West Nile Virus Encephalitis
Public Health Fact Sheet
Produced by the Massachusetts Department of Public Health
What is West Nile Virus (WNV) Encephalitis?
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 country. 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 percent 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 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 your
local board of health or the Massachusetts Department of Public
Health.
How common is WNV in Massachusetts?
As of Aug. 3, there have been two documented cases of WNV Encephalitis
in birds, and none in horses or humans in Massachusetts. There have been
no WNV infected mosquitoes found in Massachusetts. However, WNV has
been detected in humans and horses in New York and in birds
in New York, New Jersey, Connecticut and Maryland. It is possible that
WNV may spread to Massachusetts. 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 www.state.ma.us/dph.
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 to 15 percent for
children and with concentrations above 30 to 35 percent 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.
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
(for questions about health
effects of pesticides)
Massachusetts Department of Food and Agriculture
State Reclamation and Mosquito Control Board
(617) 626-1781
(for questions about regional
mosquito control programs)