is West Nile virus?
West Nile virus (WNV) is a mosquito-borne disease. The bite of a mosquito
infected with the virus can cause illness or inflammation of the brain,
known as encephalitis.
Who is at risk?
Anyone that lives in or visits an area with infected mosquitoes is at
risk. People older than 50 years have the highest risk of severe encephalitis.
However, according to CDC, "Less than 1% of those infected with West
Nile virus will develop severe illness
Human illness from West Nile
virus remains rare in areas where it has been reported, and the chance
that any one person is going to become ill from a mosquito bite is low."
Some animals are also at risk, including birds, horses, cats, and domestic
rabbits. Current evidence shows that only mosquitoes can spread the disease,
humans or other animals cannot.
What are the symptoms?
Symptoms of a mild infection include fever, head and body aches, skin
rash, and swollen lymph glands. If you have high fever, experience confusion,
muscle weakness, and severe headaches, call your health care provider
immediately. It may take 3 to 15 days for any of these symptoms to show.
Where is WNV found?
WNV has spread throughout most of the United States. The disease is
also found throughout the world, including Africa, West Asia, Eastern
Europe, and the Middle East.
When is it most
Late summer and early fall is when mosquitoes infected with WN virus
are most common in the United States and other temperate regions such
as Europe. In warmer regions of the world, this disease can occur year-round. top
to Protect from West Nile virus
What can you
- Habitiat Modification - To get rid of mosquitoes, get rid of their breeding sites and exclude
them from your immediate area. Because mosquitoes don't travel far from
where they hatch, you can have a dramatic impact on local mosquito populations
by cleaning up standing water on your property. Get rid of unnecessary
debris on your property; empty water from toys, buckets, birdbaths,
swimming pool covers and any other areas water may be collecting; drill
holes in the bottom of recycling bins and other containers that must
be kept outside; and, clean out rain gutters and make sure that they
are draining properly. Add mosquito-eating fish to ponds or birdbaths
and screen all doors and windows.
- Avoid the Bite - If going outside in the early morning and evening when mosquitoes
are most active, use a hat and wear light-colored long sleeves and pants.
If you choose to use insect repellents, try a natural product especially
when choosing for children. Botanical skin repellents may contain geraniol
(MosquitoGuard or Bite
Stop), citronella (Natrapel),
a combination of soybean and coconut oils (Bite
Blocker), herbal extracts (Beat
It Bug Buster), Avon's
Skin-so-Soft, or other all essential oils (All
Terrain). These are effective mosquito repellents that are safer
than products that contain DEET (N,N-diethyl-meta-toluamide), but should be reapplied often. Several
cases of DEET poisonings have been reported by EPA, including three
fatalities. Always wash off repellents with soap and water once indoors.
Pregnant women should consult a doctor before using essential oils. top
What can your
- Public Education - West Nile virus prevention begins with a strong public education program.
Community officials must educate the public on how to reduce the chance
of mosquito bites through the elimination of breeding habitats and the
proper use of repellents (see above).
- Surveillance - Tracking larval and adult mosquito populations, species types, breeding
locations and virus outbreaks is an essential part of any mosquito management
program. Knowing when and where the virus is likely strike allows for
precise, targeted control techniques.
- Habitat Modification - As on personal property, community land should be cleared of all standing
water that could serve as potential breeding habitat (see above).
- Larviciding - Because not all breeding sites can be eliminated, it is a good idea
to use larvicides, particularly products containing B.t.i. (Bacillus
thuringiensis var. israelensis), in places such as storm drains and
sewer treatment plants. B.t.i. is proven to be effective and is virtually
non-toxic to humans. Methoprene (Altosid) is an endocrine disruptor,
has been linked to wildlife deformities and should not be used. Aside
from traditional larvicides, biological controls, like mosquito-feeding
fish of the Gambia genus, have been used nationwide with great success.
To avoid ecological problems, these fish should only be used in enclosed
bodies of water.
- Protect from
Pesticide Exposure! - If your community insists on spraying, take
all necessary precautions to avoid exposure.
- Leave the area*
- Close the windows
- Turn off air
intake on window unit air conditioners
- Take toys and
lawn furniture inside
- Remove shoes
before entering homes to avoid tracking in residues
- Cover swimming
- Don't let children
play near or behind truck-mounted applicators
Effects of Pesticides Used To Combat Mosquitoes
The Centers of Disease Control and Prevention (CDC) state that spraying
adulticides, pesticides intended to kill adult mosquitoes, is usually
the least efficient mosquito control technique. Aside from adverse health
effects posed to humans, adulticiding is not proven to reduce the risk
of WNV in communities and may actually increase the number of mosquitoes
by destroying their natural predators. Additionally, mosquitoes that survive
the spraying may become resistant and have an increased prevalence of
the virus within their bodies.
Synthetic pyrethroids, which include resmethrin (Scourge) and sumithrin
(Anvil), are adulticides patterned after pyrethrum, an extract from the
chrysanthemum flower. While similar to pyrethrum, synthetic pyrethroids
have been chemically engineered to have greater toxicity and longer breakdown
times . Additionally, almost all synthetic pyrethroid mosquito products
are combined with synergists, which increase potency and compromise the
human body's ability to detoxify the pesticide. Symptoms of exposure include:
dermatitis and asthma-like reactions, nasal stuffiness, headache, nausea,
incoordination, tremors, convulsions, facial flushing and swelling, and
burning and itching sensations . Synthetic pyrethroids are endocrine disruptors
and have been linked to breast cancer . Deaths due to exposure have resulted
from to respiratory failure. People with asthma and pollen allergies should
be especially cautious. Breakdown times range from a few hours in direct
sunlight, to several months in damp, dark environments.
Organophosphates, which include malathion (Fyfanon), naled (Dibrom)
and chlorpyrifos (Mosquitomist), are a highly toxic class of pesticides
that affect the central nervous, cardiovascular and respiratory systems.
Symptoms of exposure include: numbness, tingling sensations, headache,
dizziness, tremors, nausea, abdominal cramps, sweating, incoordination,
blurred vision, difficulty breathing, slow heartbeat, unconsciousness,
incontinence, convulsions and fatality . Some organophosphates have been
linked to birth defects and cancer. Breakdown times range from a few days
in direct sunlight, to several months in damp, dark environments. top
In the United States, WNV is primarily associated with the Culex mosquitoes, also called the "backyard mosquito." Within this
genus, three species, namely C. pipiens, C. restuans, and C. salinarius
make up the majority of those mosquitoes found to be infected with WNV.
Only female mosquitoes take blood meals; males do not bite humans or animals
and usually die one or two days after emerging as adults. In contrast,
adult females may live 2-4 weeks or more, depending on climate, species,
predation, and a host of other factors.
All mosquitoes go
through a four stage life cycle called "complete metamorphosis"
from egg to larva to pupa and finally emerging as an adult. The length
of time that each stage lasts depends on a number of variables with temperature
having the greatest impact.
Eggs are laid in "rafts"
on standing bodies of water. The eggs require one to two days in water
before hatching into first instar larvae.
Larvae, or wigglers, develop as four instars. They molt three times during
ten to twelve days before pupating.
Pupae, or tumblers, metamorphose over one to two days into adults.
Adults emerge from their pupal cases approximately twelve to sixteen days
after being laid as eggs by their mother.
After mating, the
female requires a blood meal in order to produce over 250 eggs. It takes
her three to four days to digest the blood and produce the eggs. Females
transmit diseases when they live long enough to spread infection from
the first blood meal victim to the second blood meal victim. Only a very
small percentage of females live this long. Culex mosquitoes are generally
weak fliers and do not move far from their larval habitat, although they
have been known to fly up to two miles. top
The risks of pesticide exposure to humans and the environment caused
by spraying pesticides are great. Spraying also kills natural predators,
including other insects, birds, and fish. It may also result in mosquito
resistance, which in turn will lead to a larger problem in the future.
Should the community insist on spraying, local decision makers and mosquito
control should be pressed to protect the public and environment from unnecessary
exposure using the following guidelines:
- Identify and
locate the infected mosquito pool(s). As discussed above, an adult
Culex mosquito can fly no further than a two-mile radius. All trapped
mosquitoes should be speciated (to know if mosquitoes are potential
vectors), sexed (only females bite), and tested for the virus (to know
the actual prevelence of the virus). Clear and distinctive thresholds
that determine when a spray may be triggered should be determined with
involvement from the community. Some communities have higher thresholds
for the threat of WNv than others.
- Choose the least
dangerous pesticides. Never use highly toxic pesticides such as
Dursban, Sevin, or Dibrom. Organophosphate pesticides (OPs),
such as malathion and synthetic pyrethroids such as resmethrin and permethrin,
are neurotoxins that can create chronic health effects. Botanical-based
chemicals, including synthetic pyrethroids, are linked to breast cancer
and endocrine disrupters. However, pyrethroids are applied in small
amounts and have shorter residual lives than OPs like malathion.
- Know when to
spray. Mosquitoes take refuge in grass and brush during the day,
so spray at dusk when they are active and most vulnerable. Spray should
never be conducted in winds above 10mph.
- Ensure that
the person spraying is certified. They should use protective clothing
- Alert the
Community 72 hours in advance. Utilize the media and/or
send notices to every household, school, hospital, and business in the
community to tell them when the spraying will occur so they will have
ample time to protect themselves. Alert the public that pesticides are
- Monitor pesticide
equipment calibration and application procedures. Verify that there
is strict compliance with any label instructions, including prohibitions
on spraying and drifting of certain pesticides over bodies of water.
Also, be sure to comply with requirements for storage, disposal, and
equipment cleaning. Mist blower and aerial application of these materials
to populated areas will result in human exposure. We do not recommend
aerial spraying. Rather, spray the pesticides from vehicles or use professional
applicators on foot.
- Provide public
with precautionary measures. Everyone should receive guidelines
on how to reduce exposure to pesticides. Manufacturers and distributors
of pesticides are prohibited by law by ever calling a pesticide safe.
The U.S. Environmental Protection Agency also states that no pesticide
can ever be considered safe. As leaders in the community, never tell
the public that the pesticides are safe, rather, give them information
on how and when to avoid exposure.
- Advise hospitals
and schools. Also notify other buildings with especially vulnerable
populations to take extra precautionary measures to prevent pesticides
from entering buildings.
- Monitor public
and environment for adverse effects from the spraying. If WNv is
a problem, the last thing to do is create another problem by not monitoring
potentially adverse effects. Set up a hotline for receiving reports,
collecting hospital records, and requiring physician reporting of incidents.
Use wipe tests of outdoor and indoor surfaces, check air conditioner
filters, evaluate water samples, and conduct soil and food residue tests
from gardens and farms.top
* Infants, children,
pregnant women, the elderly, and individuals with compromised immune systems
and chemical sensitivities are especially vulnerable and must take extra
care to avoid pesticide exposure.
For a more detailed
report by Beyond Pesticides see Public Health
Mosquito Management Strategy- For Decision Makers and Communities (Revised August 2004). If you are concerned about improper mosquito management
in your community, learn what you can do by visiting Tools