May
2, and I thought, 'Uh-oh.' "
- By Sept. 10, Haramis' vector control department (vectors
are the carriers that transmit disease) was reporting 292 human cases,
more than any other state had seen in one year. Several states had similar
attack rates--the number of people who got the disease per 100,000 population--but
for sheer numbers, no state matched the toll in Illinois: In all of last
year, 877 people were diagnosed with West Nile virus and 63 died.
- Most people who become infected never know it because
they do not get sick. Others display flu-like symptoms, a mild form of
the illness that doctors call West Nile fever. But another group develops
one of the two major complications: encephalitis or meningitis, inflammation
of the brain or brain membranes, respectively. The group with these conditions
is relatively small. According to the U.S. Centers for Disease Control
and Prevention, only about 1 in 150 people infected with the virus will
develop a severe form of the disease.
- But the effects can be long-lasting. Seven months after
the last person was infected last fall, some of those with complications
still have not fully regained their health, says Mark Dworkin, the state
epidemiologist at the Illinois Department of Public Health. There is no
treatment for the virus and, so far, no vaccine.
- Last year, 634, or 72 percent of the state's West Nile
cases occurred in Cook County--not surprising, given the density of the
population. But curiously, the cases clustered in two areas within the
- One, toward the northern end of Cook, was centered in
Skokie and Evanston, which together reported more than 80 cases and two
deaths. The other was on the opposite side of the county, in the southwest
suburbs of Oak Lawn and Evergreen Park. There, in an area no bigger than
12 square miles--just 1.2 percent of the area of the entire county--52
people were infected by the virus and three of them died. The number represents
more than six times the rate of infection for the rest of Cook County.
- Together, the two clusters accounted for 21 percent of
the county's cases and nearly 8 percent of all West Nile deaths in Illinois.
- Why so many people in these apparently ordinary suburbs
got sick has much to do with the inscrutably complex interaction of the
birds that harbor the virus, the mosquitoes that transmit it, the humans
and other creatures who are bitten by them, and the ever-changing environment
in which they live--the waters, green spaces and climate.
- But the answer may also lie in how well local mosquito-control
agencies did their jobs.
- The first person to offer an explanation for the Oak
Lawn-Evergreen Park cluster was Dr. Khian Liem, general manager of the
South Cook County Mosquito Abatement District (MAD), whose territory covers
340 square miles of southern Cook, south of 87th Street between Indiana
on the east and DuPage County on the west. It includes Oak Lawn and Evergreen
- A quietly confident man, Liem, 61, has been with the
South Cook MAD since 1974 and became its manager in 1976, a year after
another mosquito-borne viral disease, St. Louis encephalitis, infected
more than 578 people in Illinois, killing 47. Oak Lawn and Evergreen Park
were a focus of that outbreak too.
- Liem hypothesized at that time that the many cemeteries
rimming the two suburbs provided the perfect meeting ground for birds that
carry the virus and the mosquitoes that transmit it. In interviews with
local media last summer, Liem again pegged the cemeteries as the problem.
- "They're very wooded areas where mosquitoes have
their nests," Liem told the Daily Southtown last September. "A
lot of people come to visit their loved ones. And when you live near these
areas, you're practically surrounded."
- But even as Liem was blaming the cemeteries, his own
surveillance and abatement efforts were coming under scrutiny by the West
Nile Virus task force, a multi-agency group chaired by the Cook County
Department of Public Health that began meeting regularly last summer as
the outbreak developed.
- Some officials now say that Liem failed not only to adequately
monitor the populations of mosquitoes in his district, but also to control
their breeding and rid his district of adult mosquitoes, many of which
were infected with West Nile virus.
- "I think strong and accountable mosquito control
is important, and I don't think we had that," says Dr. William Paul,
the deputy commissioner of health for the Chicago Department of Public
Health. Paul and other public health officials say they still have not
received detailed information from Liem about his abatement efforts last
- But interviews with employees of the South Cook MAD and
records obtained from Liem reveal that in most parts of his district, including
Oak Park and Evergreen Park, employees did not begin applying pesticide
to catch basins where mosquitoes breed--a process called "larviciding,"
which is considered the most fundamental element of a mosquito-control
program--until two months after other abatement districts had done the
job, and well after his lab had detected high numbers of infected mosquitoes.
On some streets, records show, larviciding--which usually involves dropping
larva-killing oil or briquets into catch basins--was done only after residents
lay deathly ill in the hospitals.
- he four mosquito abatement districts serving Cook County--South
Cook County, Des Plaines Valley, Northwest and North Shore--are independent
agencies supported primarily by local property taxes. Charged with the
surveillance and control of mosquitoes, each district is licensed to apply
pesticides by the state Department of Agriculture and required to report
annually on its operations to the Illinois Department of Public Health.
- One of their primary jobs is surveillance--identifying
breeding sites and then trapping, counting and identifying adult mosquitoes
to determine how dense they are at any given time and place. When a dangerous
virus like West Nile lurks, good surveillance is crucial.
- Before the emergence of West Nile virus, the abatement
districts focused their treatments on the hard-biting floodwater mosquito,
Aedes vexans, which emerges after rainfalls to pester people during their
summer barbecues. But researchers think that it is the northern house mosquito,
Culex pipiens, that is primarily responsible for transmitting West Nile
virus from birds to humans, because human cases start to appear soon after
large numbers of infected Culex are identifed.
- In August 2001, even before the first dead crow was discovered
in Illinois, West Nile was detected in Culex pipiens in Illinois by Don
Oemick, an entomologist with the Northwest MAD. Researchers at the Illinois
Natural History Survey's Medical Entomology Program in Champaign have since
detected West Nile virus in 11 other species of mosquitoes in the state.
- In northern climes, like Illinois', the viral transmission
cycle is interrupted in the winter when mosquitoes either die off or go
into hibernation. Then, in early April, the female Culex restuans, which
is related to Culex pipiens, emerges from its winter hiding places, such
as storm tunnels, and flies off to find a blood meal. From this blood the
females get the proteins necessary to develop their eggs. Culex mosquitoes
prefer to feed on birds, many of which migrate during the winter, but pipiens,
especially, will also bite mammals, including humans. Precisely how the
cycle works is not yet clear.
- According to Richard Lampman, a research entomologist
at the Medical Entomology Program laboratory, the fact that some mosquitoes
can harbor the virus through the winter and start infecting birds as soon
as they emerge probably accounts for the ever-earlier appearance of the
virus. At the same time, uninfected mosquitoes, which rarely make it more
than a mile or two from their birthplace, pick up the virus when they bite
viremic birds--those with the virus in their blood. Viremia starts a day
or two after a bird is bitten and usually lasts three to seven days. Among
the virus' avian hosts are crows and jays, which often die from the infection,
and cardinals, house sparrows and robins, which usually do not. Once a
female mosquito bites a viremic bird and picks up the virus, it can work
its way to her salivary glands and then be injected into everything she
bites after that. Typically, a female takes several blood meals in her
- As the weather grows warmer, the number of Culex restuans
begins to decline and Culex pipiens emerges. Birds infected by Culex restuans
are bitten again by Culex pipiens, which may then go on to bite humans
or other mammals, such as horses, dogs or squirrels. The virus does not
build up enough in mammals to be passed back to mosquitoes, though it can
be passed to other humans via blood transfusion and even breastfeeding.
- The first infected Culex Oemick captured came from a
gravid trap he set up near the Des Plaines River in Northbrook. The gravid
trap, basically a bucket of rotten-smelling grass and water overhung by
a net, takes advantage of the fact that Culex females like to lay their
eggs in water rich in organic matter, such as stagnant ponds or basins,.
Attracted to the scent, the females approach the trap and are sucked into
the net by a weak vacuum.
- Last May, Oemick set out 13 gravid traps around his 241-square-mile
district, as well as 13 light traps, which capture mosquitoes by attracting
them to a light source. Nearly every day, Oemick and his staff collected
the mosquitoes, sorted them according to species, and tested them. Then
he sent them by overnight mail to Lampman at the Medical Entomology Program
lab for more sensitive testing.
- While Oemick ran surveillance and testing, more than
50 summer employees, mainly college students, fanned out through the district,
which covers the northwest corner of Cook County, applying larvicide to
stagnant water sites for Culex eggs, and to areas prone to flooding after
rains, where Aedes vexans lay their eggs.
- Among the most important stagnant-water sites on the
list were the district's 132,000 catch basins, the large, bucket-like containers
that lie beneath most sewer grates. When water runs through the grate into
the sewer, it drops several feet into the catch basin, bringing along dirt,
branches and clumps of leaves and grass that settle to the bottom. After
water reaches the top of the catch basin, it flows into the sewer pipe,
which opens two or three feet above the bottom of the basin.
- Because catch basins retain stagnant, dirty water, they
are notorious breeding sites for Culex, especially in dry periods when
fresh rains haven't flushed out the larvae. Though the work is labor intensive,
the Northwest Abatement District, which last year had a budget of about
$1.8 million, tries to treat the catch basins at least once a month with
methoprene, a larvicide. It comes in briquet form and can be dropped through
the sewer grates into the catch basin, where it dissolves slowly over a
- "Larval control is the primary and most effective
method of controlling mosquitoes, and catch basins are an important aspect
of that," says Robert Holub, manager of the 78-square-mile Des Plaines
Valley MAD in Lyons, which last year had a budget of $1.1 million and ran
operations similar to those in the Northwest MAD. "If you only have
X amount of money to spend, larval control is the way to do it."
- As temperatures warmed late last spring, the South Cook
County MAD, which is the state's largest but which had a relatively small
budget last year of about $1.7 million, began its surveillance and larviciding
operations. In Oak Lawn, crews focused mainly on ditches along the Metra
tracks, parks and waterways, and the cemeteries and the streets around
- Mike Slamecka, a biologist who runs South Cook's lab,
had half the number of traps of the Northwest district--eight light traps
and five gravid traps--and they were spread out over a much larger area.
The closest to Oak Lawn was a gravid trap hidden along a fence in Mount
Greenwood Cemetery in Evergreen Park. Slamecka sent all the mosquitoes
collected to the Medical Entomology Program lab in Champaign for testing.
- round July 20, roughly the same time that the first infected
crow was falling into the yard in Oak Lawn, Slamecka learned that a "pool"
of mosquitoes that he had sent from the Mount Greenwood trap was positive.
That meant that at least one specimen in the pool, which usually contains
50 mosquitoes, carried the virus. It was the first time West Nile virus-infected
mosquitoes had been detected in the area. Five days later, he had four
positive pools, including two from Mount Greenwood. Slamecka did not keep
track of how many pools he was sending in, but he did realize that almost
every pool from Mount Greenwood was showing up positive.
- "We weren't surprised that there were positives,"
says Slamecka. "It was the magnitude of it."
- The last positive from Mount Greenwood was on Aug. 2.
At that point, the trap was stolen, and, though it had been providing key
information, it was not replaced. Meanwhile, at the Medical Entomology
Program lab, where mosquitoes from around the state were being tested,
Lampman was monitoring the sudden surge in the percentage of positive mosquito
pools--from none in early July to 5 percent to 10 percent of all pools
by the middle of the month--from the abatement districts in Cook County.
Lampman and the lab director, Bob Novak, were concerned that the number
of infected mosquitoes was already high enough to put humans at risk.
- But neither man could have predicted what came next.
- "Two weeks later, we pooled and plotted, and [the
number of positive pools had risen to] over 75 percent," says Lampman.
- In the Des Plaines Valley MAD, the percentage of positive
pools rose to more than 90 percent. "This is something we had never
seen before with [this kind of] virus," says Lampman. "If someone
had told you that 90 percent of the pools would have been positive, you
would have said it wasn't possible. It was brand new to all of us. And
- According to Dr. Roger Nasci, a research entomologist
with the Centers for Disease Control and Prevention, the positive pool
rate suggested that in some localities, at least 20 of every 1,000 mosquitoes
were infected. But a new analysis by Wei Dong Gu, a biological modeler
at the Medical Entomology lab, suggests that the infection rate might have
been two to three times higher, or as many as 60 infected mosquitoes per
thousand. By contrast, during the 1975 St. Louis encephalitis outbreak,
only about 3 per 1,000 were infected.
- West Nile's human incubation period--the time from the
bite to the onset of symptoms--is between 3 and 14 days. Health officials
didn't have to wait long to see the virus spill into the human population.
On Aug. 6, the Illinois Department of Public Health reported its first
case: a 22-year-old student from Maryland who had been living in Cook County
and working with birds. The young woman had mild symptoms and recovered
quickly. But just 10 days after that report, four new cases were announced,
including that of a 70-year-old man from Oak Lawn who lived just two blocks
from the spot where the village's first dead crow had fallen.
- The man had first felt unwell on Aug. 3, says his wife,
who does not want the family's name used. Three days later, he was hospitalized
with a fever of 102.4 degrees.
- Still unaware that the man had West Nile virus, doctors
operated on him for an unrelated problem that they thought was causing
the fever, his wife says. Immediately following the procedure, he seemed
better, but when she came in the next day, he was on a respirator. His
fever had risen to 105 and doctors, who had begun to suspect West Nile
virus, ordered a spinal tap that revealed encephalitis. Not until almost
a week later did they confirm West Nile.
- By that time, says his wife, the man had suffered brain
damage and was unresponsive. For most of the next five weeks, he stayed
under intensive care and then was transferred to a nursing home, where
he died three weeks later.
- "I had to take him off the respirator myself,"
says his wife, who wonders if he was bitten by a mosquito in their back
yard. "He was a great feeder of birds," she says. A family of
about 25 crows frequented their back yard, and last summer they had found
- On the morning of Aug. 12, another Oak Lawn resident,
Bennie Casalina, took a few steps out of his bedroom and collapsed next
to the dining-room table. Casalina, a bear of a man with a full head of
gray hair, doesn't recall anything of the next three weeks, but for his
wife, Yvonne O'Neill, it was a nightmare.
- Emergency room doctors at Advocate Christ Medical Center
in Oak Lawn initially thought Casalina had suffered a stroke, because his
left side was paralyzed. But two weeks after his arrival at the hospital,
a test revealed West Nile antibodies. After months of rehabilitation, Casalina
says he feels amost back to normal.
- Typically, West Nile victims have such symptoms as headache,
fever and sometimes a rash. If they have progressed to encephalitis or
meningitis, they will display confusion and lethargy. But of the 56 West
Nile patients seen at Advocate last year, several came in with symptoms
not previously associated with West Nile---mainly paralysis and other neurological
consequences of brain inflammation, according to Dr. Stephen Sokalski,
the hospital's director of epidemiology and head of its infectious disease
section. Four of the 56 died.
- "The sicker they came in, the likelier the fatal
outcome," says Dr. Mel Wichter, a neurologist at the hospital who
treated Casalina. "But the fatality rate is really, really small."
- By the second half of August, epidemiologists had begun
to notice the clusters of cases developing in Oak Lawn-Evergreen Park and
in Skokie-Evanston. Barb O'Meara, an environmental health specialist with
the Illinois Department of Public Health, was quickly dispatched to set
up gravid and light traps at five sites in Oak Lawn. O'Meara and a colleague
from the Cook County Department of Public Health then began visiting sites
where humans had become infected, looking for mosquito breeding sites and
other factors that might explain the cases.
- At their first stop, a man led her to a catch basin set
in the grass of his back yard to drain water that collected there during
heavy rains. The man said his wife had noticed mosquitoes flying up through
the grate. Three doors away, O'Meara found another back-yard catch basin.
- "That's when I called the sewer department,"
says O'Meara, who would learn that, decades ago, Oak Lawn had installed
between 1,000 to 2,000 catch basins in poorly drained backyards but had
failed to keep a record of them because they weren't on city property.
- The sewer workers lifted the grate off one of the basins,
and O'Meara dipped a ladle-like tool into the stagnant pool. Inside the
filthy water, mosquito larvae were clearly visible.
- "They hatched out, which told me that that catch
basin had not been larvicided," says O'Meara. Over the next few weeks,
at site after site where people had come down with West Nile virus, O'Meara
found undocumented back-yard catch basins with mosquitoes breeding inside,
sometimes just feet away from where the homeowners had their picnic tables.
The mosquitoes did not have to fly in from Oak Lawn's cemeteries; they
were breeding in the very neighborhoods where infected crows were being
- "Every site we visited we were able to establish
that there were mosquitoes breeding on the site or within one to two houses,"
O'Meara says. "It wasn't always the catch basin. At one house there
was a Dixie cup and the Dixie cup was breeding Culex. That's why the personal
responsibility of cleaning and looking in your own yard is so important."
- Meanwhile, the mosquitoes in O'Meara's traps were coming
up positive for West Nile. "Every trap that I had set out in Oak Lawn,
I got positive mosquitoes out of," says O'Meara. "Was the virus
spread through the entire town? Yes, it was, and into Evergreen Park."
- While suggestive, O'Meara's discovery did not entirely
explain the cluster of cases in Oak Lawn. After all, there must have been
breeding sites and infected crows around the homes of people elsewhere
in Cook County who never got sick.
- But public health officials were beginning to wonder
precisely what mosquito-abatement treatments had been undertaken in Oak
Lawn and Evergreen Park.
- Tom Varchmin, the chair of the Cook County task force,
says it had become clear during task-force meetings that the four mosquito-abatement
districts had different philosophies about mosquito control.
- At the Northwest MAD, where the first positive Culex
mosquitoes turned up in mid-July and many dead birds were being found,
Mike Szyska had stepped up his treatments even before the first human case.
Beginning in July, Northwest MAD trucks took to the streets at sunset,
when the Culex become active, spraying pesticide at ultra-low volume in
the areas where positive mosquito pools had shown up.
- "Once you have infected mosquitoes flying around
in an area that could potentially infect more birds or possibly even humans,
the only way to knock them down is by adult mosquito spraying in the evening,"
- Despite assurances that the pesticide was safe, many
residents still were not happy to see the frequent spraying, and many called
to complain. But as the human cases continued to mount, Varchmin and other
officials at the West Nile task force were less concerned about Northwest
MAD's repetitive spraying than they were about what the South Cook district
was doing---or not doing.
- Though Liem and Slamecka, his lab director, attended
task force meetings, Liem's answers about his spraying and larviciding
operations were vague.
- "His statement was 'I do treat'--that was as specific
as we could get out of him," says Varchmin.
- Since Liem's district covers the southern tip of Chicago---where
a surprising number of people had also become infected--city officials
were also pressing him to report what pesticide he had used and where and
how frequently he used it.
- "We at the City Health Department tried to communicate
with the South Cook MAD on treatment of catch basins in its portion of
the city," Dr. William Paul told the Illinois House Human Services
Committee last October during hearings related to public health and potential
bioterrorism. "We could not get a straight answer as to their plans
and carry-through. The story kept changing, and there was no documentation
of what they said they were doing."
- In fact, only a small number of the thousands of catch
basins in Oak Lawn and Evergreen Park had been regularly inspected before
July and they were treated only when they were found to be breeding, according
to maps and records provided by the South Cook MAD, and explained by its
general foreman, Douglas Wright. Not until August did crews start to treat
all catch basins in the streets. The unrecorded ones in homeowners' back
yards were never done.
- In the section of town that includes 101st Street, where
Bennie Casalina lives, crews finally began putting larvicide in the street
catch basins on Aug. 3, but "for some reason," Wright says, they
were pulled off the job before it was completed and did not return until
Aug. 30, by which time several people in Oak Lawn had fallen ill with West
- In the neighborhood that includes both the intersection
where Oak Lawn's first dead crow was discovered and the residence of the
first man who died of West Nile, treatments were similarly spare. On Aug.
19, by which time nearly every catch basin in the Northwest and Des Plaines
Valley MADs had been larvicided at least twice, South Cook finally sent
its workers to drop larvicide into catch basins in that area for the first
- Still unaware of exactly what South Cook was doing, but
increasingly frustrated by Liem's vague responses, other authorities stepped
- "We determined in August that we needed to start
preventive efforts in the Chicago neighborhoods served by the South Cook
MAD from scratch," the city Health Department's Paul testified last
- In Evergreen Park, Mayor James Sexton tried to learn
from South Cook precisely what had been treated in his village. "I
mentioned that I had never seen their trucks or their people, but they
assured me that [the catch basins] were being done," says Sexton.
Unconvinced, he persuaded his board to buy 2,000 larvicide briquets at
90 cents each, which were then dropped into Evergreen Park catch basins
by village firemen who volunteered for the job.
- By the first week of September, the positive mosquito
pools from Cook County had begun to drop off, but the number of people
entering the hospital with West Nile was still high. Public health officials
on the task force agreed that they should mobilize the only tool they had
against infected adult mosquitoes. In areas that showed clusters of human
cases, all streets and alleyways were to be sprayed twice within the space
of a few days.
- The Northwest, Des Plaines Valley and North Shore MADs
did their own spraying. But in southern Cook, county officials hired Clarke
Mosquito Control, a commercial firm, to spray Oak Lawn, Evergreen Park
and several other areas of Chicago and suburban Cook. Part of the problem
was that the South Cook abatement district professes to be cash-short and,
with only one sprayer to its name, says it could not undertake the large-scale
spraying the county envisioned.
- In a letter sent shortly after the spraying operation
to Dr. Karen Scott, then director of the Cook County Department of Public
Health, Liem said his district could not even afford the $500,000 Clarke
was charging for the spraying. And he seemed to want credit for his district's
- "My Trustees should be highly commended and applauded
for being unwilling to spend any monies that the district does not have
and to go into debt by borrowing from the bank," he wrote.
- Not that Liem hadn't tried previously to get more funds
for mosquito control. In interviews during March and April of this year,
Liem pulled out copies of letters he had written in July 2000 to Cook County
Board President John H. Stroger Jr. and nearly two dozen senators and representatives
in southern Cook, complaining that he needed more money to prepare for
the possible arrival of West Nile virus.
- He said his budget had never recovered from being slashed
in 1991 after auditors uncovered a $1.5 million surplus that Liem defended
as a contingency fund for operations and a new building. He said that while
his budget had risen slightly since his complaints in 2000, he had not
gotten the infusion of cash that he said was necessary to brace the district
against West Nile.
- "If I had the manpower, I would have done more surveillance
work and larviciding," Liem says. "But my hands are tied when
I have only 11 or 12 people covering 340 square miles."
- But it is likely that, even if his office had the money,
Liem would not have done the kind of spraying for adult flying mosquitoes
that the county wanted. He doesn't think it works.
- "We don't want people to scream at us when they
see a truck going up and down the street," he says, noting that where
he did spray--for example in the cemeteries--he did not use the synthetic
pyrethroids favored by the Northwest MAD, but real pyrethrin, an extract
from the chrysanthemum, because he believes it is safer for people.
- But generally, he argues, while spraying for adult mosquitoes
may be a "good show" and induce a placebo effect against West
Nile in certain people, it was a waste because scientific studies have
not demonstrated that it works.
- "I was asked many times to compromise and I said,
'How do you compromise knowledge? How do I compromise science?' "
- While entomologists agree that the efficiency of spraying
to kill adult mosquitoes is debatable, they insist that it does kill those
mosquitoes it hits, and thus was worth using, even if the efficiency was
lower than desired.
- "I am very concerned about Dr. Liem's comments marginalizing
the use of mosquito adulticide applications as a component of an integrated
West Nile response program," wrote Dr. Duane Gubler, then director
of the CDC's Division of Vector-Borne Infectious Diseases, in a letter
last October to the county health department.
- So far, no data has been produced illustrating that infections
in Cook County dropped off after the coordinated attack on adult mosquitoes.
Yet a glance at the map of the human cases and the borders of the mosquito
abatement districts suggests a link between the intensity of mosquito abatement
efforts and human cases.
- The two districts with the most mosquito surveillance
and best documented larviciding and adulticiding operations, Northwest
- Des Plaines Valley, had the fewest number of cases. Lampman,
the entomologist, notes that the low number of cases in the Des Plaines
Valley district is all the more striking because of the extremely high
percentage there of positive mosquito pools--more than 90 percent at one
- "It is my own personal feeling that if we had not
brought Clarke Mosquito Control in [to South Cook] to provide additional
services, there was a good chance that there would have been more cases
of West Nile virus and possibly more deaths," says Varchmin.
- At a heated meeting last fall of the Southwest Conference
of Mayors, mayors accused Liem of neglecting his responsibilities in their
communities, which were paying for his services through taxes.
- Some complaints about the operations at the North Shore
MAD, including the use of ineffective mosquito traps and failure to spray
the alleys in Evanston, have also arisen since last summer. In Evanston,
where many people have long been opposed to adulticiding because of concerns
about pesticides, residents were permitted to request that their yards
not be sprayed.
- "If one street had five or six houses that did not
want spray and only eight houses, then it would not be sprayed," says
George Xamplas, an ecologist with the North Shore Mosquito Abatement District.
- No one has yet examined whether there is a correlation
between Evanston-Skokie's sometimes-spotty adulticiding and the human cases.
But in his successful campaign last fall for Cook County commissioner from
the 14th District, which covers Skokie and Evanston, Larry Suffredin drew
attention to press reports that surfaced two years ago alleging improper
hiring practices and abuse of expense accounts at the North Shore MAD.
- "Let's just say that two of the MADs are not doing
the job they should," says Suffredin. He has helped shape legislation
now moving through the Illinois House and Senate that would consolidate
the abatement districts into one covering most of Cook County, and require
better reporting of surveillance results and treatments to local health
- While the relatively low number of cases in the Northwest
and Des Plaines Valley MADs may be attributable to good mosquito abatement,
entomologist Lampman says there must be other factors behind the human
clusters because other municipalities in the South Cook County district
that were not adequately larvicided or adulticided would have seen a concentration
of West Nile cases.
- One possibility that researchers are considering is the
correlation between the number of crows in an area and the number of human
cases. According to O'Meara, the Illinois Department of Public Health investigator,
residents of both Oak Lawn and Evanston reported large populations of crows
in their areas before the outbreak.
- Last summer, Sarah Yaremych, a master's student in the
Department of Natural Resources and Environmental Sciences at the University
of Illinois in Urbana-Champaign, tracked 39 crows that were feeding and
roosting in an area where she also found infected mosquitoes. Yaremych
found that when the large birds became infected, they moved around less,
possibly making them more vulnerable to mosquitoes. The finding could explain
why large numbers of mosquitoes can become infected in areas with lots
- By last fall, at least 49 percent of Yaremych's crows
had died. Her study confirms evidence from around the state that populations
of birds, especially crows, jays and chickadees, have declined dramatically.
- "Basically what we found is that in the areas where
there were high numbers of human cases, the crows and chickadees were absolutely
missing," says Judy Pollock, Chicago region projects manager for the
National Audubon Society.
- Even as scientists scramble to evaluate data collected
from last summer, the new season of West Nile is upon us. In New York,
the second and third years of West Nile activity were not as bad as the
first, but last year, the fourth, the state had more human cases than ever,
despite improved surveillance and abatement efforts.
- "The status of the disease can change from year
to year, so making a prediction is really risky. Really risky," says
Lampman, who is investigating whether species besides Culex pipiens may
be infecting humans.
- Scientists agree that the virus is not going away, and
that people have to learn to deal with it, mainly by eliminating breeding
sites around their homes and protecting themselves with repellent.
- Many people in Cook County did not feel that last summer,
which was hot and dry, was a particularly bad summer for mosquitoes. That
is probably because there were fewer pesky Aedes vexans, the floodwater
mosquitoes that need rain for their developing eggs. But drought is good
for the Culex, because its eggs, laid in stagnant water, aren't washed
- "The throttle is heat," says Haramis, the IDPH
entomologist. "Not only do mosquitoes breed more quickly when it's
hot, but the virus replicates more quickly in the mosquito."
- Mild winters also favor the survival of hibernating mosquitoes,
so Haramis says that while things can change, it's a good early sign that
the recent winter's cold temperatures were near average.
- "I can make one prediction," says Nasci, of
the CDC. "Chicago will have West Nile virus activity this year. How
much? That's why the surveillance program is there. All of the programs
should be advised to prepare for a possible repeat of last year."
- Patricia A. Doyle, PhD
- Please visit my "Emerging Diseases" message
board at: http://www.clickitnews.com/ubbthreads/postlist.php?Cat=&Board=emergingdiseases
- Zhan le Devlesa tai sastimasa
- Go with God and in Good Health