West
Nile Virus - Questions About Spraying And Mosquito Control
How can the risk of West
Nile virus disease be reduced?
The risk of West Nile virus infection and disease can be decreased
by reducing individuals’ exposure to mosquitoes and by taking
special precautions during periods of higher risk of infection including
reducing mosquito populations. A comprehensive mosquito control
program will include several of the following activities:
- Surveillance – regular testing
of mosquitoes and birds for the virus
- Education and Outreach – education
of the public about what steps they can take to prevent mosquitoes
from breeding around their home (e.g., source reduction), and
how to avoid being bitten by mosquitoes (e.g., repair window screens
in your home, wear clothing that covers your skin when outside,
use effective mosquito repellent, etc.)
- Source reduction - elimination of
potential breeding sites by emptying water from containers such
as garbage cans, flower pots, birdbaths, and discarded auto tires
- Larviciding - the application of
chemicals or bacterial products (or larvicides) to mosquito breeding
areas to kill or inhibit the growth of mosquito larvae (the early
stage of the mosquito) from developing into the adult form
- Adulticiding - the application of
pesticide chemicals to kill the adult form of the mosquito. These
are applied by truck-mounted sprayers or aerially in areas where
mosquitoes breed when the risk of an outbreak is apparent as indicated
by increasing numbers of mosquitoes carrying virus and human cases
of disease.
How effective is adulticiding at reducing the number of
adult mosquitoes?
The effectiveness of adulticiding depends on a number of variables
that include: which kinds of mosquitoes are present; what chemicals
are used; when and how often they are applied; current weather conditions;
and the density of homes and streets in a community. It is generally
considered an effective means of temporarily reducing adult mosquito
populations and has been used in the U.S. and other countries for
many years for nuisance reasons and more importantly, as a means
of reducing and preventing mosquito-borne disease. The other activities
listed above – elimination of breeding sites, education and
outreach, and larviciding –precede consideration of adulticide
spraying.
Is all pesticide spraying in Massachusetts in response
to West Nile virus?
No. Spraying to reduce adult mosquito populations has been done
for many years in Massachusetts communities primarily to reduce
nuisance mosquitoes. In addition, there have been occasional years
when the risk of human Eastern Equine Encephalitis (EEE) has been
significant and adulticide spraying has been used to control mosquitoes
to reduce the risk of EEE. EEE is of concern mainly in the southeastern
part of Massachusetts, in Plymouth, Bristol, and some portions of
Norfolk Counties.
What pesticides are used for adulticide spraying in Massachusetts?
Have they ever been used in the Commonwealth before?
Synthetic pyrethroid pesticides are the main pesticides used in
ground spraying operations for adult mosquito control in Massachusetts.
These pesticides (or adulticides) have been used in Massachusetts
for many years. They are chemically similar to pyrethrums, a natural
pesticide produced by chrysanthemum flowers. For ground spraying
operations, resmethrin is usually used. In addition to resmethrin,
adulticide contains another active ingredient called piperonyl butoxide
(PBO), which increases the ability of resmethrin to kill mosquitoes
upon contact and at lower application rates. Other pesticide products
sold in Massachusetts contain pyrethroid ingredients and are generally
used to treat head lice on children and fleas and ticks on pets.
How are the pesticide products typically applied?
Adulticides are typically applied from truck-mounted sprayers as
a fine mist. Most of each droplet is composed of the soybean oil
or mineral oil carrier used to dilute the pesticide product. Mosquitoes
die after they come in contact with the tiny droplets of the pesticide.
Pesticide products that deposit on surfaces as part of a mosquito
control program (e.g., grass, outdoor toys and furniture, etc.)
degrade quickly, particularly once exposed to sunlight. Adulticiding
for West Nile virus is generally performed late at night to target
the particular species of mosquitoes that are known to carry the
virus.
Why do I see mosquitoes on my street the day after adulticide
spraying was done?
There are several reasons why you might see mosquitoes the day
after adulticide spraying. The mist of pesticide cannot reach all
mosquitoes, so you could be seeing ones that were active at the
time of spraying, but did not come in contact with the droplets
of pesticide. Some of the mosquitoes you see may have just emerged
from their breeding sites. Also, different kinds of mosquitoes are
active at different times of the day. Since adulticide spraying
for West Nile virus is usually done late in the evening, those species
of mosquitoes not active at that time would not be affected by the
spraying.
Who decides where to spray adulticides and when? How is
this decision made?
Decisions about whether to spray to reduce WNV risk are made at
the city or town level. Decisions about where and when to spray
are usually made by the local health department or board of health.
Does the State recommend spraying to communities?
MDPH convened meetings of local officials, academic experts, and
other interested people to develop a plan for reducing the risk
of West Nile virus infections. This plan emphasizes prevention and
methods of reducing mosquito numbers that avoid the use of adulticides.
In situations of high risk of an outbreak of human disease, the
MDPH plan recommends consideration of the use of adulticide spraying
to reduce mosquito numbers in those specific areas of high risk.
Who does the spraying of adulticides?
Most pesticide application for mosquito control is done by Regional
Mosquito Control Projects under the management of the State Reclamation
and Mosquito Control Board. The Projects have full-time professional
staff to advise and assist member cities and towns on mosquito control
strategies. Most types of larvicides and adulticides can only be
applied in Massachusetts by the Projects. Cities and towns that
do not belong to a Project and wish to begin mosquito control activities
can either join or contract with a Project or hire commercially
licensed pesticide applicators.
Are pesticide applicators licensed?
Pesticide applicators must be licensed or certified by the Massachusetts
Department of Food and Agriculture Pesticide Bureau. Training for
certification emphasizes integrated pest management and includes
training on the proper use of pesticides, identification of the
specific pest, and knowledge of pest life cycles.
Can some people experience health effects from adulticide
spraying?
Most people are not expected to experience any adverse health effects
after pesticide spraying for adult mosquito control. Some individuals
may be particularly sensitive to ingredients within the product
and experience short-term adverse health effects such as eye, skin,
nose and/or throat irritation, breathing problems, and nausea. You
should call your doctor if you believe that you are experiencing
any symptoms that may be related to pesticide exposure.
What about health effects related to exposure for pregnant
women?
A number of laboratory studies have been conducted that have specifically
addressed the question of whether or not these pesticides are linked
to any developmental or health effects in unborn children. From
these studies, it has been determined that unless a unique and unpredicted
exposure occurred, the spraying of these pesticides for mosquito
control should pose no added risk to pregnant women and unborn children.
Can these targeted ground sprays with adulticides harm
other insects or wildlife?
The US Environmental Protection Agency (EPA) has evaluated these
pesticides for their safety and has determined that they do not
pose an unreasonable risk to birds or mammals if used according
to the product label directions. However, the pyrethroid adulticides
are considered highly toxic to fish and bees. Therefore, these products
are not permitted to be applied to or near open water bodies or
in sensitive environments such as wetlands.
What kinds of precautions should I take when adulticide
spraying is scheduled for my street?
You can reduce your exposure to the insecticide by staying indoors
during spraying. There are otherwise no special precautions that
should be taken. The active ingredients of the pesticide product
generally break down quickly and do not leave a toxic residue.
If individuals want to take extra steps to minimize or
avoid exposure, what steps can be taken?
Common sense steps that can be followed in areas where adulticide
spraying is scheduled to take place include:
- People with asthma and/or other respiratory conditions may
wish to stay indoors, since it is possible that if exposure to
pesticide spray occurred, it could aggravate those conditions.
These individuals may want to consult their physician or local
health department for further advice.
- If the immediate area of your home is being sprayed, keep windows
closed and fans off. Shut off air conditioners unless they have
a setting for recirculating indoor air. If it is very hot weather,
make sure you open the windows and/or turn fans and air conditioners
back on soon after the truck passes your home.
- Rinse any homegrown fruits and vegetables with water as is
typically done before cooking or eating them.
- Keep pets indoors during spraying to minimize their risk of
exposure.
- If skin and/or clothes or other items are exposed to the sprayed
pesticide, wash with soap and water.
- If the spray gets in your eyes, immediately rinse them with
water or eye drops, and call your doctor.
Homeowners can ask to exclude their property from public area-wide
pesticide applications under the Department of Agricultural Resources’
regulation, 333 CMR 13:04, titled Pesticide Board, Exclusions for
Application. To request the exclusion, residents should send a certified
letter to their town or city clerk by March 1st of each year. After
March 1st, Mosquito Control Projects will still try to accommodate
requests. Specific questions regarding the regulation can be answered
by calling the local health department, the city or town clerk,
or the appropriate Regional Mosquito Control Project. The Department
of Agricultural Resources, Pesticide Bureau can also be reached
by calling 617-626-1700.
If you think that you are experiencing any health effects from
pesticides, call your doctor or the Massachusetts Poison Control
Center (800) 222-1222. The MDPH, Bureau of Environmental Health
Assessment may also be consulted by calling (617) 624-5757.
Should I be concerned about covering the swimming pool
in my yard?
All types of pesticides used in spraying operations for adult mosquito
control break down quickly in sunlight and water. Therefore, no
special precautions or waiting periods are recommended for outdoor
swimming pools. However, if a pool is not being used during the
summer months (e.g. if it not being chlorinated or filtered), it
should be covered or drained. Any standing body of water is a potential
breeding ground for mosquitoes.
How do I find out if spraying for mosquitoes will occur
in my neighborhood and when?
Your local health department or board of health will know best
if spraying for mosquitoes is likely to occur in your community.
The MDPH State Laboratory Institute tests mosquitoes for the virus
on a regular basis. A community’s decision to spray may depend
on a number of factors such as the results of mosquito surveillance
efforts, the results of testing of dead birds for the virus, and
the number of dead birds reported to the lab by the public. During
the summer, this information can change from one week to the next,
therefore, it is possible that the decision to spray will be made
only a few days before it will occur. For this reason, check your
local newspaper, radio station, cable television station, the Mosquito
Control Project website at www.state.ma.us/dfa/mosquito/districts.htm,
or your community’s website for updates.
If I work or spend time in other communities where I do
not live, how do I find out if those communities are scheduled for
spraying?
Each community’s health department or board of health or
the office of the Mosquito Control Project to which that community
belongs would have the most accurate information. However, not all
Massachusetts communities belong to a Project. The telephone numbers
for each Project are listed below. Information on the Projects may
also be found on the Massachusetts Department of Agricultural Resources’
website at www.state.ma.us/dfa/mosquito/districts.htm.
Who can I call if I have more questions?
Call your local health department or board of health if you have
any questions about West Nile virus or mosquito control. This fact
sheet and other fact sheets about the virus are available on the
Massachusetts Department of Public Health website (http://www.state.ma.us/dph)
or you can call the MDPH Public Health Information line at 1-866-MASS-WNV
or 1-866-627-7968.
What are some other sources of information on West Nile
virus and pesticides?
You may find additional information at your local library or by
searching the following websites.
For more information about pesticides:
For more information about West Nile virus:
This document was developed in cooperation with the Massachusetts
Department of Public Health, the Harvard School of Public Health,
the Department of Agricultural Resources, and local Boards of Health.
April 2004
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