Eight Reasons Why
Spraying Pesticides
is Not the Solution to
West Nile Virus
by Rebecca Watson
UPdate Spring 2003
How much of a risk is West Nile Virus
(WNV)? To some extent, only time will tell. But public health experts stress
that there is no cause for fear and panic, or for panic driven "solutions."
In fact, the so-called "solution" of spraying pesticides to kill mosquitoes
will actually lead to bigger problems. Here are eight compelling reasons
why spraying pesticides is not the answer to WNV.
1. Least Effective Measure
The US Center for Disease Control and
other experts say that spraying or fogging is the least effective means
for slowing the spread of WNV carrying mosquitoes. For fogging to
have maximum effect, a mosquito has to be flying. Estimates are that fogging
kills only about 10% of adult mosquitoes. The federal-provincial
task force on WNV admits there is little evidence for the efficacy of insecticide
spraying. Adult mosquitoes live only about two weeks, with new larvae
hatching constantly. This means that spraying cannot be a one shot operation,
but needs to be repeated
frequently if chosen as a means of
control .
2. Predators Harmed,
Mosquitoes Thrive
Aerial spraying or fogging is more
harmful to mosquito predators than to mosquitoes. Since predators are farther
up the food chain, they will take in higher amounts of pesticide. By decreasing
mosquito predator populations, aerial spraying actually leads to increases
in mosquito populations. Data from a study in New York State published
in the Journal for Mosquito Control found that after 11 years of
insecticide spraying, the mosquito population had increased 15 times. Pesticide
exposure also results in immune suppression in birds, which serve as the
hosts for WNV. Birds exposed to organophosphate pesticides
tend to suffer immune suppression (as do mammals, amphibians and other
animals.) This makes them less able to fight off viral and bacterial infections,
the very opposite of what is needed. Once infected with WNV, birds are
more likely to develop symptoms and to remain ill longer than if they had
not been exposed. Thus, pesticide spraying leads to more frequent and longer
infections and higher viral loads in birds, making it more likely they
will spread the disease to mosquitoes. This increases the possibility
of
mosquitoes transmitting the virus to
humans and other mammals.
3. Super Mosquitoes, Sicker
Mosquitoes
For some reason, as yet unknown, mosquitoes
exposed to pesticides are more
likely to have WNV in their salivary
glands and develop a damaged gut lining which becomes more porous, allowing
WNV to pass through. Over a decade of insecticide spraying to control encephalitis
in Florida has not been effective, and mosquitoes are now 15 times more
likely to pass on the disease. Mosquitoes, which have short life spans,
go through many generations in a single year. The mosquitoes which
are exposed to pesticides and survive are more likely to develop resistance
to them. So
aerial spraying contributes to the
development of "super mosquitoes" which can only be killed by using higher
amounts or different types of pesticides.
4. Immediate Human Health
Effects
Immediate health effects on humans
from exposure to sprayed pesticides are
considerable. A letter from 26 prominent
physicians and scientists in Quebec released last summer states, "Indiscriminate
spraying of pesticides, especially in heavily populated urban areas, is
far more dangerous to human health and the natural environment than a relatively
small risk of West Nile Virus.... Ironically, such spraying is especially
dangerous to those with impaired immunity for whose 'protection' such spraying
is mainly being done. ..Those individuals who are most vulnerable in this
chemical action against mosquitoes include children, pregnant women, the
elderly, chemically sensitive and immuno-suppressed individuals, such as
patients with AIDS and cancer, and people suffering with asthma and other
allergies." Organophosphates
are the most common class of pesticides used in mosquito control sprays.
According to the United States Environmental Protection Agency (EPA), they
are "efficiently absorbed by inhalation, ingestion and skin penetration"
and were "the class of pesticides most often implicated in symptomatic
illnesses among people in 1996."
5. Long Term Health Effects
Pesticides used in mosquito control
can contribute to immune suppression in humans. A report from the World
Resources Institute notes, "Impairment of the immune system by chemical
pesticides can lead to allergies, auto immune disorders such as lupus,
and cancer. It may also lead to infections to which one may be normally
resistant." People with weakened immune systems are the most vulnerable
to WNV. Thus, in the long term, aerial spraying may actually increase the
number of people who become seriously ill from WNV. And immune system
suppression has serious implications for other diseases as well, including
SARS.
Malathion, Naled and Resmethrin are
pesticides commonly used in mosquito control. Malathion, an organophosphate,
is neurotoxic. It is the most common pesticide used in aerial spraying.
In studies on rats, pesticides were shown to impair the blood-brain barrier.
In humans, the more serious effects of WNV occur when the virus crosses
the blood-brain barrier. Malathion, like all members of the organophosphate
family, disrupts nervous system function. Besides causing headaches,
nausea and diarrhea, it has been linked to gene damage causing attention
deficit hyperactive disorder (ADHD). Other heath hazards identified in
laboratory studies include damaged sperm, altered immune function, increased
incidence of breast tumors, and increased risk of non-Hodgkin's lymphoma.
Naled is another organophosphate which disrupts nervous system function,
also causing headaches, nausea and diarrhea. Naled is most toxic when exposure
occurs by inhalation. Lab tests connected exposure to Naled's breakdown
product, dichlorvos, to aggressiveness and deterioration of memory and
learning. Dichlorvos is also classified as a carcinogen, and interferes
with prenatal brain development.
Resmethrin is considered by the World
Health Organization as a "neuropoison." Its effects on the human nervous
system are similar to its effects in insects. Lab studies on rats showed
that Resmethrin interfered with reproduction, increasing numbers of stillborns
even at the lowest exposure tested.
6. Long Term Environmental
Effects
Most of the pesticides presently used
for mosquito control do not selectively target mosquitoes. Malathion, Naled
and Resmethrin kill all insects. This includes hundreds of beneficial insect
species that pollinate crops and keep pests under control. Malathion
is known to contaminate water, and is classified as highly toxic to most
species of fish. In 1999, 90% of adult lobsters in Long Island Sound were
killed by malathion used on land. Fish kills in the thousands have been
reported following mosquito spraying. Since some species of fish feed on
mosquito larvae, this is
doubly counterproductive. Other organisms
that feed on mosquito larva are also killed. Bird populations are also
threatened. According to New York State wildlife
pathologist Ward Stone, more
of the birds sent to his unit for examination in 2000 died from pesticides
than from WNV. Among the more frequent causes of bird death were broad
band insecticides from the organophosphate category such as Dursban, diazinon
and ethylparathion. Organophosphates used in mosquito control add harmful
volatile organic compounds (VOCs) to the atmosphere, and are precursors
of ozone (smog) forming chemicals. This means they are contributors to
global warming.
7. Keep Risk in Perspective
While the image of a new killer virus
from the tropics is scary and makes for good media material, public health
experts at all levels are attempting to help people put WNV in perspective.
West Nile Virus is less dangerous than the flu. Only 1% of mosquitoes carry
the WNV, even in places where WNV has been common for years. Because of
our climate, the virus is not expected to overwinter, but would likely
be reintroduced each year through bird migration. Less than 1% of people
bitten by infected mosquitoes will have any symptoms, and most of those
will be equivalent to a one day flu or headache. Studies in New York when
WNV was most widespread found thousands of people who tested positive for
WNV but had never experienced any symptoms of illness. People bitten by
infected mosquitoes, even those who
experience no symptoms, will develop
a lifetime immunity to the disease. In Africa and Europe, the virus occurs
in cycles, with typically three years of human infections in late summer,
with the majority of infections in the first year of a cycle. Then the
virus fades into the background, and may not reappear for many years.
In Africa, WNV is a childhood disease; adults have developed immunity.
8. Taking a Long-term
Approach
WNV may be one of a number of tropical
diseases which will spread to our geo- graphic area with global warning.
Instead of panic and sensationalism, we need a rational, long term problem-solving
approach which is healthy for humans and the environment. Reducing
mosquito breeding sites (standing water), known as source control, is the
most effective mosquito control method. Since adult mosquitoes
seldom travel more than 1 kilometer,
source control in a neighborhood can be extremely effective and quite non-toxic.
Experts stress the value of source controls such as mechanical flushing
of sewer catch basins, and introduction of dragonfly larvae in nearby ponds
and lakes. These methods have been practiced with great success in Wells,
Maine for 26 years. Maintaining healthy mosquito predator populations
is an important part of a mosquito control strategy. Eliminating
mosquito larvae, through predators and biological means and if absolutely
necessary via pesticides, is far more effective than trying to kill adult
mosquitoes. And ultiimately, the most effective defense against WNV is
a healthy ecosystem and a healthy immune system in humans, birds and other
species.
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Rebecca Watson
is a writer with a special interest in environmental health.
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