Surveillance and Control Guidance
Article for Localities written by Trina Lee, Public Relations Coordinator for
the Virginia Department of Health's Office of Epidemiology :
"
West Nile
virus threat highlights need for local mosquito surveillance and control
programs" printed in the Virginia Municipal League�s
�Virginia Town and City� magazine, Vol. 36 No 4, April 2001.
Full text of article follows:
The birds are starting to sing and flowers are beginning
to bloom, but lurking among the beautiful signs of spring is a potential threat
to your community. Because of the recent emergence of
West Nile
virus in the
United States
, many
Virginia
localities are in need of plans for mosquito surveillance and control to
protect citizens from this virus, which may spread throughout the state as the
weather warms.
West Nile
virus is spread to birds, humans, horses and other mammals through the bite of
infected mosquitoes.
Seven crows found in
Virginia
tested positive for
West Nile
virus last year. The crows all were found in different cities and counties in
Northern Virginia
,
Central Virginia
and the Tidewater area. According to Virginia's Commissioner of Health, Dr. E.
Anne Peterson, "We would not be surprised to find more positive crows in
Virginia this year, and the potential does exist for the mosquito-borne virus
also to appear in horses and humans." No cases of
West Nile
virus have been confirmed to date in anything but birds in
Virginia
.
West Nile
virus is spread to birds, humans, horses and other mammals through the bite of
an infected mosquito. Mosquitoes become infected after biting an infected bird.
West Nile
virus is not spread from person to person, and no evidence exists that the
virus can be spread directly from birds to humans.
"Most people bitten by an infected mosquito don't get
sick. Those people who do get sick usually have a mild flu-like illness; but in
some more severe cases, people suffer from encephalitis (inflammation of the
brain) or meningitis (inflammation of the lining of the brain and spinal
cord)," Peterson said. "The elderly in the community are at highest
risk of suffering a serious illness or death from the disease."
West Nile
virus was first discovered in the
United States
in 1999 during an outbreak in
New York
. During that outbreak, 62 people suffered serious illness and seven of those
people died. In 2000, 21 became seriously ill and two of those people in the
Northeast died. Also in 2000, the virus was identified in 59 horses and six
other kinds of animals. Twenty-three of those horses died.
The human cases were confined to
New York
,
New Jersey
and
Connecticut
last year, but the virus was discovered in dead birds as far south as
North Carolina
. "The decrease in human cases between 1999 and 2000 occurred despite a
rapid geographic spread of the virus," Peterson said. "Some experts
believe the decrease was due to intensive mosquito control and prevention
efforts, which is why we are stressing the need for mosquito surveillance and
control programs in many
Virginia
localities."
Detection and prevention
The Virginia Department of Health and a number of other
agencies are working closely to detect and prevent
West Nile
virus in
Virginia
. In 2000,
Virginia
's health commissioner appointed a multi-agency team to the Virginia Interagency
Arbovirus Task Force. The task force created a plan for monitoring and reporting
West Nile
virus through the testing of dead birds, mosquitoes, horses and humans.
Also last year, the state health department received a
$178,449 grant from the U.S. Centers for Disease Control and Prevention. This
year the state received a larger federal grant of $250,884 to help improve
surveillance and laboratory capacity and to increase public awareness.
This year the state will again be testing certain birds,
mosquitoes, horses and humans for
West Nile
virus. If positive results for the virus are detected, the state health
department will first communicate that information to the health director in the
area. The health director will in turn communicate with local governmental
officials. A news release may be sent out from either the state or the local
health department to the media after officials have been notified.
"The key to preventing the spread of
West Nile
virus is to control the mosquito population," said Virginia Department of
Health Assistant State Epidemiologist Dr. Suzanne Jenkins, who chairs the task
force. Controlling the mosquitoes can involve three activities: educating the
public on eliminating mosquito breeding areas around homes, eliminating or
treating standing water on public property and spraying pesticides to kill adult
mosquitoes. "Spraying adult mosquitoes should only be used as a last
resort. A pro-active program to eliminate areas where mosquitoes breed in your
community may prevent mosquito-borne illnesses and the need for spraying down
the road," Jenkins said.
Local government planning
Local governmental officials are on the front line and
play a crucial role in protecting the public from
West Nile
virus.
"Local governments should consider now what role they
will play in preventing
West Nile
virus from spreading in their community. Because of limited resources, local
governments may want to join together and address some of these issues on a
regional basis," Jenkins said. Listed below are four ways local government
can become involved.
* Establish a local or regional mosquito surveillance
program.
* Eliminate or treat now any mosquito breeding sites.
* Develop systems for responding to citizen complaints of mosquitoes or standing
water.
* Educate citizens on
West Nile
virus and how to eliminate mosquito breeding areas.
Virginia
law gives local governments the authority to control mosquitoes through the
creation of local mosquito control districts. The district can represent one
locality or an entire region encompassing several cities, counties or towns. The
mosquito control district can manage mosquito surveillance, mosquito control,
help eliminate standing water, and conduct public education. Local governments
also can conduct these activities without establishing a mosquito control
district.
Virginia
's mosquitoes
Public Health Entomologist David Gaines is among those
monitoring
West Nile
virus for the state health department.
"Mosquitoes can breed in very small amounts of water
that is stagnant for more than five days," he said. "Some kinds of
mosquitoes breed in containers such as buckets, potted plant trays and garbage
cans and can breed in water that collects in trash, such as old tires, tin cans,
styrofoam cups and yogurt cups. Some prefer to breed in marshes, flood plains,
backed-up ditches, mud puddles and small ponds less than a foot deep with
emerging vegetation." Bodies of water that are usually not a concern for
breeding mosquitoes include permanent ponds, streams, moving bodies of water or
any water with existing fish populations.
"Approximately 60 species of mosquitoes can be found
in
Virginia
. Each mosquito has its own unique behavior and biology," Gaines said.
"Some mosquitoes feed on birds exclusively and only pass on the virus to
other birds. The kinds of mosquitoes that feed on both birds and humans or other
mammals are known as �bridge vectors.' The mosquito that poses the greatest
danger to human health is a
West Nile
virus �bridge vector' that breeds near the home and enters the home to bite
people," he said.
Several different species of mosquitoes may be a threat
for spreading
West Nile
virus in
Virginia
. Two species of concern are the Northern House mosquito (Culex pipiens) and the
Asian tiger mosquito (Aedes albopictus). The Northern House mosquito feeds
mostly on birds but will also bite people. This type of mosquito breeds in
polluted water and artificial containers often found near homes or in urban
settings. They enter homes and feed at night in the dark when people are
sleeping. The Asian tiger mosquito (Aedes albopictus) breeds in containers,
bites both birds and people and can be found around and inside the home. The
Asian tiger mosquito, which bites during the daytime, also is very common in
Virginia
.
Mosquito surveillance and control
Preventing mosquitoes from breeding begins with mosquito
surveillance.
"You need to find out what kinds of mosquitoes you're
dealing with before you can figure out where they are breeding and how and when
to control them," said Gaines, who is advising
Virginia
localities on setting up mosquito programs. "Different species of
mosquitoes breed in different habitats. Some bite during the day and some bite
only at night. Some species will only fly 100 yards, while others will fly five
miles. Some species of mosquitoes feed only on birds, and others will bite
birds, large animals and humans. All of these factors will play an important
role in developing a mosquito control program that will attack the species of
mosquitoes that are a problem," he said.
"The two most useful methods for mosquito
surveillance are traps for adult mosquitoes and dip sampling for larval
mosquitoes. Adult mosquitoes are usually trapped using battery-powered light
traps baited with CO2," Gaines said. "The traps are generally set up
on a regular schedule at designated areas, but may be moved around to
investigate potential problem areas. Once a local mosquito species is
identified, you can usually determine the source of the mosquito based on its
breeding and flight habits."
Larval surveillance using a dipper cup helps to identify
new or suspected breeding areas or to regularly monitor mosquito populations in
identified breeding habitats. Collected larvae can be identified to determine
which species are present. Dip sampling also will help determine the number of
mosquitoes in an area and if a larvicide treatment is necessary.
Mosquito control should focus on areas that are close to
neighborhoods. According to Gaines, mosquito control is not cost effective or
efficient in rural areas, because the human population is relatively small and
many of the mosquitoes breed on private land.
One method of controlling mosquitoes on public property is to drain unnatural
and stagnant water areas, such as clogged ditches and puddles. If a mosquito
breeding area cannot be drained, recommended larvicides used regularly can help
eliminate mosquitoes before they become adults. "Adult mosquito control
methods, such as spraying or fogging, can be used against mosquitoes that have
escaped larval control or for areas that are too large or inaccessible for
applying larvicide," Gaines said.
If spraying for adult mosquitoes becomes necessary, having a plan already in
place for how citizens will be notified can save time. "You'll want to
decide now how you're going to quickly get that information out to citizens who
could be affected by the spraying. The public will want to know in advance when
and where the spraying will take place and what precautions to take,"
Jenkins said.
Public education
Public education is an important tool in combating
West Nile
virus, because the types of mosquitoes most likely to carry it are those that
breed in containers found around the home. A big part of the battle to control
mosquitoes lies with community residents.
The Virginia Department of Health is kicking off a
statewide awareness campaign this spring to educate the public about
West Nile
virus. The campaign will include information on eliminating mosquito breeding
areas, using insect repellent safely, wearing protective clothing and reporting
dead birds. The state health department will be sending out a news releases,
placing radio and television public service announcements throughout
Virginia
and conducting other public information activities.
"Citizens need to know how to prevent mosquitoes from breeding in their
yards by turning over or removing containers that collect rainwater such as old
tires, potted plant trays, boats, buckets and toys. Birdbaths and wading pools
should be cleaned once a week," Jenkins said. "Roof gutters and
downspout screens should be cleaned regularly and standing water should be
eliminated on flat roofs."
"We also want to encourage the public to properly
protect themselves from mosquitoes when they are outside by wearing long, loose
and light colored clothing. They should follow label instructions when using
insect repellent. The repellents for adults should contain no more than 20 to 30
percent DEET and less than 10 percent for children," Jenkins said.
The public can help state officials monitor for the virus
by reporting all dead birds to their local health department. The state will
compile data on the number of dead birds reported. Only selected crows, blue
jays and raptors (i.e. hawks, falcons or owls) will be tested for the virus,
because those species are the best indicators of the virus. Birds must be tested
within 24 hours of death before they decompose. Sunken eyes and presence of fly
larvae (maggots) are good indicators that the bird has been dead too long.
"City and county governments also will want to
incorporate public awareness and education into their overall mosquito
surveillance and control program, because they have more direct contact with
citizens," Jenkins said. "Localities are already in the process of
communicating with citizens on several issues, such as crime and water quality.
Now is the time to incorporate
West Nile
virus into your public awareness plans."
In
Brookline
,
Mass.
, the local government hung doorknob flyers with mosquito control tips on the
front doors of every home. In
Montgomery County
,
Md.
, the health department sent out a chain e-mail on
West Nile
virus to every county employee asking everyone to forward the e-mail message.
Some cities or counties have sent out information to the public in their water
and sewer bills.
Local public awareness campaigns should include
information on how citizens can report standing water or mosquito complaints to
the local government. When the disease was first discovered,
New York City
officials set up an 800-hotline number for citizens to report standing water.
"Taking reports from citizens is a great way to help detect potential
mosquito breeding areas. You also can expect that some citizens will want to
know how the local government plans to deal with a particular problem,"
Gaines said.
Resources
A number of state and local resources are available to
help coordinate plans for a mosquito surveillance and control program.
Localities can start by contacting their local health director to help
coordinate planning. David Gaines, the state health department's public health
entomologist, is available to advise localities on establishing a mosquito
program. Assistant State Epidemiologist Dr. Suzanne Jenkins is available to
assist with medical questions regarding
West Nile
virus. Public Relations Coordinator Trina Lee is available to advise localities
on media issues and public education. Gaines, Jenkins and Lee can be contacted
by calling the Virginia Department of Health's Office of Epidemiology at
804/786-6261.
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