About West Nile
Virus
Transmission of West Nile Virus
Symptoms of West Nile Virus
Prevention of West Nile Virus
Testing and Treating West Nile Virus
in Humans
West
Nile Virus and Birds
West Nile Virus and Dogs and Cats
West Nile Virus and Horses
Map of Progression of West Nile Virus Across
the United States
What You Can do to Eliminate Mosquitoes
Transmission
of West Nile
Virus
Q. What is the basic
transmission cycle?
A. Mosquitoes become infected
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.
Q. If I live in an area where
birds or mosquitoes with West
Nile Virus
have
been reported and a mosquito bites me, and
I likely to get sick?
A. No. Even in areas where the
virus is circulating, very few mosquitoes
are infected with the virus. Even if the
mosquito is infected, less than one
percent of people who get bitten and
become infected will get severely ill. The
chances you will become severely ill from
any on mosquito bite are extremely small.
Q. Can you get West Nile
Encephalitis from another person?
A. No. West Nile Encephalitis 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.
Q. Is a woman's pregnancy at
risk if she gets West Nile Encephalitis?
A. There is one documented case
of trans-placental (mother-to-child)
transmission of WNV in humans. Although
the newborn in this case was infected with
WNV at birth and had severe medical
problems, it is unknown whether the WNV
infection itself caused these problems or
whether they were coincidental. More
research will be needed to improve our
understanding of the relationship-if
any-between WNV infection and adverse
birth outcomes.
Nevertheless, pregnant women should take
precautions to reduce their risk for WMV
and other arboviral infections by avoiding
mosquitoes, using protective clothing and
repellents containing DEET. When WNV
transmission is occurring in an area,
pregnant women who become ill should see
their health care provider. Those whose
illness is consistent with acute WNV
infection should undergo appropriate
diagnostic testing.
For more details regarding the case
described above, please see
Centers for Disease Control and Prevention
(CDC) MMWR Dec. 20, 2002.
Q. Is West Nile Virus (WNV)
transmitted by blood transfusion or organ
donation?
A. A recent investigation has
identified transplanted organs as the
source of WNV infection in four recipients
or 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 possible acquired
the infection through transfusion; an
investigation of the numerous transfusions
received by the organ donor is ongoing.
Since the report of these cases, the
Centers for Disease Control and Prevention
(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.
Q. Besides mosquitoes, can you
het West Nile Virus directly from other
insects or ticks?
A. Infected mosquitoes are the
primary source for West Nile Virus.
Although ticks infected with West Nile
Virus have been found in Asian and Africa,
their role in the transmission and
maintenance of the virus is uncertain.
However, there is no information to
suggest that ticks played any role in the
cases identified in the United States.
Q. How many types of animals
have been found to be infected with West
Nile Virus?
A. Although the vast majority of
infections have been identified in birds,
WNV has been shown to infect horses, cats,
bats, chipmunks, skunks, squirrels, and
domestic rabbits.
Q. How does West Nile Virus
actually cause severe illness and death in
humans?
A. Following transmission by an
infected mosquito, West Nile Virus
multiplies in the person's blood system
and crosses the blood-brain barrier to
reach the brain. The virus interferes with
normal central nervous system functioning
and causes inflammation of brain tissue.
Q. What proportion of people
with severe illness due to West Nile Virus
die?
A. Among those with severe
illness due to West Nile Virus,
case-fatality rates range from three
percent to 15% and are highest among the
elderly. Less than one percent of persons
infected with West Nile Virus will develop
severe illness.
Q. If a person contracts West
Nile Virus, does that person develop a
natural immunity to future infection by
the virus?
A. It is assumed that immunity
will be lifelong; however, it may wane in
later years.
(Information on this
page obtained from the Centers for Disease
Control and Prevention)
For West Nile Virus
information updates call toll free:
877-WNV-BIRD (877-968-273)
WestNile.ca.gov
Centers for Disease Control information on
West Nile Virus
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