Relevant information regarding questions on mosquito control
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In early June, I sent two articles to AFRO-NETS regarding mos-
quito control. Following is another to add to the collection on
what and how things are being done in the U.S. about West Nile
Virus. While the vector may be a different species from those
delivering malaria in Africa, it is great to hear someone (Peter
Burgess) speak out about the inadequacies of the approaches
taken to date�use on �bednets� as the primary means of limiting
the incidence of malaria in Sub-Saharan Africa � effective as
that is in limiting the incidence when used correctly and con-
sistently.
However, to balance the picture out, no amount or frequency of
spraying will reduce the mosquito population to zero. Therefore,
without the concomitant use of medication, to reduce the preva-
lence of the disease, it will be difficult to show significant
cost effectiveness of spraying in an already highly infected
population. I believe evidence and logic support that fundamen-
tal notion that only a comprehensive approach is the only means
of tackling the malaria problem. I trust that those who are
dealing with this massive problem on a daily basis find both the
logic appropriately applied and the article useful.
Joint Statement on Mosquito Control in the United States from
the U.S. Environmental Protection Agency (EPA) and the U.S. Cen-
ters for Disease Control and Prevention (CDC).
1. The Role of Government Agencies and the Public
http://www.epa.gov/pesticides/factsheets/mosquitojoint.htm#role
2. Diseases Transmitted by Mosquitoes
http://www.epa.gov/pesticides/factsheets/mosquitojoint.htm#disease
3. Mosquito Life Cycle
http://www.epa.gov/pesticides/factsheets/mosquitojoint.htm#cycle
4. Mosquito Control Programs
http://www.epa.gov/pesticides/factsheets/mosquitojoint.htm#programs
5. Integrated Pest Management
http://www.epa.gov/pesticides/factsheets/mosquitojoint.htm#ipm
6. Education
http://www.epa.gov/pesticides/factsheets/mosquitojoint.htm#education
7. For More Information
http://www.epa.gov/pesticides/factsheets/mosquitojoint.htm#info
Mosquito-borne diseases are among the world's leading causes of
illness and death today. The World Health Organization estimates
that more than 300 million clinical cases each year are attrib-
utable to mosquito-borne illnesses. Despite great strides over
the last 50 years, mosquito-borne illnesses continue to pose
significant risks to parts of the population in the United
States. Current challenges posed by the emergence of West Nile
virus in the Western hemisphere illustrate the importance of co-
operation and partnership at all levels of government to protect
public health. The Environmental Protection Agency (EPA, the
Agency) and the Centers for Disease Control and Prevention (CDC)
are working closely with each other and with other federal,
state, and local agencies to protect the public from mosquito-
borne diseases such as the West Nile virus.
1. The Role of Government Agencies and the Public
CDC, working closely with state and local health departments,
monitors the potential sources and outbreaks of mosquito-borne
diseases and provides advice and consultation on prevention and
control of these diseases. CDC works with a network of experts
in human and veterinary medicine, entomology, epidemiology, zo-
ology, and ecology to obtain quick and accurate information on
emerging trends which they develop into national strategies that
reduce the risk of disease transmission.
EPA ensures that state and local mosquito control departments
have access to effective mosquito control tools that they can
use without posing unreasonable risk to human health and the en-
vironment. EPA encourages non-chemical mosquito prevention ef-
forts, such as eliminating standing water that provide breeding
sites. The Agency educates the public through outreach efforts
to encourage proper use of insect repellents and mosquitocides.
Additionally, EPA's rigorous pesticide review process is de-
signed to ensure that registered mosquitocides used according to
label directions and precautions can further reduce disease-
carrying mosquito populations.
State and local government agencies play a critical role in pro-
tecting public health from mosquito-borne diseases. They serve
on the front line, providing information through their outreach
programs to the medical and environmental surveillance networks
that first identify possible outbreaks. They also manage the
mosquito control programs that carry out prevention, public edu-
cation and vector population management.
The public's role in eliminating potential breeding habitats for
mosquitoes -- such as getting rid of any standing water around
the home -- is a critical step in reducing the risk of mosquito-
borne disease transmission. The public is also encouraged to
make sure window screens and screen doors are in good repair.
When venturing into areas with high mosquito populations, the
public should wear personal protection such as long sleeve
shirts and long pants, preferably treated with a repellent..
People should use mosquito repellents when necessary, and always
follow label instructions.
2. Diseases Transmitted by Mosquitoes
Mosquitoes are found throughout the world and many transmit
pathogens which may cause disease. These diseases include mos-
quito-borne viral encephalitis, dengue, yellow fever, malaria,
and filariasis. Most of these diseases have been prominent as
endemic or epidemic diseases in the United States in the past,
but today, only the insect-borne (arboviral) encephalitides oc-
cur annually and dengue occurs periodically in this country. The
major types of viral encephalitis in the United States include
St. Louis, LaCrosse, Eastern equine and Western equine. These
viruses are normally infections of birds or small mammals. Dur-
ing such infections, the level of the virus may increase in
these infected animals facilitating transmission to humans by
mosquitoes. The West Nile virus, which can also cause encephali-
tis, was found in the northeastern United States for the first
time in 1999, is a good example of this mode of transmission.
Human cases of encephalitis range from mild to very severe ill-
nesses that, in a few cases, can be fatal. Dengue is a viral
disease transmitted from person to person by mosquitoes. It is
usually an acute, nonfatal disease, characterized by sudden on-
set of fever, headache, backache, joint pains, nausea, and vom-
iting. While most infections result in a mild illness, some may
cause the severe forms of the disease. Dengue hemorrhagic fever,
for example, is characterized by severe rash, nosebleeds, gas-
trointestinal bleeding and circulatory failure resulting in den-
gue shock syndrome and even death. Dengue is endemic in the Car-
ibbean, Central and South America. Recently, dengue has occurred
with increasing frequency in Texas. Other pathogens transmitted
by mosquitoes include a protozoan parasite which causes malaria,
and Dirofilaria immitis, a parasitic roundworm and the causative
agent of dog heartworm. Disease carrying mosquito species are
found throughout the U.S., especially in urban areas and coastal
or in inland areas where flooding of low lands frequently oc-
curs.
3. Mosquito Life Cycle [graphic omitted]
The life cycle of all mosquitoes consists of four distinct life
stages: egg, larva, pupa and adult. The first three stages occur
in water, but the adult is an active flying insect that feeds
upon the blood of humans and/or animals. The female mosquito
lays the eggs directly on water or on moist substrates that may
be flooded with water. The egg later hatches into the larva, the
elongated aquatic stage most commonly observed as it swims in
the water. The larva transforms into the pupa where internal
changes occur and the adult mosquito takes form. After two days
to a week in the pupal stage, the adult mosquito emerges onto
the water's surface and flies away. Only the female mosquito
takes blood which they usually require for her eggs to develop.
The practice of mosquito control focuses on the unique biology
and behavior of the mosquito species of concern. Mosquito biol-
ogy can follow two general scenarios. The first involves those
species that lay their eggs in masses or rafts on the water's
surface. Some of these species, which are found throughout the
U.S., often lay their eggs in natural or artificial water-
holding containers found in the domestic environment, or in
naturally occurring pools. The second scenario involves mosqui-
toes that lay their eggs on moist soil or other substrates in
areas that will be flooded with water later. After about two
days, these eggs are ready to hatch, but if not flooded, can
withstand drying for months. In inland areas of the U.S. where
these mosquitoes breed, heavy rains and flooding can produce
millions of mosquitoes in a short time. Similar situations occur
along coastal areas with mosquitoes adapted to salt marsh habi-
tats. Some salt marsh mosquitoes are strong fliers and can some-
times travel up to 50 miles from the breeding site.
4. Mosquito Control Programs
In response to these potential disease carrying pests, communi-
ties organized the earliest mosquito control programs in the
eastern U.S. in the early 1900s. Eventually, other communities
created similar programs throughout the country in areas where
mosquito problems occurred and where citizens demanded action by
local officials. Modern mosquito control programs in the U.S.
are multifaceted and include surveillance, source reduction, and
a variety of larval and adult mosquito control strategies.
Surveillance methods include studying habitats by air, aerial
photographs, and topographic maps, and evaluating larval popula-
tions. Mosquito control officials also monitor mosquito traps,
biting counts, and complaints and reports from the public. Mos-
quito control activities are initiated once established mosquito
threshold populations are exceeded. Seasonal records are kept in
concurrence with weather data to predict mosquito larval occur-
rence and adult flights. Some mosquito control programs conduct
surveillance for diseases harboured by birds, including crows,
other wild birds, sentinel chicken flocks, and for these dis-
eases in mosquitoes.
Source reduction involves eliminating the habitat or modifying
the aquatic habitat to prevent mosquitoes from breeding. This
measure includes sanitation measures where artificial contain-
ers, including discarded automobile tires, which can become mos-
quito habitats, are collected and properly disposed. Habitat
modification may also involve management of impounded water or
open marshes to reduce production and survival of the flood wa-
ter mosquitoes. If habitat modification is not feasible, bio-
logical control using fish may be possible. Mosquito control of-
ficials often apply biological or chemical larvicides, with se-
lective action and moderate residual activity, to the aquatic
habitats. To have the maximum impact on the mosquito population,
larvicides are applied during those periods when immature stages
are concentrated in the breeding sites and before the adult
forms emerge and disperse.
Some mosquitoes can fly from flood plains, coastal marsh areas,
or protected habitats to impact urban residential areas. In
these cases, it is often necessary to apply pesticides to kill
adult mosquitoes. Surveillance data may prompt insecticide ap-
plications when mosquitoes are abundant. Applications usually
coincide with the maximum adult mosquito activity in urban resi-
dential areas.
To be successful, mosquito control officials must apply insecti-
cides under proper environmental conditions (e.g., temperature
and wind) and at the time of day when the target species is most
active. They must also apply these pesticides with carefully
calibrated equipment that generates the proper-sized insecticide
droplets that will impinge on adult mosquitoes while they are at
rest or flying. If the droplets are too large, they will fall to
the ground. If they are too small, the prevailing winds will
carry them away from the target area. Once the insecticide spray
mist dissipates, they break down in the environment (generally
within 24 hours) producing little residual effect. Depending on
the situation, mosquito control officials may safely apply these
insecticides from spray equipment mounted on trucks, airplanes
or helicopters. All insecticides used in the U.S. for public
health use have been approved and registered by the EPA follow-
ing the review of many scientific studies. The EPA has assessed
these chemicals and found that, when used according to label di-
rections, they do not pose unreasonable risk to public health
and the environment.
Mosquito control officials have also developed water management
strategies that take advantage of opportunities to maximize the
impact of indigenous natural enemies to eliminate immature mos-
quitoes. The EPA and CDC encourage the use of these practices
wherever they are environmentally sound, effective, and reduce
pesticide use.
5. Integrated Pest Management
Mosquito control activities are important to the public health,
and responsibility for carrying out these programs rests with
state and local governments. The federal government assists
states in emergencies and provides training and consultation in
vector and vector-borne disease problems when requested by the
states. The current interests in ecology and environmental im-
pact of mosquito control measures, and the increasing problems
that have resulted from insecticide resistance emphasize the
need for "integrated" control programs. EPA and CDC encourage
maximum adherence to integrated pest management (IPM). IPM is an
ecologically based strategy that relies heavily on natural mor-
tality factors and seeks out control tactics that are compatible
with or disrupt these factors as little as possible. IPM uses
pesticides, but only after systematic monitoring of pest popula-
tions indicates a need. Ideally, an IPM program considers all
available control actions, including no action, and evaluates
the interaction among various control practices, cultural prac-
tices, weather, and habitat structure. This approach thus uses a
combination of resource management techniques to control mos-
quito populations with decisions based on surveillance. Fish and
game specialists and natural resources biologists should be in-
volved in planning control measures whenever delicate ecosystems
could be impacted by mosquito control practices.
The underlying philosophy of mosquito control is based on the
fact that the greatest control impact on mosquito populations
will occur when they are concentrated, immobile and accessible.
This emphasis focuses on habitat management and controlling the
immature stages before the mosquitoes emerge as adults. This
policy reduces the need for widespread pesticide application in
urban areas.
EPA and CDC recommend that professional mosquito control organi-
zations throughout the U.S. continue to use IPM strategies. Both
agencies recognize a legitimate and compelling need for the pru-
dent use of space sprays, under certain circumstances, to con-
trol adult mosquitoes. This is especially true during periods of
mosquito-borne disease transmission or when source reduction and
larval control have failed or are not feasible.
6. Education
To be of maximum effectiveness, the people, for whom protection
is provided, must understand and support mosquito control. An
integral part of most organized mosquito control programs is
public education. It is important that residents have a good un-
derstanding of mosquitoes, the benefits realized from their con-
trol and the role people have in preventing certain mosquito-
borne diseases. Being aware of pesticide application times is
also important for individuals so they may decide on precautions
they may need to take. While this usually involves education of
the public through announcements in the media, some control pro-
grams have staffs that develop and present educational programs
in public schools. People who are informed about mosquito biol-
ogy and controls are more likely to mosquito-proof their homes,
and eliminate mosquito breeding places on their own property.
7. For More Information
For more information about mosquito control in your area, con-
tact your state or local health department. The Centers for Dis-
ease Control and Prevention is a source of information on dis-
ease control, and their Internet web site includes a listing of
state health departments.
To contact the Centers for Disease Control and Prevention (CDC):
Telephone: +1-970-221-6400
Fax: +1-970-221-6476
mailto:dvbid@cdc.gov
web site: http://www.cdc.gov
Information on pesticides used in mosquito control can be ob-
tained from the state agency which regulates pesticides, or from
the National Pesticide Information Center (NPIC) West Nile Re-
source Guide http://ace.orst.edu/info/npic/wnv/
National Pesticide Information Center
1-800-858-7378 - daily except holidays. Callers outside normal
hours can leave a voice mail message.
mailto:npic@ace.orst.edu
http://npic.orst.edu/ Exit EPA disclaimer
Information on mosquito control programs can also be obtained
from the American Mosquito Control Association (AMCA) web site:
http://www.mosquito.org. Exit EPA disclaimer This site also
lists many county mosquito agencies.
For more information regarding the federal pesticide regulatory
programs, contact:
EPA Office of Pesticide Programs
Telephone: +1-703-305-5017
Fax: +1-703-305-5558
mailto:opp-web-comments@epa.gov
http://www.epa.gov/pesticides