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What
is West Nile Virus?
West Nile is a mosquito-borne virus that can cause encephalitis
(inflammation of the brain) or meningitis (inflammation of the lining of the
brain and spinal cord). It is a flavivirus
commonly found in Africa, West Asia, and the Middle East.
Most
infections with West Nile virus have been identified in wild birds, but the
virus can also infect humans, horses, dogs, cats, bats, chipmunks, skunks,
squirrels, domestic rabbits, and domestic birds.
Most
people who become infected with West Nile virus will have either no symptoms or
only mild ones. However, on rare occasions, West Nile virus infection can result
in severe and sometimes fatal illnesses.
There
is no evidence to suggest that West Nile virus can be spread from person to
person or from animal to person.
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What
is West Nile Fever?
“West
Nile fever” is a case of mild disease in people, characterized by flu-like
symptoms. West Nile fever typically lasts only a few days and does not appear to
cause any long-term health effects.
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What
is West Nile Encephalitis?
More severe disease due to a person being infected with this virus can be
“West Nile encephalitis,” “West Nile meningitis” or “West Nile
meningoencephalitis.” Encephalitis refers to an inflammation of the brain,
meningitis is an inflammation of the membrane around the brain and the spinal
cord, and meningoencephalitis refers to inflammation of the brain and the
membrane surrounding it.
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Where
did West Nile virus come from?
West
Nile virus was first
isolated in 1937 in the West Nile district of
Uganda. Outbreaks of West Nile virus have
occurred in a number of countries including Egypt, Israel, South Africa, and
countries in parts of Asia and Europe. Recent outbreaks, outside of North
America, have occurred in France and Israel in 2000, Russia in 1999, and Romania
in 1996-97.
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How
long has West Nile virus been in the U.S.?
It
is not known how long it has been in the U.S., but CDC scientists believe the
virus has probably been in the eastern U.S. since the early summer of 1999,
possibly longer.
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How
West Nile spread?
West Nile virus is spread to human by the bite of an infected
mosquito. A mosquito becomes infected by biting a bird that carries the virus.
That
means, the
primary carriers of West Nile Virus are birds. Mosquitoes pick up the virus from
birds and then pass it to humans and other animals through their bites.
The Culex
pipiens or common household mosquito
spreads the virus when it feeds on a blood meal from infected birds. Scientists
believe that the most likely "reservoir" for the virus in
North
America is the common sparrow, which can tolerate the infection. Among birds,
the virus has had the greatest impact among crows. In 1999, in the New York
area, the crow population crashed by about 90 per cent in a few months.
Ten days to two
weeks after the initial blood meal, the West Nile virus reaches the mosquito's
salivary glands and can then be transmitted to birds, animals or humans.
There
is no documented evidence of animal-to-animal or animal-to-person transmission
of West Nile virus. Nor is there
evidence that a human can contract the West Nile virus by handling infected birds.
Scientists believe the
human immune system prevents the virus from multiplying in large numbers. That
prevents humans from transmitting the virus to mosquitoes.
Suspect
cases of human-to-human transmission through organ transplantation or blood
transfusions have recently been reported.
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How
dangerous is West Nile virus?
The U.S. Center for
Disease Control says that in regions where the virus is present, fewer than one
percent of mosquitoes carry it; and fewer than one percent of people bitten by
an infected mosquito will develop serious symptoms of the disease. Many people
show no symptoms.
A study in Egypt reported that
50 per cent of the people
exposed to the virus developed antibodies but showed no symptoms. However, other
people, especially the elderly and those with weakened immune systems, can
become very ill.
In 1999, 62 cases
of severe disease, including six deaths, occurred in the New York area. A
75-year-old man died in Toronto after contracting the disease in New York. In
2000, 21 cases were reported, including two deaths in the New York City area.
According
to latest information of CDC (Centers for Disease Control),
2,072 people have been diagnosed with West Nile virus in the United States in
year 2002 (until
today, Sep 26).
Illinois has had the most deaths, with 27. Louisiana and Michigan have had 11
each.
Among
those with severe illness due to West Nile virus, case-fatality rates range from
3% to 15%
and are highest among the elderly. However, less than 1% of those
infected with West Nile virus will develop severe illness. Currently no vaccine
is available, although the National Institute of Allergy and Infectious Diseases
(NIAID) has awarded a development grant for further research.
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What
types of mosquitoes
and birds carry West Nile virus?
Many mosquito species can become infected with
West Nile
virus. However, Culex pipiens
and Culex restuans
appear to have been the species most commonly infected during the
outbreaks in the U.S. in 1999, 2000 and 2001.
The number of bird
species in North America that play a role in the transmission of West Nile virus is not
known at this stage, although the virus has been identified in more than 70
species of birds in the USA during 1999, 2000 and 2001. High mortality rates
occur in some bird species, particularly crows, blue jays, gray jays, magpies
and ravens.
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What
are the symptoms?
Symptoms
are usually mild and include fever, headache, body aches, sometimes skin rash
and swollen lymph glands.
Encephalitis
symptoms ususally apperar between 5 to 15 days
after the bite from an infected
mosquito.
In the early stages, symptoms may include:
Anyone with those
symptoms should seek medical attention as soon as possible.
There is no
documented evidence that a pregnant woman or her fetus are at increased risk due
to infection with West Nile virus.
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Who
is most at risk
of contracting West Nile virus?
Anyone who is
exposed to mosquitoes in an area where West Nile virus has been detected has an
increased risk of infection. However, the risk of being bitten by a West Nile
virus-infected mosquito is low, as is the risk of serious health effects from
the virus for normally healthy people.
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Can you get West Nile virus from another person?
No. 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 disease, or from a health care worker who has treated someone with the
disease.
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How long does it take to get sick if bitten by an infected mosquito?
Being bitten by an infected mosquito will not necessarily make you
sick. Most people who are infected with West Nile virus have no symptoms or
experience only mild illness. If illness were to occur, it would occur within 3
to 15 days of being bitten by an infected mosquito.
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What
can you do to prevent it?
-
Minimize your time outdoors at dawn and
dusk when mosquitoes are most active and, whenever possible, wear long-sleeved
tops and long pants when spending time outside.
-
Use insect repellents, following safety
tips (Health Canada's information sheet Safety
Tips on Using Personal Insect Repellents). New York State
recommends the use of an insect repellant containing 10 per cent or less
DEET(N, N-diethyl-methyl-meta-toluamide) for children and no more than 30 per cent DEET
for adults.
-
Take action to
reduce mosquito breeding sites around your home, local parks and community.
-
Ensure that things in and around the
yard like pool covers, saucers under flower pots, children's toys, pet bowls and
wading pools are regularly emptied of standing water.
-
Clean eavestroughs of debris regularly
so water does not accumulate.
-
Empty and clean bird baths
regularly.
-
Ensure that openings in rain barrels are
covered with mosquito screening or tightly sealed around the down spout.
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Aerate ornamental ponds and stock with
fish that eat mosquito larvae.
-
Old tires are one of the most common
mosquito breeding sites. Ensure that your yard is free of debris, such as old
tires, that can accumulate rain water.
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What
proportion of people
with severe illness due to West Nile virus die?
Based on information from the US Centers for Disease Control and
Prevention (CDC), between 3% to 15% of people with serious health
effects due to West Nile virus die, and the proportion is highest amongst the elderly.
However, it is important to note that
<1% of those infected
with West Nile virus are reported to have developed severe health effects.
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How
does West Nile virus actually cause
serious health effects and death in humans?
After an individual is bitten by an
infected mosquito, West Nile virus multiplies in the person's blood system.
If the
virus crosses the blood-brain barrier to reach the brain, the virus will cause
inflammation of brain tissue and interfere with normal central nervous system
functioning.
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Is
there treatment for people infected with
West Nile virus?
There is no specific treatment, medication, or cure for West Nile virus.
However,
many of the symptoms and complications of the disease can be treated.
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Is
there a human vaccine?
There is no licensed human vaccine for West Nile virus at this time.
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Is
a woman's pregnancy
at risk if she gets West Nile virus?
There is no documented evidence that a pregnancy is at risk due to infection
with West Nile virus.
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If
West Nile virus activity
is reported near where I live and I'm bitten by a mosquito, am
I likely to get sick?
The chance of being bitten by an infected mosquito is
small. Even in areas
where mosquitoes carry the virus, very few mosquitoes - less than one per
cent - are likely to be infected.
Evidence suggests that
even if the mosquito is infected, less that one per cent of people who get
bitten and become infected will experience serious health effects.
However, as a
precaution it is still important to avoid exposure to mosquitoes in areas where
West Nile virus activity has been documented.
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What
if a mosquito bit
someone that had West Nile virus and then bit me? Would I become
infected?
There is no
documented evidence that mosquitoes have transmitted West Nile virus from one person to
another.
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I've been bitten by a mosquito. Should I be tested for West Nile virus?
No. Illnesses related to mosquito bites are still uncommon. However,
you should see a doctor immediately if you develop symptoms such as high fever,
confusion, muscle weakness, severe headaches, stiff neck, or if your eyes become
sensitive to light. Patients with mild symptoms should recover completely, and
do not require any specific medication or laboratory testing.
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How
do health care
providers test for West Nile virus?
Your Physician will first take a medical history to assess your risk
for West Nile virus. People who live in or have traveled to areas where West
Nile virus activity has been identified are at risk of getting West Nile
encephalitis; persons older than 50 years of age have the highest risk of
serious health effects.
If you are considered to be at high risk and have
symptoms of West Nile encephalitis, your physician will take a blood sample and
send it to a laboratory for testing.
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How
Is It Treated?
Once
diagnosed, patients with encephalitis may require hospitalization for close
monitoring as symptoms and complications can be serious. Treatment will be
determined based on a number of factors including age, condition and the form of
the disease. Treatment options may include antibiotics, fluids, fever and
pressure relief.
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If
a person is infected
with West Nile virus, does that person develop lifelong
immunity to future infection by the virus?
It is assumed that immunity will be lifelong; however, it may decrease in
later years.
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Am
I at Risk?
Even in areas where mosquitoes do carry the virus, very few mosquitoes-much less
than 1%-are infected. If the mosquito is infected, less than 1% of people who
get bitten and become infected will get severely ill. The chance you will become
severely ill from any one mosquito bite is extremely small.
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Is
West Nile virus (WNV) transmitted by blood transfusion or organ donation?
A recent investigation has identified transplanted organs as the source of WNV
infection in four recipients of organs from a single donor. How the organ donor
became infected is unknown. The organ donor might have become infected from a
mosquito bite or possibly acquired the infection through transfusion; an
investigation of the numerous transfusions received by the organ donor is
ongoing. Since the report of these cases, CDC has been informed of other
patients who developed WNV infection within several weeks of receiving blood
products or organs. Investigations are ongoing to determine whether WNV was
transmitted by transfusion or transplantation in any of these cases.
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Should
people avoid donating blood or getting blood transfusions or organ transplants?
A. Blood is lifesaving and is currently in short supply. Donating blood is safe,
and we encourage blood donation now and in the future. Approximately 4.5 million
persons receive blood or blood products annually. Although persons needing blood
transfusions or organ transplants should be aware of the risk for WNV infection,
the benefits of receiving needed transfusions or transplants outweigh the
potential risk for WNV infection.
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How can blood
banks avoid collecting blood from donors who may have West Nile virus?
A. On August 17, FDA issued an alert to blood banks and organizations to be
vigilant in excluding individuals who may have early symptoms of West Nile virus
from donating blood. Most people who have West Nile virus do not show symptoms,
making it difficult to defer them from donation. However, some individuals
develop minor symptoms of fever and headache. Blood banks need to be vigilant to
defer all of those who may have minor illnesses, especially in areas where West
Nile virus is most active.
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If a person
has had West Nile virus, can they still donate blood?
A. With West Nile virus infection, the viremia usually is transient, and people
clear the virus very quickly. Blood centers will take precautions (see preceding
question and answer) to be sure that donors who have been diagnosed with West
Nile virus have fully recovered before donating.
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If I recently
had a transfusion or transplant, should I be concerned about getting West Nile
virus?
A. You should be aware of the potential risk for WNV infection and the need to
monitor your health. If you have symptoms of West Nile virus or other concerns
you should contact your physician. However, it is important to remember that a
large number of WNV infections due to mosquito bites have occurred among persons
in the United States this year. By chance alone, some of these persons will have
received blood transfusions and/or organ transplantations. Recent receipt of a
blood transfusion or organ transplantation by a person with WNV infection does
not necessarily implicate the transfusion/transplantation as the source of
infection.
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What
role do commercial laboratories play in diagnosing people with
West Nile virus infection?
A.When
a person goes to see a health care provider, and has symptoms of a
West Nile illness a specimen may be sent to a commercial
laboratory to determine if the person has been infected by West
Nile virus. The tests used in commercial labs check for antibodies
to the virus (the body’s response to infection). The results of
the test will be sent to the doctor and the state health
department will be informed if the results are positive. There is
no specific treatment available for West Nile virus infection, so
the diagnosis will not necessarily change the way the person is
being treated but it will let the doctor know that he/she does not
have to investigate another cause of illness, and it will help the
health department know where the virus is active in order to focus
prevention measures.
The
state health department may choose to accept the positive results
from the commercial lab, or they may choose to test the sample
again in the state health department laboratory for confirmation
of the infection. The state health department will report the case
to CDC.
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How
accurate are the tests used in commercial labs?
The
tests used in commercial labs are modeled on the tests created by
CDC and used at CDC and in state public health laboratories. This
is the first year that many of these tests have been widely used
in commercial labs, and laboratories are learning more about the
specific measurements used in each test. Often, a second test will
be done to confirm the infection. State health departments, the
FDA (which licenses and regulates medical tools such as these
tests), the association of Public Health Laboratories and CDC are
all engaged in monitoring new commercial tests, and are committed
to working with industry to make these tests as accurate and
useful as possible.
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If
a test is a “false positive” what does that mean?
A
“false positive” occurs when an initial tests indicates that a
person does have a West Nile infection, but a later, more specific
tests indicates that the person does not actually have the
infection. While it is important to health department and CDC to
get an accurate idea of where people are being infected in order
to focus prevention and control efforts, the result does not have
a great impact on the individual person. There is no specific
treatment that the person would receive due to West Nile virus
infection. The person may want to work with their physician to see
if another cause of the illness needs to be identified.
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