Protection Strategies Against West Nile Virus
Preventing West Nile Virus (WNV)
The basis of preventing WNV in Scouts, Scouters, and camp staff is a
two-pronged program directed at mosquito reduction and personal protection.
By far the most important aspect is personal protection. The Department of
Defense system of personal protection consists of treating clothing with
0.5% permethrin and treating exposed body surface areas with DEET. Properly
used, this combination can reduce the incidence of mosquito bites by
virtually 100 percent. 
West Nile Virus (WNV) was first identified in a patient in Uganda in
1937. In August 1999, two cases of this disease were found in patients
in Queens, New York. WNV spread to 44 states and the District of Columbia
by the end of 2002, with thousands of cases of severe disease and more
than 200 deaths.
For every five humans infected with the virus, one has a mild, febrile
illness lasting 3 to 6 days, while approximately one in 150 infected
persons develops meningitis or encephalitis. The incubation period ranges
from 2 to 14 days. Mild illness may include lethargy, eye pain, nausea,
cramping and a rash. Severe muscle weakness is also frequently a
WNV develops in humans from infected mosquito bites. Birds act as an
intermediate host, forming a reservoir of infection. Migrating birds
introduce the WNV into local ecosystems where it may then continue to
reside in wintering species of mosquitoes in some areas of the country,
or be reintroduced to new hatches of mosquitoes in the spring.
Maps indicating the current spread of WNV can be found at the U.S.
Geological Survey internet site:
Article I. Mosquito Reduction Methods
The term source reduction refers to altering habitats that temporarily
hold water. Community mosquito control agencies do so by clearing culverts,
storm water collection structures, roadside ditches, etc., and by altering
water flows in salt marshes. It is important to prevent buckets, tires,
and other such items from collecting water. Birdbaths should be rinsed
weekly because mosquito larvae (the aquatic stage) require only 1 week to
develop to adults. One tire can produce thousands of mosquitoes in one
summer. Because mosquitoes tend not to fly far, those produced on camp
property will remain a nuisance to the immediate area.
The camp property abatement plan should include the following:
- Repair failed septic systems.
- Keep grass cut short and shrubbery trimmed.
- Dispose of old tires, cans, plastic containers, ceramic pots,
or other unused containers that can hold water
- For those containers that must remain on your property, such
as bird baths and wading pools, change the water at least
once a week.
- Cover trash containers to keep out rainwater
- Clean clogged roof gutters, particularly if leaves tend to
clog the drains
- Repair leaky water pipes and outside faucets.
- Aerate ornamental pools or stock them with predatory fish
- Clean and chlorinate swimming pools even if they are not
- Keep drains, ditches, and culverts free of grass clippings,
weeds, and trash so water will drain properly.
Larviciding refers to killing larvae before they become adults.
Community control programs do so by applying environmentally benign
products to habitats that, for various reasons, cannot be drained.
While homeowners can purchase BTI - an environmentally benign,
slow-release briquette product, source reduction is usually the more
appropriate tactic on camp property.
Adulticiding refers to killing adult mosquitoes. Community
control programs do so by spraying from trucks or backpack foggers.
This is the method of last resort because adults are dispersed and no
environmentally benign products are available to kill adult mosquitoes.
All adulticides will kill other beneficial insects that receive
sufficient dosages. Also, ground-based spraying has limited
effectiveness in both space and time. However, various equine
encephalitis outbreaks and WNV emergencies can warrant ground and/or
aerial spraying to quickly reduce a human health threat.
Individual state incidence information on WNV and points of contact
with local health authorities for specific advice on local risk of
disease and help with issues of mosquito abatement procedures can be f
ound for each state at:
Personal Protection Technique
Clothing protection with permethrin is safe and effective for up to 6
weeks. Spraying 0.5% permethrin on the cloth until the material is damp
treats the clothing adequately. Spray outdoors and allow to dry before
wearing. This water-based substance is safe for all fabrics, natural and
synthetic. The chemical does not absorb through skin and is non-irritating.
The impregnated fabric can withstand multiple washings or wetting (such as
rain or immersion while swimming) over a 6-week period before requiring
re-application. A video demonstration of how to apply permethrin to
clothing prepared for consumers can be found at:
Permethrin has a high safety factor because it breaks down when exposed
to human skin due to an enzyme action. This rapid metabolic degradation,
together with incomplete absorption, contributes to the low acute toxicity
of the synthetic pyrethroids. This generic product can be found in
camping specialty stores and major drug store and retail stores throughout
the United States.
An insect repellent containing DEET should be used on exposed skin
surfaces when mosquitoes are present. Low absorption formulations of DEET
are available. It is preferable to use a DEET concentration of not more
than 35%. DEET is the most effective and best studied insect repellent on
the market with a remarkable safety profile after 40 years of worldwide
When applying DEET, care must be taken to avoid allowing the repellent
to contact the eyes or mouth. DEET can also dissolve some synthetic
materials. If sun block is also necessary, apply the DEET lotion after
applying sun block. Weak solutions of DEET (less than 10 percent) will
have to be frequently re-applied where there are heavy mosquito
concentrations. Under these conditions the higher concentrations offer
superior protection. Controlled release and composite formulations of
DEET can be very effective in concentrations of 12 to 20 percent (3M
Ultrathion, Sawyer Controlled Release), but otherwise, 30 to 35 percent
DEET concentrations are the most appropriate for use in high-density
A consumer site that discusses DEET application strategies for
youngsters and children can be found at:
A 111 page document prepared by the Centers for Disease Control
that discusses WNV prevention strategies can be downloaded in Adobe
Acrobat format from:
||Fradin, MS. Mosquitoes and mosquito repellents: a clinician's
guide. Ann Intern Med (1998 Jun1) 128 (11):931-40.|
||Miyamoto, J. Degradation, metabolism and toxicity of synthetic
pyrethroids. Environ Health Perspect (1976) 14:14-28|