Understanding the balance being struck between the respective public health risks of a mosquito-borne virus, now believed to be the West Nile virus, and the emergency response — widespread spraying of pesticides — requires a complete accounting of the hazards of both. The pesticides being used cannot be characterized as harmless, and their risks must be fully communicated to the public in order to ensure that New Yorkers take all available precautions to minimize their exposure. Failing to disclose such risks may promote an unwarranted level of comfort with blanket spraying as a pest management method, forestalling the necessary implementation of safer, preventative methods of mosquito larvae control, surveillance, and targeted response.

The recent outbreak of this mosquito-borne virus, which has already claimed lives in New York, clearly must be addressed. But widespread and repeated pesticide spraying, independent of evidence that infected mosquitoes are present or active in significant numbers in the sprayed area is not a neutral undertaking. It is essential that public health officials institute coordinated mosquito management practices that better anticipate disease outbreaks before people become infected, and thereby prevent or minimize the need for such dramatic measures in the future.

• Accurate and precise advance warning to residents prior to spraying in their neighborhoods, accompanied by materials describing the health effects of the pesticide being sprayed and necessary precautions people can take to minimize their pesticide exposure. Information should be available in both English and Spanish, as well as in other languages in neighborhoods where those languages are spoken.
• Maximum implementation of targeted larval control measures to reduce the need for blanket spraying of adulticides this season.
• City and County Health Departments to track reports of adverse health effects in the wake of spraying, through poison control centers, clinics and emergency rooms.
• Public hearings to review state and local government response to the current outbreak, including systems for notifying people of spraying, future surveillance plans to detect possible disease outbreaks, and alternative mosquito control efforts, using preventative, least toxic management approaches.
• In New York City and other municipalities that do not currently have them, the establishment of Pest Management Boards to take a comprehensive look at all of the municipality’s pest problems and devise preventative, least toxic management approaches to them. These Boards should include local residents, public health and environmental interest groups, physicians, scientists, and municipal leaders.
• Coordination among state and local public health officials in the tri-state New York City metropolitan area with regard to improved surveillance, control measures, and emergency response planning.

For discussion and information purposes, the following are capsule descriptions of the insecticides malathion, resmethrin, and sumithrin which are currently being deployed, and alternative methods for managing the particular mosquito species believed to carry the disease.

Infants and children, whose immature nervous systems are more vulnerable to insult, and newborns, whose metabolisms are less capable of detoxifying malathion, are more susceptible than adults to its toxic effects.⁴ Organophosphate poisoning in children may also result in a different, and therefore less readily recognized, set of symptoms than adults commonly experience, including increased muscle tension and rigidity. ⁵

Information on long-term, chronic effects is less abundant than for acute poisoning. Currently, malathion has not yet been classified by the United States Environmental Protection Agency (EPA) as to its carcinogenic potential, although a decision on its classification is pending.⁶ Over the years, reports in the epidemiological literature have indicated that malathion may compromise the immune system⁷, cause reproductive harm,⁸ and cause genetic mutations or interfere with normal cell replication.⁹

How these reports of possible chronic health problems may relate to the level or frequency of exposure encountered in the current New York City spraying campaign is unknown. It is also impossible to say how malathion may interact with the other pesticides to which City residents are exposed. Data on such chemical interactions are virtually nonexistent.

Being a broad spectrum insecticide, malathion kills other insects as well as mosquitoes, including honeybees, to which it is highly toxic. It is also highly toxic to many aquatic organisms and the aquatic life cycle stages of amphibians.¹⁰

Resmethrin and Sumithrin

Resmethrin and sumithrin (also called d-phenothrin) are synthetic pyrethroid insecticides. Pyrethroids, like organophosphates, affect the nervous system, though they do not inhibit cholinesterase. They are of relatively low acute toxicity, although poisoning can occur and allergic responses have been reported.¹¹ There are also reports of persistent symptoms when exposures occurred indoors.¹²

Resmethrin is the active ingredient in Scourge, which is being sprayed from trucks. Sumithrin is the active ingredient in Anvil, which is being used for aerial applications.

Like malathion, resmethrin and sumithrin have not yet been classified with regard to carcinogenicity, although products that contain these substances often include the synergist piperonyl butoxide (PBO), which has been classified by the EPA as a possible human carcinogen, as have several other pyrethroid insecticides.¹³ There are some indications that pyrethroids as a class may interfere with the immune¹⁴ and endocrine systems.¹⁵ Other adverse chronic effects, including effects on the liver and thyroid, have been reported in toxicology testing of resmethrin.¹⁶

Again, as with malathion, conclusions regarding the possible risk of chronic effects at the level and frequency of exposure occurring as a result of the widespread spraying campaigns now underway, and chemical interactions with other pesticides, cannot be drawn.

Resmethrin and sumithrin are highly toxic to bees, and resmethrin is also toxic to fish.¹⁷¹⁸

Preventative and Least-Toxic Mosquito Control

The species of insect believed primarily responsible for transferring the West Nile virus to humans in the New York City area is Culex pipiens. This light brown mosquito feeds (by biting) primarily on birds, where it can pick up the virus, but will also feed on other hosts such as humans and other mammals.¹⁹ Their flight activity and feeding times are generally restricted to periods of darkness, with the highest level of feeding activity occurring at dawn and dusk.²⁰ During the day, adults reside in dark, damp areas, such as storm sewers and culverts.²¹  Because they may get trapped in houses, screens on windows and doors are important protective measures. Culex is a hardy mosquito, common in urban areas, that breeds in polluted water high in organic content, such as storm sewers and sewage treatment effluent.²²

Controlling Culex populations with adulticides such as malathion, is a strategy of last resort, when all other control possibilities have been exhausted and a public health emergency requires action. It should not be the first or only line of defense. In addition to health concerns about pesticides, repeated use of these chemicals breeds resistance and reduces their effectiveness for times when they may be the only option. Houston authorities, for example, do not use malathion for mosquito control because the Culex populations there have developed a resistance to it,²³ and Los Angeles authorities have become concerned about a similar upswing in resistance in that area.²⁴ There may also be unintended effects from spraying: Dr. Ray Parsons, who heads the Harris County Mosquito Control Division in Houston, has observed that malathion may actually aggravate Culex, causing an increase in aggressive biting behavior for an hour or two after spraying. ²⁵

There are many more effective options for preventing and controlling future potential mosquito-borne disease outbreaks that minimize the use of hazardous pesticides. Preventative mosquito control relies on a combination of before-the-fact measures, including:

• Removal of breeding habitat by reducing standing water wherever possible.²⁶
• The use of meteorologic data to identify weather patterns known to exacerbate specific vector-borne diseases and follow up with enhanced monitoring when such conditions exist.²⁷
• Control of mosquito populations when they are in the larval and pupal stages. There are a variety of non-toxic and least toxic methods of larval control, such as applying bacillus thuringiensis israelensis (BTI) bacteria to stagnant waters, bacillus sphaericus to storm sewers, and stocking isolated water bodies with mosquito-eating fish. Some of these products have effects on non-target species and thus each use should be evaluated from this perspective.²⁸
• Trapping and monitoring mosquitoes to detect the presence of mosquito-borne illnesses. Trapping not only indicates the presence or absence of disease, but can localize the source of infectious agent so that targeted responses with least-toxic insecticides can be implemented, instead of blanket spraying of wide areas. In addition to monitoring, new traps are on the market, using carbon dioxide as a lure, which are designed to control mosquito populations for areas of up to an acre.
• The use of sentinel birds to detect the presence of disease before it reaches humans. For instance, chickens are commonly used bird hosts for monitoring whether St. Louis encephalitis is present in the local bird population. Like trapping and monitoring of mosquitoes, sentinels detect the presence of disease before it reaches human populations and help to locate the areas where it must be controlled.²⁹

The benefits of preventive control and monitoring are myriad. They reduce the likelihood that a surprise outbreak will occur while minimizing the use of hazardous pesticides. Harris County (Houston), which has one of the most active St. Louis encephalitis programs in the country, has not conducted aerial spraying for years. Through effective monitoring, their program can identify infected areas a month before any human comes down with the virus, and thereby address potential outbreaks at the source. This approach not only saves human lives, but also reduces pesticide use and saves the county approximately one million dollars each year.³⁰

Unfortunately, there are no perfect ways to prevent pesticide exposure given the nature of its widescale application, but you can take some common-sense precautions to minimize it:

• Keep windows shut and air conditioners off during and after spraying for as long as possible.
• Bring pet dishes, toys, laundry, and other portable objects inside.
• Cover outdoor furniture, barbecue grills, sandboxes, and play equipment, and rinse off surfaces that cannot be covered before use.
• If you get directly sprayed, shower immediately. If you believe that you are experiencing symptoms as a result of pesticide exposure, call your doctor or your local poison control center.

To reduce your exposure to mosquitoes:

• Repair or install window and door screens to keep mosquitoes from getting into your home.
• Drain standing water around your home and yard where mosquitoes can breed, by cleaning roof gutters, removing old tires, buckets, and other traps for water, and regularly changing the water in wading pools.
• Wear non-toxic insect repellent and protective clothing outdoors during mosquito season, especially between dusk and dawn when mosquitoes are most active.

You can also let the County Executive and your County Legislator know that you are concerned about this kind of stop-gap deployment of chemicals and that you would like to see preventative pest control policies instituted to preclude the need for such action in the future. In New York City, contact the Mayor and your City Councilperson.

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