West Nile Virus

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 United States. WNV grows in birds, and it is transmitted from bird to bird and from birds to humans by mosquitoes (primarily the culex species). 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.

How is WNV spread?

WNV is spread only by adult mosquitoes (primarily the culex species) 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 barehanded 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 the Norwell Board of Health or the Massachusetts Department of Public Health.

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 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-metatoluamide) 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 or 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.

West Nile Virus Hotline: 866-627-7968

If you discover a dead bird on your property, call the Public Health Hotline before you call Animal Control. Follow their instructions. The Animal Control Officer will assist you if requested by the Mass. Department of Public Health. If no testing is required, dispose of the bird by throwing it in the woods near your residence, or in our household trash. Dead animals on private property are the responsibility of the property owner.

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.

For more information:

Massachusetts Department of Public Health
Division of Epidemiology and Immunization (617) 983-6800
(for questions about WNV and consultations for health care providers and hospitals on WNV)
Bureau of Environmental Health Assessment (617) 624-5757
To report dead birds: 1-866-MASS WNV (1-866-627-7968)

Massachusetts Department of Food and Agriculture
State Reclamation and Mosquito Control Board (617) 626-1781
(for questions about regional mosquito control programs)

Plymouth County Mosquito Control Project
(781) 585-5450

Norwell Board of Health
(781) 659-8016
Brian T. Flynn, RS, Health Agent
R. Benjamin Margro, Administrative Assistant