The Carlisle Mosquito Online

Friday, October 6, 2000


More about West Nile Virus

The following is a public health fact sheet issued by the Massachusetts Department of Public Health.

What is West Nile Virus (WNV) Encephalitis?

West Nile virus (WNV) encephalitis is a rare disease caused by a virus. In a small percentage of people infected by the virus, the disease can be serious, even fatal. The virus that causes WNV encephalitis occurs in Europe, Africa and Asia. It was first identified in the United States during the summer of 1999. It is not known how WNV got to the U.S. WNV grows in birds, and it is transmitted from bird to bird and from birds to humans by mosquitoes. Horses bitten by mosquitoes carrying WNV can also become sick.

What are the symptoms of WNV Encephalitis?

Mild WNV infections cause fever, headache and body aches, often with a skin rash and swollen lymph glands. More severe infections can cause headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, paralysis and, sometimes, death.

Is there treatment for WNV Encephalitis?

There is no treatment for WNV infection. Doctors can treat the symptoms of WNV encephalitis. However, about 7% of people who become sick enough from the infection to be hospitalized die from it.

How is WNV spread?

WNV is spread only by adult mosquitoes that are infected with the virus. People and horses that have WNV infection cannot spread the disease without mosquitoes. The risk of getting WNV encephalitis is highest from late July through September. There is no evidence that a person can get WNV from handling live or dead infected birds. Still, you should avoid bare-handed contact when handling dead animals, including birds. If you must handle dead birds, use gloves or double plastic bags. If you notice unusual numbers of dead birds in your area, call your local board of health or the Massachusetts Department of Public Health.

How common is WNV in Massachusetts?

Until recently, there have been no documented cases of WNV encephalitis in birds, horses, or human residents of Massachusetts. On July 26, 2000, a bird from Boston was found to be infected with WNV. The mosquitoes that carry this virus are common throughout the state, and these mosquitoes are found in the city as well as in the woods and other less populated places. For up-to-date information on West Nile virus in Massachusetts, visit the Massachusetts Department of Public Health's web site at

What can you do to protect yourself?

There is no vaccine for WNV. The only way to protect yourself is to keep mosquitoes from biting you. Follow these steps every summer if you live in or visit an area with mosquitoes:

· Avoid outdoor activities between dusk and dawn, if possible, as this is the time of greatest mosquito activity.

· If you must be outdoors when mosquitoes are active, wear a long-sleeved shirt and long pants. Use a mosquito repellent that contains DEET (the chemical N-N-diethyl-meta-toluamide) and follow the directions on the label. DEET can be poisonous if overused. Never use DEET on infants. Avoid using repellents with DEET concentrations above 10-15% for children and with concentrations above 30-35% for adults. Cream, lotion or stick formulas are best. Avoid products with high amounts of alcohol.

· Take special care to cover up the arms and legs of children playing outdoors. When you bring a baby outdoors, cover the baby's carriage or playpen with mosquito netting.

· Fix any holes in your screens and make sure they are tightly attached to all your doors and windows.

What can you do to reduce the number of mosquitoes around your home and neighborhood?

To reduce mosquito populations around your home and neighborhood, get rid of any standing water that is available for mosquito breeding. Mosquitoes will breed in any puddle or standing water that lasts for more than four days. Here are some simple steps you can take:

· Dispose of or regularly empty any metal cans, plastic containers, ceramic pots and other water holding containers (including trash cans) on your property.

· Pay special attention to discarded tires that may have collected on your property. Tires are a common place for mosquitoes to breed.

· Drill holes in the bottom of recycling containers that are left outdoors, so that water can drain out.

· Clean clogged roof gutters; remove leaves and debris that may prevent drainage of rainwater.

· Turn over plastic wading pools and wheelbarrows when not in use.

· Do not allow water to stagnate in birdbaths; aerate ornamental ponds or stock them with fish.

· Keep swimming pools clean and properly chlorinated; remove standing water from pool covers.

· Use landscaping to eliminate standing water that collects on your property.

What is Massachusetts doing to protect people from WNV?

The Massachusetts Department of Public Health (MDPH) has had a long-standing program to look for another virus carried by mosquitoes, Eastern Equine Encephalitis virus. Every year from May until the first frost, MDPH field staff collect mosquitoes and bring them to the State Laboratory for testing. MDPH has expanded this mosquito surveillance program to look for WNV throughout Massachusetts. Under this expanded program, mosquito collections will be increased and more sites will be sampled. Also, a system is in place to test dead birds to look for the presence of WNV. The State Laboratory can also test for WNV infection in horses and humans. If WNV is detected in Massachusetts, MDPH will alert local boards of health, hospitals, and people who live in the area.

2000 The Carlisle Mosquito