Sierra Club fact
sheet on West Nile Virus

This fact sheet was written by the Northeast Ohio Group of the Sierra Club in April 2001.

Q: What is West Nile virus (WNV)?
A: West Nile virus is a mosquito-borne virus. Most people who are infected with WNV have no symptoms or experience mild illness, and recover completely without the need for medical care. Most mosquitoes are not infected with the WNV. Only one percent of the population bitten by an infected mosquito will have any symptoms, and of those, 1% may contract encephalitis, which can be fatal, particularly in elderly persons with compromised immune systems. This indicates that death from WNV is rare.

Q. Is the Cuyahoga County Health Department considering using agents to eradicate mosquitoes?
A. Yes. One of the agents is metheprene, a larvacide. This agent makes it impossible for insects to mature and reproduce and it has demonstrated no toxicity to mammals. Mosquitoes in the county are being monitored. If a mosquito tests positive for the WNV, trucks will transport pesticides throughout neighborhoods within the locale the mosquito was located, spraying synthetic pyrethroids. Synthetic pyrethroids are a class of insecticides which are an artificial imitation of the chrysanthemum. They are often combined with chemicals that are listed on the Toxic Release Inventory list to "carry" the active ingredient.

Q. Are these pesticides safe?
A. No. People naturally assume that pesticides undergo lengthy testing by the government before being cleared for use. However, the Environmental Protection Agency, the agency responsible for registering pesticides, admits that most pesticides sold today have not been adequately tested. It is illegal for a pesticide manufacturer or applicator to describe a synthetic pesticide as safe.

Q. Do pyrethroids kill most of the mosquitoes?
A. No, which is the most ironic aspect of the spray policy. If it did, the Earth, which has endured billions of tons of pesticide exposure, would already be mosquito-free. Pesticide spraying often results in new generations of pesticide resistant mosquitoes. Dr. David Pimentel, a noted entomologist from Cornell University, has repeatedly questioned the efficacy of spray-based strategy against mosquitoes. Dr. Michael Hansen, Senior Scientist at the Consumer's Union in NYC calls this spray policy "overkill." According to literature written by entomologists at Queen's University in Canada, "The sprays kill the mosquitoes ONLY within that area and ONLY at the time of the spraying. Reinvasion (of mosquitoes) of the treated area occurs rapidly - within hours."

Q. What are the health risks from exposure to pyrethroids?
A. Short term effects can be coughing, stuffy nose, itching, and watery eyes. Long term effects can include long-term neurological damage, endocrine disruption with possible proliferation of breast cancer cells, and immune system dysfunction. Damage from exposure would usually not be manifested until long after the itching, runny nose or coughing have stopped. By then, it would be difficult to link the connection between the symptoms and exposure. Children, seniors and people with asthma and/or immune system suppression are individuals at most at risk from exposure. There have been reports of children with pre-existing respiratory conditions experiencing acute and serious breathing difficulties from exposure to pyrethroids.

Q. Are there peer reviewed medical studies concerning these risks?
A. Yes! Due to space limitation, listed here are just a few of the many sources.

  • Neurotoxicology, 1997;18(3):719-26. This study, conducted by the Department of Environmental Toxicology at Uppsala University in Sweden, found that low-dose exposure to pyrethroids resulted in irreversible changes in adult brain function in the mouse when exposed during the growth period.
  • Journal of Steroid Biochemistry, March 1990, volume 35, issue 3-4, pages 409-414. This study on pyrethroids, done at Brown University's Roger Williams General Hospital, concluded "Chronic exposure of humans or animals to pesticides containing these compounds may result in disturbances in endocrine effects." (There is strong evidence that links endocrine system dysfunction with breast cancer, by mimicking the effects of the female hormone estrogen.)
  • Journal of Applied Toxicology, vol. 16, no. 5, pages 397-400, 1996. This study revealed that laboratory exposure to pyrethroid insecticides for a relatively short time can suppress thyroid secretory activity in young adult rats.

(for more sources, see Beyond Pesticides and Northwest Coalition for Alternatives to Pesticides )

Q: Are there safer alternatives to deal with mosquitoes?
A. Yes. Eliminate any standing water that collects on your property. Wear a nontoxic insect repellent. Install bat houses in your backyard. Bats are nature's way of keeping the mosquito population down. The U.S. Coast Guard uses a mosquito abatement system in their tropical bases whereby a stream of carbon dioxide is emitted which pests mistake for the exhaled breathe of their prey. The mosquitoes are then lured into a net where they dehydrate and die within 24 hours. This mosquito abatement system is being sold commercially. (For more information, visit Mosquito Barrier.)

Q. Is it worth the risk to spray communities with synthetic pesticides to deal with WNV?
A. No. It is true that some mosquitoes carrying diseases may be in NE Ohio. However, there's no good research or proof of the efficacy of spray-based strategy against mosquitoes. It's also ironic to broadcast pesticides, such as pyrethroids, which kill birds, fish, and beneficial insects (such as bees and butterflies) - which help to keep the ecosystem in balance! What is needed is mass education. People should be instructed how to reduce exposure to mosquitoes, such as eliminating free standing sources of water on their property.

Let's look at the big picture. Is it worth introducing an agent into the environment that can cause irreversible health dysfunction to people and disrupt natural predator/prey systems, when the incidence of mortality from infection with West Nile Virus is negligible? The risk/benefit analysis clearly indicates that the dangers of WNV are minimal and affect a very small segment of the population. In comparison, long-term health and environmental risks of spraying with synthetic pesticides poses a much greater risk. As global warming progresses, scientists predict that mosquitoes carrying more deadly diseases, such as malaria and dengue fever, will proliferate. When pesticides are used unnecessarily, mosquitoes will have become resistant, and these chemical eradication controls will no longer be effective.

Conditions for the emergency application of broadcast spraying of pesticides to control WNV outbreak:

  • Evidence from biological surveillance using appropriate indicator species that a reasonable probability exists there will be a West Nile Virus epidemic in the human population for a particular geographical area.
  • All non-broadcast spray alternatives that have been used have not succeeded in preventing the likelihood of a human epidemic.
  • There is evidence that broadcast spraying in the city/town in question is likely to prevent or mitigate a human epidemic of West Nile Virus.
  • There is a program in place for pre-spray health-risk communications and warnings that can be implemented well in advance of any plan for broadcast spraying. Special considerations should be given to populations sensitive to pesticide exposure (children, pregnant women, chemically-sensitive individuals, and immunodeficient individuals).


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EcoCity Cleveland
2841 Scarborough Road Cleveland Heights OH 44118
Cuyahoga Bioregion
(216) 932-3007
Copyright 2002-2003

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