Spring 2003

The Great Spray Debate
Could synthetic sprays eliminate our best defense
against West Nile virus — a healthy ecosystem?

by Arthur Melvile Pearson

I live in the historic Pullman community on Chicago's Far South Side, located within one of the West Nile virus "hot spots" this past summer. My four nearest neighbors are Elvira, Julia, Emma, and Florence. They range in age from 75 to 94. I love each of these Italian widows as if they were my own family. So, with Illinois leading the nation in deaths resulting from the mosquito-borne virus and the median age of its victims hovering around 78, wasn't it the best decision for City of Chicago contractors to rumble their trucks down our back alley spraying for the potentially deadly adult mosquitoes?

No one knows how West Nile virus — first isolated in Uganda, Africa, in 1937 — showed up in a dead crow in New York's Bronx Zoo in August of 1999. And most experts are amazed that within just three years, the virus has fatally infected a staggering number of birds, horses, small mammals, and people in 43 states, the District of Columbia, and five Canadian provinces. As of the end of 2002, there were 3,873 human cases of West Nile virus-associated illnesses reported nationwide. Two hundred and forty-six persons died, the majority from West Nile meningoencephalitis. Fifty-two of the deaths were in Illinois.

The two Illinois hot spots — clusters of West Nile virus human cases — were a 72-square-mile city-suburban area on the north side of Chicago, and a 215-square-mile city-suburban area on the south side. In accordance with recommendations from the Illinois Department of Public Health and the Centers for Disease Control and Prevention (CDC), many communities and mosquito abatement districts within these two areas resorted to fogging or aerial spraying. Yet even communities where infection rates were minimal elected to spray. Franklin Park, which had banned spraying since 1970 believing that "adding toxic chemicals to the environment...could endanger the animal life including humans," decided to spray with only a single human case being reported within its borders.

Anvil is the commercial name for the synthetic pyrethrin insecticide used by Chicago and many of the region's communities and mosquito abatement districts. It kills upon contact every mosquito that it touches. But what about those mosquitoes that avoid the spray by lodging under leaves or behind tree bark, or simply escape the spray drift behind a garage or due to a shift in the wind? In its own press release, the City of Chicago acknowledges that spraying may have reduced the number of adult mosquitoes in targeted areas by 50 percent. However, while such a treatment may reduce numbers for a few days, the Illinois Department of Public Health admits that it does not prohibit more mosquitoes from entering the area.

Dr. William Paul, deputy commissioner of the Chicago Department of Public Health, acknowledges that spraying of adult mosquitoes is the least effective means of mosquito control. "Our earliest efforts were to attack mosquitoes at the larval stage, but when you reach a point where there are infected adult mosquitoes biting people, the only thing to do is kill them as adults. In an extraordinary outbreak situation like 2002, spraying does have a role."

Not if Barbara Mullarkey has anything to say about it. When the Village of Oak Park announced that it would spray for mosquitoes last summer, she resurrected the dormant Oak Park Environmental Network (OPEN). In the early 1980s, OPEN played a pivotal role in urging the Oak Park Village Board to pass an ordinance that strictly regulated the use of synthetic pesticides in the village. But when the village, which had not sprayed for mosquitoes since 1983, gave notice of the planned spraying in the local paper, Mullarkey wrote to the press, circulated petitions, and — armed with 40 supporters, some wearing gas masks, some carrying placards — showed up with a bullhorn in front of village hall. At a later board meeting, the debate went back and forth. Those against spraying argued that pesticides were poisons and lamented the lack of public debate. Those who favored spraying accused the protestors of stirring up "mass hysteria" and cited U.S. Environmental Protection Agency (EPA) approval of Anvil.

On August 19, the entire village was sprayed. A second spraying slated for September was delayed due to unfavorable weather conditions. The cooling temperatures thereafter began to limit populations of mosquitoes naturally, rendering a second spraying unnecessary in Oak Park. But Chicago sprayed again. On September 17, the city contractors from Clarke Environmental Mosquito Management hit the northwest and southwest sides a second time. Although "the number of infected mosquitoes was on its way down," due to weather and the time of the year, Deputy Commissioner Paul claimed that "we wanted to accelerate the decline of risk."

But what, exactly, is the degree of risk? Chicago's Web site carries the message that, even where West Nile is established, fewer than one percent of mosquitoes are infected. The CDC estimates that the majority of people who become infected will experience no symptoms at all. Twenty percent may develop West Nile Fever, with flu-like symptoms that may last a few days. The CDC further estimates that only 1 in 150 infected individuals, or .7 percent, may develop a more severe manifestation of the disease.

Compared to the low risk of contracting this serious disease, what is the likelihood of someone suffering a reaction to the spraying itself? According to the National Pesticide Information Center, inhaling pyrethroids — if you happened to be outdoors during spraying, for instance — can cause its own flu-like symptoms: "coughing, wheezing, shortness of breath, runny or stuffy nose, chest pain, or difficulty breathing...rash, itching, or blisters." Those most at risk are the young, the elderly, those with asthma, and those with chemical sensitivity.

As for long-term risks, the EPA has determined that pyrethroids are carcinogenic, although which risk classification remains to be determined. The No Spray Coalition reports that the various elements in Anvil are either known or suspected to be toxic to the liver, kidneys, the gastrointestinal tract, and the respiratory tract.

Proponents of spraying point out, however, that the risks associated with pyrethroids depend on the amount and the length and frequency of exposure. According to the EPA, the amount of pyrethroids used to control mosquitoes is less than four fluid ounces per acre. This low concentration, combined with the infrequent number of applications and the relative instability of pyrethroids (they have a soil half-life of only 12 days and they do not easily migrate into groundwater or waterways) led the EPA to classify pyrethroids as being of low toxicity to humans and other mammals.

But not to other creatures. Pyrethroids are toxic to a range of beneficial insects including honeybees. They are also toxic to many species of aquatic insects and highly toxic to tadpoles and fish, which is why spraying within 100 feet of a water body is prohibited. Deputy Commissioner Paul was not aware of any reports of massive die-offs of nontarget species — but not being required, the agency conducted no ecological monitoring.

And what about birds, which were the bellwether species for the virus this past summer? The virus itself appears to have taken a large toll. This past July, several members of the Bird Conservation Network — a corps of 210 volunteers who monitor bird populations throughout the Chicago Wilderness region — began reporting a suspicious absence of American crows and chickadees. Judy Pollock, bird conservation projects manager for Audubon-Chicago Region, coordinated an immediate volunteer survey.

	Human cases sources: Illinois Department of Public Health Chickadee sightings source: Audubon-Chicago Region

The results were alarming. Survey teams recorded sightings of just three crows in all of Chicago's northern suburbs and the far north and northwest sides of Chicago. Usually ubiquitous crows were astonishingly fewer in numbers in all or significant portions of Cook and DuPage Counties. Chickadees, another common bird of the cities and suburbs, were nearly completely absent from some south suburbs and a large swath of northern Chicago and adjacent suburbs. Monitors observed dead or obviously diseased birds, including American kestrels, great horned owls, red-tailed hawks, blue jays, house sparrows, house finches, and even pigeons. In late December, the annual Christmas Bird Count reported bird declines reaching 80 percent for the hardest-hit species. Nationwide to date, West Nile virus has been detected in 138 bird species, from endangered black-crowned night-herons to domestic chickens.

But Pollock and other conservationists are also concerned about the effects spraying adulticides might have on bird populations. According to the National Pesticide Information Center, pyrethroids are only "slightly toxic" to birds. But as Carolee Caffrey, science associate with the National Audubon Science Center observes, "We don't yet have enough data, but if you spray toxins on the food a bird eats, in the air it breathes, you're possibly further stressing an already greatly stressed creature, making it even more susceptible to West Nile and other diseases. I'm worried that spraying adulticides on top of all the other stress factors — disease, pollution, habitat loss — could push some endangered and threatened species over the brink."

Even though the Illinois Department of Public Health began preparing for the onset of West Nile virus in 2001, no one was prepared for its virulence. "To have expected public agencies to have arrived at a well-considered solution was unrealistic," admits John Rogner, Fish and Wildlife Service field supervisor for this region. "But now that winter gives us a brief respite from the disease, we can pull together the best information available." Although much remains to be learned, several authorities assert that our best weapon for defending human health against West Nile virus and related diseases is to understand and defend our ecosystems.

Dr. Robert J. Novak, professional scientist for the Center for Economic Entomology at the Illinois Natural History Survey, notes that many of the nontarget species likely to be impacted by spraying are0 mosquito predators.

Some species of fish and aquatic insects eat mosquito larvae. Dragonflies feast on adult mosquitoes, and birds and bats eat a wide range of insects that may be sprayed.

If significantly reduced — either by the direct effects of spraying or by stress and starvation because their food source has been disrupted — populations of these mosquito predators do not typically recover as quickly as their prey. This can result in an even greater, naturally unchecked surge in the number of mosquitoes. Such a surge could trigger decisions to spray even more, further compromising nature's ability to regulate itself, leading to more mosquitoes, leading to more spraying, and so on.

Dr. Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School, acknowledges that once we know enough about West Nile virus and the impact of various treatments on our ecosystem, we may need to resort to the use of synthetic pesticides such as pyrethroids. But there is much we don't understand. Epstein worries that the "ecological ripples" that could follow the disruption of nontarget species may ultimately affect humans. In general, he argues that rather than willfully disrupting the natural regulatory mechanisms inherent in nature, the best way to protect human health is to pursue a stable, balanced ecosystem.

Last spring, government agencies sprayed for gypsy moths and likely killed off a whole host of caterpillar species (see Gypsy Moths to Be Sprayed Again). This past fall, other government agencies fogged for mosquitoes. The stressed ecosystem, already reeling from pollution and habitat loss among other things, could lose yet more of its ability to regulate itself just as an overweight, habitual smoker is likely to end up very sick with whatever disease drifts along.

Everyone interviewed for this article — public health officials included — agreed that the most effective way to control mosquito populations is during their larval stage, when mosquitoes are "C.I.A." — Concentrated, Immobile, and Accessible. Dr. Novak, who coined the acronym, explains that even in complex wetland areas, mosquito larvae generally are concentrated in identifiable pockets (often less than one percent of the total water surface). Treatment, therefore, may be narrowly targeted, resulting in the greatest degree of control effectiveness with the fewest nontarget effects.

As part of its overall Integrated Pest Management strategy, the City of Chicago dropped larvicidal pellets into 210,000 of its catch basins, which are notorious breeding sites for the Culex family of mosquitoes, known carriers of West Nile virus. The city used the synthetic larvicide methoprene, rather than equally effective natural biological controls such as Bacillus thuringiensis israelis (Bti). (For those who follow the gypsy moth spray debate, another variety of Bt, Bacillus thuringiensis kurstaki (Btk) is criticized for use against gypsy moth caterpillars because it indiscriminately kills many other varieties of caterpillars. However, Bti is relatively species-specific, fatal only to mosquito and black fly larvae.)

To its credit, the city did apply the environmentally friendly biological larvicide Bacillus sphericus to lagoons in nine city parks, and intends to do the same this coming mosquito season. However, its plan to continue to use synthetic larvicides and adulticides remains a serious concern. The Villages of Oak Park and Franklin Park also have left open the door to use synthetic sprays if deemed necessary next year.

Steve Messerli, executive director of the Lake County Forest Preserves, doesn't anticipate that his agency will be spraying district lands in 2003. They didn't last year in spite of the presence of infected adult mosquitoes. "Our concern about spraying is the effect it might have on other forms of wildlife," says Messerli. He plans to determine the most effective control strategies by convening a Mosquito Management Technical Advisory Committee that will include a representative from the U.S. Fish and Wildlife Service, the Lake County Health Department, the Chicago Botanic Garden, and even Clarke Environmental Mosquito Management, the region's primary contractor for synthetic spraying.

If there is a silver lining to the West Nile virus epidemic, it is the way it is encouraging just this kind of discussion toward an interdisciplinary approach to health. As Mark Jerome Walters, D.V.M., also of the Center for Health and the Global Environment, observes, "[the concept of] ecological health views human health as an extension of healthy natural systems, not separate from them." Everything we eat and drink and breathe is part of global and regional ecosystems. What we do to the least of nature's creatures, we ultimately do to ourselves. The fewer poisons, the stronger our natural systems, the safer for everyone.

Arthur Melville Pearson is a freelance writer currently at work on a biography of George Fell, co-founder of The Nature Conservancy and founder of the Natural Land Institute.