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.