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#709 - West Nile Virus -- Part 1, 11-Oct-2000

by Rachel Massey*

West Nile virus (WNV), a disease previously unknown in the
Western Hemisphere, appeared in New York City last year and has
now spread to animal populations in six other states. Some
municipal officials have responded to the disease by spraying
entire neighborhoods with pesticides intended to kill
mosquitoes. West Nile Virus can cause serious illness and death
in some cases, but spraying pesticides to kill mosquitoes is not
a good solution. Spraying exposes large numbers of people to
toxins with both short- and long-term health effects, and
studies suggest it is unlikely to be effective.

Transmitted by mosquitoes, WNV primarily attacks birds but can
also infect humans and other animals. Most infections with WNV
go unnoticed or feel like an ordinary flu, but some cases lead
to encephalitis (inflammation of the brain) or meningitis
(inflammation of the membranes surrounding the brain and spinal
cord) and can be fatal. The elderly and individuals with
compromised immune systems may be particularly vulnerable to
serious illness resulting from the virus.

In 2000, WNV has reappeared in New York City, and infected birds
have been found in upstate New York as well as New Jersey,
Massachusetts, Rhode Island, New Hampshire, Connecticut, and
Maryland.[1] In the 1999 outbreak, sixty-two people became
seriously ill and seven died. The individuals who died of the
virus ranged from 68 to 87 years of age.[2] Of the fifty-five
individuals in New York City who survived severe cases of the
virus, some continue to suffer neurological problems a year

As of October 7, a total of 17 human cases of WNV had been
detected this year, 3 in New Jersey and 14 in New York.[4] One
individual, an 82-year-old man in New Jersey, has died of the
virus this year.[5] Recent outbreaks have occurred in other
countries as well; in Israel, over 120 people have shown
symptoms of WNV infection this year and 10 have died.[6]

In a study conducted last summer, researchers tested blood from
677 randomly selected individuals in a 4-square-mile area around
the focal point of the outbreak in Queens, N.Y. Of these 677, 19
showed evidence of having been infected with West Nile virus.
Based on these results, the researchers estimated that 2.6% of
the individuals in the area studied were infected with the
virus. About a fifth of these exposed individuals had
experienced symptoms attributable to the virus. This study
supports the view that most individuals infected with the virus
never develop noticeable symptoms.[7] The Centers for Disease
Control (CDC) estimates that the case-mortality rate for WNV
(the proportion of individuals showing symptoms who die of the
disease) is three to fifteen percent, with the fifteen percent
figure applying to the elderly.[8]

Mosquitoes begin life as eggs laid in stagnant water; later they
change into water-dwelling larvae, then pupae, and finally
adults. Thus they can be controlled by several means -- by
minimizing standing water, by maintaining populations of egg- or
larva-eating fish, or by applying chemicals that kill either
larvae or adults.

New York City responded to the appearance of the virus last year
by spraying the organophosphate insecticide malathion from
trucks and helicopters to kill adult mosquitoes.
Organophosphates act as nerve toxins, disrupting the nervous
system by inhibiting the enzyme cholinesterase. Short-term
symptoms resulting from human exposure to organophosphates can
include breathing problems, headache, nausea and dizziness. High
exposures can produce fatal poisoning.[9] In April 2000, a U.S.
Environmental Protection Agency (EPA) committee reviewed a
series of studies on mice and rats exposed to malathion. Based
on this review, the committee concluded that there was
"suggestive evidence of carcinogenicity" which was "not
sufficient to assess human carcinogenic potential."[10] For the
moment malathion remains listed by EPA as "not classifiable"
with regard to carcinogenicity. Malathion is also a suspected
hormone disrupter.[11]

This year, New York and other municipalities have used
pyrethroid insecticides such as Scourge (active ingredient,
resmethrin) and Anvil (active ingredient, sumithrin) to kill
adult mosquitoes. The pyrethroids also act as nerve toxins, and
may have other long-term health effects. Resmethrin has been
found to act as a weak hormone mimic in test tube studies.[12] A
1999 study on how pyrethroids affected breast cancer cells in a
laboratory setting led researchers to suggest that the
pyrethroids as a group should be considered hormone
disrupters.[13] EPA is scheduled to re-evaluate the health
effects of the pyrethroids in 2002.

Pyrethroids are also very toxic to fish and to bees, and there
are regulations against applying them on or near bodies of
water.[14] It is particularly important to pay attention to
their effects on fish when designing a mosquito control program,
since healthy fish populations can serve as an important natural
mosquito control.

Like several other pyrethroid insecticides, Scourge and Anvil
contain piperonyl butoxide (PBO), which is added to enhance the
toxicity of the active ingredients. Studies have linked PBO
exposure to liver cancers in rats and mice,[15] and it is
classified by the EPA as a possible human carcinogen. There is
also some evidence that PBO-pyrethroid mixes can affect the
human immune system.[16]

Intentionally spraying thousands of people with suspected
carcinogens or hormone disrupters seems dubious from a public
health perspective. Potential effects on fetuses, infants, and
children are of particular concern. Increasing evidence supports
the view that even tiny exposures to toxic chemicals can have
devastating effects on infants and developing fetuses, depending
when the exposures occur.[17]

There has been considerable variation in responses to WNV this
year. When infected birds began appearing in the Boston area,
several municipalities began aggressive spraying to kill adult
mosquitoes in an area defined by a two-mile radius around the
site where an infected bird was found. Buffalo, N.Y., on the
other hand, has limited itself to the use of larvicides placed
in standing water without spraying.[18]

Some municipalities have used chemical larvicides such as
Altosid (active ingredient, methoprene), to kill mosquito larvae
in catch basins and other standing water. When exposed to
sunlight, methoprene breaks down into a class of chemicals
closely related to vitamin A, known as retinoids, which can
cause birth defects in humans and may be contributing to the
global epidemic of skeletal deformities in frogs (see REHW #590
and #623 ). Other municipalities have opted for least-toxic
control measures, including the use of BACILLUS THURINGIENSIS
bacteria that are toxic to mosquito larvae.

Long-term health effects of spraying pesticides in urban areas
are probably the greatest concern, but acute exposures can also
be a problem. Municipal officials in charge of spray programs in
New York and other cities warned residents to remain indoors
during the scheduled spray times, closing windows and turning
off air conditioners to prevent the chemicals from entering
their homes. But in one case, a New York resident was sprayed at
close range when trucks began spraying at 10:00 pm rather than
at midnight, as they had been scheduled to do.[19] At an April,
2000 meeting in New York, several people said they thought they
were suffering neurological problems resulting from the
spraying, and one doctor said she had seen 160 patients with
minor neurological problems possibly attributable to the

[To be continued.]


* Rachel Massey is a consultant to Environmental Research

[1] "Update: West Nile Virus Activity --- Northeastern United
September 15, 2000, pgs. 820-2. And: "West Nile virus continues
to spread south in US," Reuters Health Information, September
22, 2000. See www.reutershealth.com.

[2] New York City Department of Health, "West Nile Virus: A
Briefing," CITY HEALTH INFORMATION Vol. 19, No. 1, May 2000, pg.

[3] David W. Chen, "Lives that have been changed forever from
the aftereffects of a mosquito bite," NEW YORK TIMES August 19,
2000, pg. B1

[4] United States Department of Agriculture Animal and Plant
Health Inspection Service (APHIS), "Update on Current Status of
West Nile Virus, Week of 1 October through 7 October, 2000."
Available at http:www.aphis.usda.gov/oa/wnv/wnvstats.html.

[5] Grant McCool, "N.Y. reports its 14th case of West Nile
virus," Reuters Health Information, October 5, 2000. See

[6] "West Nile virus continues to spread south in US," Reuters
Health Information September 22, 2000. See

[7] New York City Department of Health, "West Nile Virus: A
Briefing," CITY HEALTH INFORMATION Vol. 19, No. 1, May 2000, pg.

[8] Centers for Disease Control, "West Nile Virus: Questions and
Answers." Available at http:www.cdc.gov/ncidod/dvbid/westnile/-q&a.htm
(omit the hyphen).

[9] J. Routt Reigart and James R. Roberts, RECOGNITION AND
Environmental Protection Agency Office of Pesticide Programs,
1999). Available at http:www.epa.gov/oppfead1/safety/healthcare/-
handbook/handbook.htm (omit the hyphen). For a thorough overview
of malathion's health effects see Loretta Brenner, "Malathion,"
JOURNAL OF PESTICIDE REFORM Vol. 12, No. 4, Winter 1992, pgs.

[10] Cancer Assessment Review Committee, Health Effects
Division, Office of Pesticide Programs, "Cancer Assessment
Document #2: Report of the 12-April-2000 Meeting: Evaluation of
the Carcinogenic Potential of Malathion." Available at http:-
www.epa.gov/pesticides/op/malathion.htm (omit the hyphen).

[11] Stephen Orme and Susan Kegley, PAN Pesticide Database. San
Francisco: Pesticide Action Network, 2000.

[12] Ted Schettler and others, GENERATIONS AT RISK: REPRODUCTIVE
HEALTH AND THE ENVIRONMENT. (Cambridge, Mass.: MIT Press, 1999),
pg. 186.

[13] Vera Go and others, "Estrogenic Potential of Certain
Pyrethroid Compounds in the MCF-7 Human Breast Carcinoma Cell
1999, pgs. 173-177.

[14] U.S. Environmental Protection Agency, "For Your
Information: Synthetic Pyrethroids for Mosquito Control,"
(Washington, D.C.: U.S. Environmental Protection Agency, May
2000). Publication #735-F-00-004.

[15] O. Takahashi and others, "Chronic Toxicity Studies of
Piperonyl Butoxide in F344 Rats: Induction of Hepatocellular
February 1994, pgs. 293-303. And: O.Takahashi and others,
"Piperonyl butoxide induces hepatocellular carcinoma in male
CD-1 mice." ARCHIVES OF TOXICOLOGY Vol. 68, No. 7, July 1994,
pgs. 467-9.

[16] F. Diel and others, "Pyrethroids and piperonyl butoxide
affect human T-lymphocytes in vitro." TOXICOLOGY LETTERS , Vol.
107, Nos. 1-3, June 1999, pgs. 65-74.

[17] See Schettler, cited above in note 12, pgs. 12-16, or John
Wargo, OUR CHILDREN'S TOXIC LEGACY (New Haven: Yale University
Press, 1998), pgs. 173-8.

[18] Megan Scott and Beth Daley, "Spraying for West Nile
Begins," BOSTON GLOBE July 28, 2000, pg. A1. And: Raja Mishra,
"Researchers Mark West Nile Hot Spots," BOSTON GLOBE August 11,
2000, pg. B2. And: Kevin Collinson and Henry L. Davis, "More
Funds Allocated to Fight West Nile Virus," BUFFALO NEWS
September 1, 2000, [Local, pg. 1C].

[19] Elisabeth Bumiller, "Mayor Says Pesticide Spraying Victim
Was Right," NEW YORK TIMES September 12, 2000, pg. B5.

[20] "Officials Defend Spraying to Curb West Nile Virus," NEW
YORK TIMES April 1, 2000, pg. B3.

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