Public Health Study Warns About the Long-Term
Effects of West Nile Virus
Second mosquito pool confirmed positive
July 18, 2006, Boulder, CO — Just as Boulder County Public Health (BCPH)
and Tri-County Health Department (TCHD) publish a study revealing the
considerable extent and ongoing harmful effects of the disease, the
second mosquito pool for 2006 is confirmed positive for West Nile
virus (WNV) in Boulder County.
The study, published this month in Emerging Infectious Diseases, the
monthly journal of the Centers for Disease Control and Prevention
(CDC), also discusses the substantial economic impact in terms of
healthcare costs and days of missed work.
The agencies state that the study should serve as an important warning
as we enter the height of West Nile virus season. Recent heavy rains
and hot summer temperatures have produced the perfect breeding
conditions for mosquitoes that might carry West Nile virus. “Now with
the second positive West Nile virus mosquito pool in the county,
residents really must take steps to protect themselves,” said Heath
Harmon, a BCPH epidemiologist.
The two agencies collaborated on a follow-up study of all hospitalized
West Nile virus cases reported in their counties in 2003. That year,
Colorado experienced the largest West Nile virus epidemic ever
recorded in the U.S., with 2,947 confirmed human cases and 63 deaths.
This accounted for 29.9% of the nation's 9,862 reported cases.
A total of 656 patients who were infected with West Nile virus
completed the survey. Of these, 80.9% had a diagnosis of West Nile
virus fever, 12.8% had a diagnosis of meningitis (inflammation of the
brain's lining), and 6.3% had a diagnosis of encephalitis
(inflammation of the brain). Though West Nile virus fever had
previously been classified as a “mild illness,” this study found that
20% of patients with a WNV fever diagnosis had symptoms for three
months or longer.
The study reveals that missing time from work was common, ranging from
a median of 65 days among encephalitis patients to a median of 16 days
for fever patients. In addition, 91% of all patients reported that
their routine daily activities were prevented by their WNV infection.
A recent Colorado survey also revealed that the vast majority of
people who get West Nile virus are bitten by infected mosquitoes from
around their own homes. “These findings should serve as a reminder to
people that they need to use insect repellent to protect themselves
from mosquito bites every time they are outdoors … whether it’s in the
backwoods or in the backyard,” said Harmon.
Mosquitoes lay their eggs in standing water, and the larvae hatch in 7
to 10 days. Mosquito breeding is not limited to ponds and streams, so
eliminating even small amounts of standing water around the house on a
weekly basis is a good prevention measure. Common household items that
can hold enough water for mosquitoes to breed include flowerpots and
saucers; clogged rain gutters; tires and tire swings; sandbox toys;
tin cans; and jars. Pet water bowls should be cleaned daily, and
birdbaths and wading pools should be hosed out weekly.
Recommended mosquito precautions include the five D’s:
-
DRAIN all standing water around the house to eliminate any
mosquito-breeding sites.
-
DRESS in long-sleeved shirts, long pants, shoes, and socks.
-
Avoid outdoor activities at DUSK and DAWN when mosquitoes are most
active.
-
Use mosquito repellents that contain DEET while outdoors.
In addition to DEET, the CDC and the Environmental Protection Agency
have approved two new ingredients for use in insect repellents -
picaridin and oil of lemon eucalyptus.
West Nile virus is carried long distances by infected birds and is
then spread locally by mosquitoes that bite these birds. Infected
mosquitoes can then bite and pass the virus to humans. House pets do
not become ill if bitten and do not spread the illness. There is also
no human-to-human transmission by someone who already has the virus.
Most infections are mild, and symptoms can include fever, headache,
body aches, skin rashes, and swollen lymph nodes. Symptoms usually
appear 3 to 14 days after exposure. All residents of areas where West
Nile virus activity has been confirmed are at risk, but people over
age 50 seem to be especially vulnerable to the most severe forms of
disease.
Signs of more severe illness may include headache, high fever, neck
stiffness, stupor, disorientation, coma, tremors, muscle weakness, or
convulsions. Persons with these symptoms should seek medical attention
immediately, because West Nile virus can also cause paralysis,
encephalitis, and/or meningitis. In some cases, it can be fatal.
Additional information:
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