West Nile Virus (WNV) is a
mosquito-borne virus that can cause encephalitis or meningitis-- an
inflammation of the brain -- in humans and other animals. People get
West Nile
from the bite of a mosquito that is infected with
West Nile
virus. Mosquitoes become infected with
West Nile
virus when they feed on infected birds that carry the virus in their blood.
West Nile
virus is NOT transmitted from person to person. For example, you cannot get
West Nile
virus from touching or kissing a person who has the infection.
West Nile
virus is closely related to two other mosquito-borne encephalitis viruses in
the
United States
: St. Louis Encephalitis (SLE) and Eastern Equine Encephalitis (EEE). These
viruses have been responsible for illnesses requiring hospitalization of over
a hundred people in
Michigan
, with several deaths. Some of
these viruses have also caused equine illness with over 200 horse deaths
confirmed.
Michigan
's history of mosquito-borne disease can be traced back before the arrival of
the European settlers in the early 18th century. However it wasn't until 1858
that the first documented mosquito-borne disease outbreak was identified. This
occurred at the
Michigan
Agricultural
School
(now
Michigan
State
University
) where 70 students were diagnosed with malaria. Since that time,
Michigan
's history of mosquito-borne diseases has involved three separate concerns:
malaria, dog heartworm, and encephalitis [St. Louis Encephalitis (SLE),
Eastern Equine Encephalitis (EEE), and the California Group].
Locally acquired cases of
malaria are rare in
Michigan
, but are still of potential concern because the disease is reintroduced each
year by travelers and immigrants. Dog heartworm was first identified in
Michigan
during the early 1960's. It is currently found in the continental
United States
and in every county in
Michigan
's lower peninsula.
It is of greater importance as a veterinary concern than as a human
health threat.
It wasn't until the 1930's
that scientific methods were able to discover mosquito-borne encephalitis
viruses. EEE, SLE, and California Group viruses have been responsible for
diseases requiring hospitalization of over a hundred people in
Michigan
, with several deaths. Some of these viruses have also caused equine disease
with over 200 confirmed horse deaths.
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West Nile Virus was first
discovered in
Uganda
,
Africa
, in 1937. The virus was then found in humans, birds, and other animals in
Africa
, West and
Central Asia
, and the
Middle East
. It is not known how
West Nile
virus was introduced to the
United States
, nor how long it has been here. Scientists from
the Centers for Disease Control and Prevention believe the virus probably
entered the eastern
United States
during early summer of 1999, when
New York City
experienced numerous illnesses and deaths related to the virus. Since entering
the
United States
, the virus has spread rapidly across the country. From 1999 through 2001, a
total of 149 human cases of West Nile Virus had been detected in the
United States
, resulting in 18 deaths. In 2002, 644 human cases and 51 human deaths
occurred in
Michigan
alone.
The first infected bird in
Livingston
County
was detected in the summer of 2001. Since
then, the virus has been detected in more birds, but no human cases have yet
occurred in
Livingston
County
.
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Mosquitoes become infected
with WNV when they feed on infected birds, which may circulate the virus in
their blood for a few days. Infected mosquitoes can then transmit West Nile
Virus to humans and animals while biting to take blood. The virus is located
in the mosquito's salivary glands. During blood feeding, the virus may be
injected into the animal or human, where it may multiply, possibly causing
illness. Click
here to see an image of the West Nile
Virus transmission cycle.
The virus attacks the central nervous system and can weaken the immune
system and muscles. Once the virus is in the bloodstream, it can multiply and
inflame brain tissue, which can lead to encephalitis or meningitis.
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The risk of getting
West Nile
encephalitis is limited to persons in areas where virus activity occurs, and
the risk is higher in persons older than 50 years of age or in persons with
compromised immune systems. The
chances you will become severely ill from any one mosquito bite are extremely
small. Even in areas where mosquitoes do carry the virus, very few
mosquitoes—much less than 1%—are infected.
Eighty percent of people who become infected with West Nile Virus
experience no symptoms. Only 20% of those infected will experience mild
flu-like symptoms such as sore throat, fever, lymph node swelling, headache,
vomiting, abdominal pain, conjunctivitis, and/or rash. This mild illness is
termed West Nile Fever. Less than
1% of people who get bitten and become infected with West Nile Virus will
develop a severe illness like encephalitis or meningitis.
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Most people infected with
West Nile
virus have no symptoms of illness, but some may become ill 3-15 days after the
bite from an infected mosquito. Studies have shown that about 1 in 4 infected
persons will experience mild illness with fever, headache, and body aches,
sometimes with a skin rash and swollen lymph glands. More severe infection
(encephalitis) is less common and may be marked by headache, high fever, stiff
neck, disorientation, convulsions, muscle weakness, and paralysis. In a few
cases, mostly among the elderly, death may occur.
Persons with symptoms of
encephalitis or meningitis should seek medical attention immediately.
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There is no specific treatment
for West Nile Virus. In more severe cases, intensive supportive therapy is
needed, including hospitalization, intravenous (IV) fluids, respiratory
support, prevention of secondary infections, and good nursing care.
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There is no vaccine currently
available for West Nile Virus. However, you can reduce the risk of becoming
infected in these ways:
 |
Avoid activities in areas where large numbers of mosquitoes are
present. |
|
Wear long-sleeved shirts and long pants whenever in areas with
large numbers of mosquitoes. |
|
Apply insect repellent to exposed skin and clothing when in
areas with large numbers of mosquitoes. Avoid applying repellent to children
under 2 years of age, and to the hands of older children. |
|
Maintain window and door screens to keep mosquitoes out of
buildings. |
|
To limit breeding sites for mosquitoes, drain standing water in
your yard. Empty standing water from flower pots, clogged rain gutters,
swimming pool covers, discarded tires, buckets, plastic wading pools, and
similar items that can collect water in which mosquitoes can lay eggs. Keep
swimming pools, wading pools, and bird baths clean and filled with fresh
water.
|
In addition,
Livingston
County
will be encouraging local municipalities to participate in larviciding
activities during the summer of 2003. Larviciding
involves placing materials harmful to mosquito larvae into storm drains, catch
basins, and other standing water sites. This
procedure dramatically reduces the number of mosquito larvae, thereby reducing
the number or adult mosquitoes that are able to transmit the virus. Contact
your local municipality for more information on their mosquito control plans.
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Federal, state, and local
governments, along with other non-governmental organizations, are conducting
disease monitoring efforts for
West Nile
virus infections among mosquito, bird, horse, and human populations.
West Nile Virus was first
detected in
Michigan
in August 2001. The virus was found in dead crows and mosquitoes; no human
cases were detected. Human cases
were detected in 2002. Bird surveillance during the summer of 2003 will
include testing of dead birds. Once a particular zip-code has tested positive,
no more birds will be accepted from that zip-code area. Mosquito trapping and
surveillance for
West Nile
virus (WNV), St. Louis Encephalitis (SLE), and Eastern Equine Encephalitis (EEE)
will also occur. Active
surveillance of suspect horse and human cases will be conducted in
collaboration with physicians and veterinarians across the state.
Data from mosquitoes, birds,
and veterinary cases are being collected and reported on a weekly basis. Go to
the State of
Michigan
’s website at www.michigan.gov/westnilevirus
to view the latest information, data and area maps on West Nile Virus
Activity.
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In the past few years, a
connection was made between an outbreak of human
West Nile
virus infection and disease in the corvid species
of birds (specifically crows, blue jays and ravens). Crows, blue jays and
ravens appear to be very susceptible to the virus, and usually die within two
weeks of becoming infected. Currently,
the best indicator of
West Nile
virus activity in an area is the presence of these dead birds.
As part of the monitoring
effort, citizens are asked to report dead birds to the State of
Michigan
. This can be done by one of the
following means:
|
Call the Livingston County Department of Public Health directly
at 517.546.9858. |
|
Call the State of
Michigan
’s West Nile Virus
Toll-Free Hotline
at 888.668.0869. |
|
Use the State of
Michigan
’s Web-Based Reporting System at www.michigan.gov/westnilevirus
|
There is no evidence that a
person can get the virus from handling live or dead infected birds. However,
persons should avoid bare-handed contact when handling any dead animals. If
the dead bird must be handled, wear disposable rubber gloves or use a plastic
shopping bag to scoop up the bird. Dead
birds should be placed in a double plastic bag and disposed of in the outdoor
trash.
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The purpose of the mosquito
surveillance is to identify species of mosquitoes carrying WNV, quantify
mosquito numbers, determine the proportion of which species are infected and
make an assessment of potential human risk.
In conjuction with the Michigan Department
of Agriculture, the Livingston County Department of Public Health has been
trapping and testing mosquitoes for SLE and EEE for the past 10 years. This
year the State will also be testing mosquitoes for
West Nile
virus. From July through
September, live mosquitoes will be collected and tested on a weekly basis by
LCDPH personnel.
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Although the vast majority of
infections have been identified in birds, the national Centers for Disease
Control and Prevention has received reports of West Nile virus infection in
horses, cats, bats, chipmunks, skunks, squirrels, domestic rabbits, and
raccoons. Common household pets, such as dogs and cats, are unlikely to suffer
from serious illness due to West Nile Virus infection.
Talk to your veterinarian if you are concerned about your pet becoming
infected. Also, you can visit the
USGS
National
Wildlife
Health
Center
website
for more information on West Nile Virus in other animals.
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