with West Nile Virus in the U.S.
In August 2003, West Nile Virus (WNV) was detected in birds along an
important bird migration route in southeastern California. In the four
years since the virus was first found in North America, its westward march
across the continent has stirred public health officials and communities to
adopt different protective strategies, from massive spray programs to
community education and improved surveillance, to "no spray"
resolutions. However, information on the effectiveness of many mosquito
abatement strategies is still unavailable. For example, the efficacy of the
widespread spraying for adult mosquitoes is still unknown, and may actually
increase mosquito populations. Also unknown are the impacts of this
spraying on public health and wildlife.
The first U.S. human case of WNV was reported in 1999 in New York State.
Since then the number of human cases has increased each year, in late
November 2003 the U.S. Centers for Disease Control (CDC) reported 8,567
human cases and 199 deaths in 2003, up from 4,156 cases and 214 deaths in
2002. Most people who contract WNV do not experience symptoms. According to
the CDC, about 13% of those infected develop symptoms and one in 150 people
develop meningitis, an infection of the spinal cord, or encephalitis, an infection
of the brain.
In the years since the first outbreak, the CDC and local vector control
agencies have altered their public recommendations for dealing with West
Nile. There is now greater emphasis on public education, the removal of
standing water as mosquito breeding sites, and selective application of larvicides instead of widespread use of sprays
targeting adult mosquitoes (adulticides).
Aerial spraying of insecticides continues in many places however, even
though it may increase mosquito populations by decimating the predators. A
recent report from Pesticide Watch, warning that pesticide spraying for WNV
in California may do more harm than good, notes that two organophosphate
pesticides, malathion and naled,
are approved for use in California against mosquitoes. Organophosphate
pesticides are cholinesterase inhibitors, affecting the nervous system.
Exposures can cause nausea, dizziness, and confusion. Residents in New York
City complained of allergic reactions and flu-like symptoms when malathion was sprayed for WNV. Naled
(sold as Dibrom) has been associated with stomach
cancers, pancreatic tumors and leukemia in laboratory animals. Trichlorfon, an ingredient in naled
has also been associated with in utero
neurological damage in test animals.
Synthetic pyrethroids, such as sumithrin (Anvil) and permethrin
are also widely used against mosquitoes in the U.S. Both can cause
dermatitis and asthma-like reactions. When sumithrin
was sprayed for West Nile carrying mosquitoes in New York in 2000, the health
department reported 200 calls to the city's hotline for pesticide
poisoning. Permethrin is a possible human
carcinogen, and studies have shown it mimics the hormone estrogen, which
can cause breast cancer, lower sperm counts, and affect sexual traits as
well as childhood development.
The efficacy of insecticide sprays within cities and towns is another
unknown. Unlike agricultural fields, where obstacles are few and vegetation
is relatively uniform, a chemical mist on a city street is subject to
buildings and other barriers and is unlikely to affect insects in backyards
or protected by shrubbery. Even more problematic are the timeframes for
spraying. West Nile carrying mosquitoes are most active, and spraying is
most effective, at dawn or dusk, both times when people are going to or
coming from work. Several cities and towns have vowed not to spray adulticides for West Nile. Lyndhurst, Ohio, a suburb of
Cleveland, passed a landmark ordinance in early July 2003, and Ft. Worth,
Texas and Washington, DC have both pledged not to spray.
The health risks of mosquito repellent -- particularly for infants and
children -- are also not well understood. The Centers for Disease Control
website warns those outside at dawn or dusk to apply a mosquito repellent
containing DEET, (N,N-diethyl-m-toluamide) and reapply as needed. Yet DEET is a
neurotoxin, and can impact brain development. Therefore a fetus, infant or
small child is especially vulnerable. In many countries in Europe
and Africa DEET is not registered for use, due to health concerns.
A recent report by Marion Moses of the Pesticide
summarizes what is known about health effects of DEET on children and
adults. Dr. Moses says, "We know that DEET affects the brain because
it causes seizures. DEET labeling advice should strongly caution against
any use by pregnant women or children under the age two and should list
symptoms of neurotoxicity." PANNA's online diagnostic tool for symptoms of
pesticide poisoning (see story on page 12) indicates symptoms of acute
exposure to DEET may include headaches, restlessness, irritability, eye and
mucous membrane irritation, crying spells and other changes in behavior.
More severe symptoms include slurred speech, tremors, seizures and coma.
In its short time in North America, WNV has
brought a new urgency to mosquito control, and has galvanized some
communities to develop more health protective control strategies. As a
virus that carries the greatest risk to the very old, young or those with
suppressed immune systems, it has elicited recommendations for DEET that
may place even greater risk on those most vulnerable. What WNV has not
brought may be the most needed of all -- a full evaluation of the human
health and environmental effects, and the efficacy of widespread pesticide
spraying to control adult mosquitoes. And, while they're at it, a new
assessment of the risks of DEET.
Resources: The website for Beyond Pesticides/National Coalition
Against the Misuse of Pesticides has information on WNV and how to work
with your community to adopt a safer mosquito control strategy. http://www.cdc.gov/ncidod/dvbid/westnile/index.htm.
Sources: Why Pesticide Spraying for West Nile Virus in
California May Cause More Harm than Good, Pesticide Watch, August 2003;
Summary of Adverse Health Effects of Deet in
Children and Adults, Marion Moses M.D., Pesticide Education Center,
September 20, 2003; Centers for Disease Control website http://www.cdc.gov/ncidod/dvbid/westnile/index.htm.