West Nile Virus: How Vulnerable Are We?

Posted: 14-Aug-2002; Updated: 06-Feb-2007

In the three years since the West Nile virus was first detected in the United States (in the New York City area in 1999), the virus has spread to 34 states and the District of Columbia and has been reported in Canada, sickening more than 200 people and causing more than 20 deaths. Four people have died recently from the disease in Louisiana (where the mosquito is jokingly called the state bird), prompting Governor Mike Foster to declare a state of emergency. With the advance of summer, more outbreaks are expected as the mosquito-borne virus takes on epidemic proportions.

Just how deadly is the West Nile virus and how worried should we be? Says Dr. John Balbus, Director of the Health Program at Environmental Defense: "Compared to HIV, Ebola or some other virus out of a horror movie, West Nile virus isn't so bad But it is very widespread, and any disease that kills people is a serious and significant public health threat, particularly in the United States where we don't face a bewildering array of deadly infectious diseases."

The chances that you will become severely ill from a mosquito bite are extremely small. According to the Centers for Disease Control, even in areas where the virus is circulating, very few mosquitoes are infected with the virus. (Mosquitoes get the virus through feeding on infected birds. Infected mosquitoes may then transmit the virus to humans through bites.) Less than one in a hundred humans who get bitten by an infected mosquito and get the virus will develop more serious illnesses like meningitis or encephalitis (most who contract the disease get mild, flu-like symptoms). And for those who do get seriously ill, death rates range from 3% to 15% and are highest among the elderly (those over age 50). The virus cannot be transmitted from person to person.

What does worry experts is that this year's outbreak occurred earlier in the mosquito season -- the first case erupted in June. And while the mosquito-breeding season normally lasts through September in temperate areas, in the milder-climed southern United States it can stretch through winter -- giving more time for mosquitoes to proliferate and transmit the virus. Dr. Balbus stresses that "non-chemical measures should certainly be employed first to combat mosquito infestation. People should reduce breeding sites in their yards and take other precautionary measures to avoid getting bitten by mosquitoes -- although people should also keep in mind that applying the insect repellent DEET has its own risks, particularly neurotoxicity in children." Balbus cautions that prudence and common sense should be used when it comes to DEET, applying it sparingly and as infrequently as possible: "follow the guidelines, avoid putting it on children under the age of 2, and keep the concentration under 10 percent in children over 2."

And what about chemical means to eradicate these insects? In some areas where mosquitoes are rampant, officials are routinely spraying pesticides -- sometimes heavily. In Baton Rouge and New Orleans, trucks are reportedly spraying twice nightly. According to The Atlanta-Journal Constitution, in St. Tammany "trucks and planes are constantly loading up with pesticides to spray throughout the parish," and The Times-Picayune says the parish is "spraying more pesticide in a single night than it usually does in a week." Grand Forks, North Dakota, is being blanketed with the pesticide Trumpet (see below).

Not everyone is happy about the spraying of chemicals. Complaints have come from residents of Winnipeg, Canada, over the city's pesticide spraying to exterminate mosquitoes, saying it is causing respiratory problems. And central Texas residents rose up in arms over proposed insecticide spraying over a wide area and succeeded in limiting spraying to only vicinities where residents were in consent and where health officials deemed it absolutely necessary.

Swatting mosquitoes with a sledgehammer?
But is such spraying of pesticides warranted and safe? "Anytime you have a disease spreading that kills people, fairly aggressive control measures are appropriate," says Dr. Balbus. "That said, the selection and use of chemical pesticides needs to be prudent and thoughtful."

The pesticides registered for use to control adult mosquitoes and combat an outbreak of mosquito-borne disease (called adulticides) are, according to the Environmental Protection Agency, applied either by aircraft or on the ground employing truck-mounted sprayers. State and local agencies commonly use the organophosphate insecticides malathion and naled and the synthetic pyrethroid insecticides permethrin, resmethrin, and sumithrin.

Pyrethroids are synthetic compounds similar to pyrethrum (the natural insecticide in chrysanthumums). Sumithrin is the active ingredient in Anvil (which has been recently sprayed in Brooklyn and Staten Island) and permethrin is the active ingredient in such brand names as Aqua Reslin, Biomist and Mosquito Beater. While permethrins are considered not especially toxic to mammals, they are considered more so to bees and other insects (including of course mosquitoes) and to fish. Says Dr. Balbus, "malathion and naled are more acutely toxic alternatives to permethrins."

Although organophosphates (malathion and naled) are considered to be more toxic, EPA's risk assessments of all these pesticides say that, if used strictly according to label directions for mosquito control, they pose no unreasonable risks to the general population or to the environment. Naled is being used for aerial spraying in East Baton Rouge, according to officials at the Mosquito Control Division there and (resmethrin for ground spraying from trucks -- the Extension Toxicology Network lists resmethrin as "a slightly to practically non-toxic compound" but says the chemical may be toxic to fish). Trumpet (sprayed in Grand Forks) is the brand name of an organophosphate whose active ingredient is naled.

A cure worse than the disease?
The main immediate danger from pesticide spraying comes from inhaling the solvents and other chemicals used as "vehicles" for the active pesticide ingredients, putting those with asthma and other respiratory problems at particular risk. And swallowing pesticides-- either accidentally or intentionally -- could result in serious organ or brain damage. (For example, Scorecard lists sumithrin as a suspected gastrointestinal or liver toxicant, kidney toxicant and neurotoxicant.)

Repeated long-term exposure to pesticides has been linked to certain cancers and neurological problems in agricultural workers, who spend long hours day after day working in fields sprayed with pesticides. Because average citizens are exposed to much lower levels, the risks from long-term repeated exposure are less well understood, says Dr. Balbus.

As for repeated nighttime spraying, Dr. Balbus comments that "spraying at night does tend to minimize exposure -- the risk of inhaling the pesticide is highest if you're outside while the spraying is occurring." While organophosphates usually don't stick around more than one or two days in an area, that is enough time for some exposure to occur from the residues on plants and trees. "Again, it's a matter of prudence and common sense. I would certainly not allow children -- who are more vulnerable to the effects of exposure to pesticides -- to play on the grass or in trees the morning after spraying in the neighborhood."

Also, keeping abreast of local announcements of when spraying will occur and then staying indoors with windows closed is a wise course of action, says Dr. Balbus. "Under no circumstances should children ever be outside or allowed to play near a spraying truck. Bring in pets as well and remove pet food and dishes from outdoor areas. If officials in your area are lax about alerting the public about spraying or possible hazards, put pressure on them to do that."

Overall, Dr. Balbus cautions that city and county officials should ensure the careful application and careful adherence to existing guidance on the use of these pesticides. "While we recognize the need to protect human life, we also need to recognize that these pesticides can be toxic to animals, to beneficial insects and to humans, and we need to use them in the minimum amounts necessary for success."

"The West Nile virus is going to be with us for the foreseeable future and will spread," explains Dr. Balbus. "We need to make sure we have a comprehensive, coordinated program to control this disease.  But since most of the infections do not lead to significant illness in humans, we need to make sure that our cure isn't worse than the disease itself."

By Leslie Valentine

Quick Tips: What You Can do to Protect You and Your Family

FIND OUT MORE
Frequently Asked Questions on West Nile Virus (CDC)
General information on pesticides and mosquito control (EPA)
How the virus is transmitted (CDC)

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More on Pesticides From Scorecard
Pyrethroids