PANUPS: Keeping Perspective on West Nile Virus

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Mon, 22 Aug 2005 23:24:38 GMT

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PANUPS: Keeping Perspective on West Nile Virus

 

 

 

 

Keeping Perspective on West Nile Virus

August 22, 2005

 

As the West Nile Virus (WNv) has moved across the U.S., a number of

communities have responded to the threat of illness and officials'

plans by joining coalitions against pesticide spraying. Until

recently, the U.S. Centers for Disease Control and Prevention (CDC)

and many local mosquito abatement districts emphasized public

education and the control of larval populations as the first line of

defense against the virus. But as current experience in the California

Central Valley shows, spraying of hazardous pesticides to kill adult

mosquitoes is still being used as a primary WNv control mechanism. In

these cases, community members are forced to scramble as spray

programs are hastily implemented. Local groups need better information

if they are to decide if the plans of their local public health and

mosquito abatement authorities are truly in the best interests of the

health and wellbeing of their communities. Unfortunately that

information is not coming from the CDC, and what is offered is highly

arguable.

 

There are a few key facts about the virus and its control. First, CDC

estimates that 80% of those infected never show any symptoms. Twenty

percent will develop West Nile Fever with flu-like symptoms such as a

headache, fever, and muscle aches, but fewer than one percent of those

infected will develop the West Nile Neuro Invasive Disease, which can

cause inflammation of the brain and spinal cord, and can be life

threatening. Those at highest risk for serious illness are the elderly

and people who have weakened immune systems.

 

Second, the most effective virus prevention involves personal

protection and control of larval populations (occurring in ponds or

other stagnant water sources) rather than the use of pesticides

against adult mosquitoes. Effective public health strategies have

focused on educating the public on how to help eliminate mosquito

breeding grounds (eliminate standing water nearby) and how to reduce

exposure to insects by wearing sensible clothing (e.g., long-sleeve

shirts), limiting outdoor activity at certain times and by using

insect repellents. (Many repellents are available; Pesticide Action

Network North America recommends those not containing DEET

[N,N-diethyl-meta-toluamide]. See " Ways to Beat DEET " on the PANNA

website

[http://www.panna.org/resources/documents/waysToBeatDEET.dv.html ].

Pesticide treatments for larval control involve much smaller

quantities of pesticides with fewer known health effects than those

used against adult populations.

 

In a troubling turn away from the emphasis on larval treatment, public

health authorities in some California counties are increasingly using

adulticides, arguing that ultra low volume sprays result in no

substantial (our emphasis) human exposure. While there is some recent

evidence that adulticide applications may decrease mosquito

populations, there is still no clear evidence of decreased incidence

of West Nile Neuro Invasive Disease. In fact, a survey by a Nashville

No Spray Coalition notes that some communities that have not used

adulticides as part of their mosquito control programs have reported

no significant difference in number of WNv cases compared to cities

and counties that have used adulticides.

 

The main pesticides used against adult mosquitoes are organophosphate

pesticides such as naled or malathion, and pyrethroid pesticides

including permethrin and d-phenothrin (Anvil). Organophosphates are

nervous systems toxins; both naled and malathion have been linked to

cancer and malathion has been associated with blood, vision and

reproductive disorders. Synthetic pyrethroids can cause dermatitis and

asthma-like reactions, are suspected disruptors of human hormone

function and possible carcinogens. These pesticides may be sprayed

alone, in combinations with one another, or together with " inert

ingredients " such as the synergist piperonyl butoxide (a possible

carcinogen).

 

A recent report cited in support of the " no substantial exposure "

argument appeared in the June 3, 2005 issue of Morbidity and Mortality

Weekly Report of the CDC. The CDC claimed that the levels of naled,

permethrin, and d-phenothrin detected in small samples from the three

states of Mississippi, North Carolina and Virginia (sample size of

exposed individuals were 125, 75 and 83 respectively) " might be too

low to cause important human exposure. "

 

However, the data do not support this claim for several reasons.

First, a lack of difference between exposed and unexposed individuals

may simply result from having sample sizes that are too small to

detect differences. When variation in pesticide exposure is

substantial among individuals in a population (for example, the

subjects in Mississippi who treated pets with permethrin had much

higher levels of the permethrin metabolite, 3-phenoxybenzoic acid,

than those who did not), then much larger samples sizes are needed to

determine whether differences between " exposed " and " unexposed " groups

exist. In the North Carolina study, for example, food was found to be

a substantial source of naled metabolite (DMP). By comparison, the

CDC's 2001/2002 study of chemical exposure in the U.S. population

tested more than 2,500 individuals for pesticides in their urine and

had sample sizes for different compared groups ranging from 500 to

1300 individuals.

 

Second, the levels of 3-phenoxybenzoic acid (3pba) in the Mississippi

study were about four times higher than the average levels measured by

the CDC in their 2001/2002 study. The notably high levels in these

communities may mask any differences due to spraying. One should ask,

" Why is everyone so highly exposed in the Mississippi study? "

Similarly, the 3pba post-spray levels in the Virginia study were

double the values in the CDC national study.

 

Third, and perhaps most importantly, no one can claim that application

of these pesticides " is safe. " The known health effects of these

pesticides are enough to negate that claim. Furthermore, full

information on the health effects of these pesticides is unknown. The

pesticides in question have not yet been evaluated for several chronic

or long-term health effects. No information is available on whether

naled can impact the human hormone system. Permethrin and d-phenothrin

have yet to be evaluated regarding their toxic effects on reproduction

and development. We know that the pesticide synergist piperonyl

butoxide is listed as a possible carcinogen, but it has yet to be

evaluated regarding its effects on human development or on human

hormonal or reproductive systems. Furthermore, in the real world we

are never exposed to single pesticides alone. We know virtually

nothing about the health impacts of either these chemicals together or

of these chemicals in combination of the myriad chemicals we already

carry in our bodies.

 

In the light of the many unknown risks of these hazardous pesticides,

activists are working in many U.S. communities to protect the public

and the environment from unnecessary exposure. The National Alliance

for Informed Mosquito Management (AIMM) represents more than 30

organizations and individuals promoting safer, least-toxic methods of

managing mosquitoes. Community activists have successfully worked with

local mosquito control boards to suspend aerial spraying and to

implement safer control methods. Often mosquito control boards will

provide the options for residents to join " no spray " lists that may

(or sometime may not) be honored when spraying occurs. Usually this

applies to ground-level sprays and not aerial sprays.

 

For more information, see Beyond Pesticides

http://www.beyondpesticides.org/ and Californians for Pesticide

Reform,http://pesticidereform.org/article.php?id=178

 

Sources: PANNA website (www.panna.org); CDC, Human Exposure to

Mosquito-Control Pesticides-Mississippi, North Carolina, and Virginia,

2002-2003 , Morbidity and Mortality Weekly Report (MMWR), June 3,

2005, http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5421a1.htm; CDC; The

National Report on Human Exposure to Environmental Chemicals , July

2005 , http://www.cdc.gov/exposurereport/3rd/; No Spray Nashville,

http://www.nospraynashville.org; AIMM,

http://www.beyondpesticides.org/mosquito/documents/aimm.htm.

Contact: PANNA

 

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