Vector Borne Illness Prevention Program: Mosquito Information & Prevention
The Asian Tiger Mosquito (Aedes albopictus) is the number one nuisance species found in the city. It is a black mosquito with striking white markings on its body and legs. The Asian Tiger Mosquito is a very aggressive day biting mosquito. They prefer to bite humans and breed in artificial containers, such as tires, buckets, flowerpots, and corrugated drainpipes, that hold water for five days or more. They do not travel far from their breeding site and rest anywhere it is cool, humid and shady. Ivy and azaleas or other bushes are among their favorite resting places. The Asian Tiger Mosquito can transmit West Nile virus, but they are not very good at it. (photo courtesy of Sean McCann. © 2006)
Culex mosquitoes (Culex pipiens and Culex restuans) are the most important mosquitoes in the West Nile virus transmission cycle. Even though they prefer to feed on birds, they will bite humans and other mammals, which can get sick if they become infected. Small brown mosquitoes, they are not aggressive feeders, preferring to feed during dusk and dawn. Because they are not as aggressive as other mosquitoes, you may not notice when one is biting you – another good reason to wear insect repellent. Culex mosquitoes breed in stagnant, organic, nutrient-rich water. Places like catch basins (storm drains), clogged rain gutters and sites where water stands for a longer period of time (a few weeks).
There are four stages in the life of a mosquito: egg, larva, pupa, and adult. Mosquitoes MUST have standing water to complete their life cycle.
- Mosquito eggs are laid so they hatch in water, generally not in moving water or water with aquatic life (fish, frogs)
- Larvae feed and grow in the water for about one week
- A larva turns into a pupa, which is also found in the water, but does not feed
- Inside the pupa, an adult mosquito develops and emerges into the familiar flying form
- Female mosquitoes bite because they need blood to provide nutrients for their eggs
- A female mosquito will lay 200-300 eggs each time she has a blood meal. She may lay eggs three or four times during the month that she is alive.
West Nile Virus
West Nile virus (WNV) is a virus that is transmitted to people by the bite of an infected mosquito. Symptoms generally appear three to 15 days after being bitten by an infected mosquito. While everyone is equally susceptible to WNV, immunocompromised individuals and people over the age of 50 are at greatest risk for developing more severe forms of the disease. Currently, no vaccine against WNV is available for people.
WNV in Alexandria
Each year, the Health Department traps and tests mosquitoes for WNV. These traps are located at numerous sites around the City in areas where mosquitoes have been observed. Typically, the Health Department will identify infected mosquitoes in July or very early August.
The natural transmission cycle of WNV is between a few species of mosquitoes and birds. Very few mosquitoes actually transmit the virus.
- An infected bird is bitten by a mosquito
- The mosquito picks up the virus from the bird
- After a week, the mosquito can transmit the virus the next time it feeds
- The infected mosquito feeds on an uninfected bird; the virus is transmitted to the bird and the WNV cycle continues.
- Sometimes, the infected mosquito will feed on humans or horses. Some of these humans and horses can get sick or die from the infection.
Signs and Symptoms
Approximately, 80% of people who are infected with WNV will not have any symptoms of illness at all. Symptoms usually appear three to fifteen days after a person is bitten by an infected mosquito.
Mild symptoms: Up to 20% of the people infected with WNV develop WNV fever. Symptoms may include fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach, and/or back. Symptoms may last for a few days to several weeks.
Serious symptoms: About one in 150 people develop severe illness. This may include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, or paralysis. These symptoms may last several weeks and neurological effects may be permanent. West Nile virus infection can be fatal.
Protection and Prevention
What can you do to "Fight the Bite!"?
- Wear long, loose, and light-colored clothing to avoid mosquito bites
- Choose and use a repellent that contains one of these active ingredients: DEET, Picaridin, oil of lemon eucalyptus, or IR-3535 (a biopesticide).
The best repellent is one that you will actually use.
- DEET-based repellents are available in various concentrations that repel insects equally well for the length of time needed. DEET has provided, effective, dependable protection since the 1950s. DEET is the most effective and best-studied repellent available.
- Picardin is a synthetic repellent developed in the 1990s. It is colorless, nearly odorless, and is available in multiple formulations. It provides long-lasting, effective protection similar to identical concentrations of DEET. Be advised that neither the manufacturers nor the CDC have issued specific recommendations regarding the use of Picardin on children.
- IR-3535 (Merck 3535) is registered as a biopesticide. Approved for use in the USA in 1999, it has been used in Europe for 20 years.
- Oil of Lemon Eucalyptus is a natural plant-based repellent. Products containing oil of lemon eucalyptus provide protection similar to low concentrations of DEET.
All of these products are available in a wide variety of forms including aerosol and pump sprays, and wipes.
Flower Pot Collecting Water
Bird Bath Collecting Water
Corrugated Pipe Collecting Water
Clogged Gutter with water
Defend your garden! To get rid of adult mosquitoes around your home, follow these tips.
Once a week
- Empty any water from free-standing containers, such as flowerpot saucers, watering cans, and buckets
- Change the water and clean bird baths with a garden hose
- Empty water that collects in the folds of tarps used to cover woodpiles, boats, pools, etc.
- Position corrugated drainpipes to ensure drainage
Once a month
- Apply a larvicide (an insecticide applied to water to kill mosquito larve), such as Mosquito Dunks®, to standing water that cannot be emptied or drained.
- Clean leaves and debris from roof gutters.
- Recycle old tires
- Be sure water on property flows freely from drainage areas
- Fill-in puddles or areas of your yard that remain wet and soggy for more than a week
- Aerate ornamental ponds or stock the pond with fish
- Apply a barrier spray to vegetation around your home. Products containing the active ingredient permethrin will provide two to three weeks of relief from biting adult mosquitoes.
Always follow label instructions.
What the Health Department is Doing
The Alexandria Health Department's Vector-borne Illness Prevention Program is doing the following things to protect the public from mosquito-borne disease:
- Trapping adult mosquitoes using numerous permanent adult mosquito trap sites throughout the city. These efforts allow us to monitor mosquito populations around the city.
- Testing the mosquitoes collected in our traps for West Nile virus so we can estimate the risk of mosquito-borne disease transmission.
- Responding to areas identified as having a higher-risk of disease transmission with increased surveillance, larvicide treatments, and/or community outreach.
- Proactively inspecting and larviciding storm drains. These areas are then recorded and mapped and are regularly treated to kill mosquito larvae.
- Providing residents and businesses assistance with mosquito problems
- Setting up educational displays at various local events and festivals to promote effective mosquito control
- Giving presentations for various civic associations and communities
- Investigating complaints about mosquitoes made by local residents
Adult mosquito traps used in the city.
Vector-Borne Illness Prevention Program
Environmental Health Division
Alexandria Health Department
4480 King Street, Rm 361
Alexandria, VA 22302
Phone: 703.746.4910 (ask about mosquitoes)
Hours: 8 a.m. to 4:30 p.m. (M,Tu,W,F) and 1:30 p.m. to 4:30 p.m. (Th)
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