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From the Occupational and Community Health Directorate
West Niles Virus (WNV) is a virus that has recently been introduced into
North America. It can lead to encephalitis. The transmission cycle for WNV is
not fully understood. Over the winter the virus may survive in birds or
hibernate in adult mosquitoes, to become a problem again when the weather warms.
For this reason, surveillance of both adult mosquitoes and birds will greatly
enhance early detection.
Most people who are infected have no symptoms or may experience mild illness
such as fever, headache, and body aches, with skin rash and swollen lymph
glands. Symptoms usually occur five to 15 days following the bite of an infected
mosquito. In the most serious cases, there can be rapid onset of severe
headache, high fever, stiff neck, disorientation, muscle weakness, coma, and
rarely, death. Individuals over the age of 50 have the highest risk of severe
infection.
While many birds are not susceptible to WNV, others are. This was seen
last fall when at least 18 native birds, including the American crow were
infected with WNV. The major vector for WNV last year was Culex pipiens
also known as the house mosquito. The house mosquito most often breeds in
containers around homes and buildings that hold dirty and stagnant water
(e.g., birdbaths, buckets, pots, gutters, pool covers etc). Several
hundred eggs are laid in rafts and a female can lay six or seven times in
her 40- to 50-day life span. The house mosquito mainly feeds on wild
birds, but can also feed on a variety of warm-blooded vertebrates,
including humans. It bites frequently during dawn, dusk, the early evening
and throughout the night. The mosquito can acquire the virus when it bites
an infected bird. If the same mosquito subsequently (10 days to two weeks
later) bites a human, it can pass the virus to the human.
What can be done?
To reduce breeding sites at home:
* Dispose of tin cans, plastic containers, ceramic pots, or similar liquid
holding containers from areas where water may accumulate.
* Do not overlook containers that have become overgrown by aquatic
vegetation.
* Pay special attention to tires that may accumulate water.
* Drill holes in the bottom of recycling containers that are left out of
doors.
* Clean clogged roof gutters on an annual basis.
* Turn over plastic wading pools when not in use.
* Turn over wheelbarrows and do not allow water to stagnate in bird baths.
* Aerate ornamental pools or stock them with fish.
* Clean and chlorinate swimming pools that are not being used.
* Use landscaping to eliminate standing water.
To protect yourself:
* Stay indoors at dawn, dusk, and in the early evening.
* Wear long-sleeved shirts and long pants whenever you are outdoors.
* Apply insect repellent to exposed skin. An effective repellent will contain
20 percent to 35 percent DEET (N-DIETHYL-METATOLUAMIDE). P < DEET. percent 35
than more containing products avoid children; in particularly effects, side
cause may percent) (greater concentrations high DEET>
* Repellents may irritate the eyes and mouth, so avoid applying repellent to
the hands of children. Insect repellents should not be applied to very young
children (under 3 years old).
* Spray clothing with repellents containing permethrin or DEET, as mosquitoes
may bite through thin clothing.
* Whenever you use an insecticide or insect repellent, be sure to read and
follow the manufacturer's directions for use, as printed on the product
Note: Vitamin B and "ultrasonic" devices are not effective in
preventing mosquito bites.
If you find dead crows or birds at home please contact your local health
department who will send a representative to pick up the bird or request you
dispose of the bird in an appropriate manner. While it is not likely that a
person can get WNV from m handling live or dead birds, people should always
avoid barehanded contact with dead animals. Hands should also be washed with
soapy water after handling dead animals even if gloves or plastic bags are used.
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