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West
Nile Virus: Q & A
Who's at Risk?
Q. Who is at risk for getting West Nile encephalitis?
A. All residents of areas where virus
activity has been identified are at risk of getting West Nile encephalitis;
persons over 50 years of age have the highest risk of severe disease. There is
no clear link between the level of a person's overall health and their risk of
getting severe disease. For example, it is unknown if immunocompromised persons
are a higher risk for the severe types of West Nile virus-related disease. This
topic is under investigation by CDC scientists.
Symptoms
Q. What are the symptoms of West Nile virus infection?
A. Most people who are infected with West
Nile virus will not have any type of illness. It is estimated that 20% of the
people who become infected will develop West Nile fever: mild symptoms,
including fever, headache, and body aches, occasionally with a skin rash on the
trunk of the body and swollen lymph glands.
The symptoms of severe infection (West Nile encephalitis, meningitis, and
meningoencephalitis) include headache, high fever, neck stiffness, stupor,
disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. It
is estimated that 1 in 150 persons infected with West Nile virus will develop a
more severe form of disease.
Q. What is the incubation period in humans (i.e., time from infection to
onset of disease symptoms) for West Nile encephalitis?
A. Usually 3 to 14 days.
Q. How long do symptoms last?
A. Symptoms of mild disease will generally last a few days. Symptoms of
severe disease may last several weeks, although neurological effects may be
permanent.
Q. I think I have symptoms of West Nile virus infection. What should I do?
A. Contact your health care provider if you have concerns about your health.
If you or your family members develop symptoms such as high fever, confusion,
muscle weakness, and severe headaches, you should see your doctor immediately.
Transmission
Q. How do people get
infected with West Nile virus?
A. People become infected by the bite of a mosquito infected with West
Nile virus.
Q. What is the basic
transmission cycle of West Nile virus?
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, am 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 1% of
people who get bitten and become infected will get severely ill. The chances you
will become severely ill from any one 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 infected with West Nile virus?
A. There is no documented evidence that a pregnancy is at risk due to
infection with West Nile virus.
Q. Can you transmit
West Nile virus through blood transfusions?
A. Please refer to Blood
Transfusions and Transmission below.
Q. Besides mosquitoes,
can you get 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 Asia 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, WN virus has been shown to infect horses, cats, bats, chipmunks, skunks,
squirrels, and domestic rabbits.
Q. Can you get West
Nile virus directly from birds?
A. 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 and use gloves or double plastic bags to place
the carcass in a garbage can.
Q. Can you get
infected with West Nile virus by caring for an infected horse?
A. West Nile virus is transmitted by infectious mosquitoes. There is no
documented evidence of person-to-person or animal-to-person transmission of West
Nile virus. Normal veterinary infection control precautions should be followed
when caring for a horse suspected to have this or any viral infection.
Q. Can you get WNV
from eating game birds or animals that have been infected?
A. There is no evidence that WNV virus can be transmitted to humans
through consuming infected birds or animals. In keeping with overall public
health practice, and due to the risk of known food-borne pathogens, people
should always follow procedures for fully cooking meat from either birds or
mammals.
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. How long does the
West Nile virus remain in a person’s body after they are infected?
A. There is no scientific evidence indicating that people can be
chronically infected with West Nile virus. What remain in a person’s body for
long periods of time are antibodies and “memory” white blood cells
(T-lymphocytes) that the body produces to the virus. These antibodies and
T-lymphocytes last for years, and may last for the rest of a person’s life.
Antibodies are what many diagnostic tests look for when clinical laboratories
testing is performed. Both antibodies and “memory” T-lymphocytes provide
future protection from the virus.
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.
Updated
Blood
Transfusions and Transmission
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 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.
Q. What is being done about the possibility of transfusion-related WNV
transmission?
A. CDC, FDA, blood collection agencies, and state and local health departments
are investigating possible cases of WNV transmission through blood transfusion
and organ transplantation. For cases currently under investigation, any
remaining blood products from donors whose blood was transfused to patients
with confirmed or suspected WNV infection have been withdrawn and efforts are
underway to contact these donors as well as other recipients of blood products
from these donors for follow up.
As part of the investigation, CDC has asked that physicians notify public
health authorities of any patients who develop symptoms of WNV infection
within 4 weeks of receiving a blood transfusion or organ transplantation. In
addition, patients with WNV infection whose symptoms begin in the weeks
preceding blood or organ donation should also be reported. Prompt reporting of
these persons will help facilitate withdrawal of potentially infected blood
components.
Q. 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.
Q. 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.
Q. 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.
Q. 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.
New West
Nile Virus and Breast-feeding
Q. Can West Nile virus be
transmitted through breast milk?
A. Based on a recent case in Michigan, it appears that West
Nile virus can be transmitted through breast milk. A new mother in Michigan
contracted West Nile virus from a blood transfusion shortly after giving
birth. Laboratory analysis showed evidence of West Nile virus in her breast
milk. She breastfed her infant, and three weeks later, her baby's blood tested
positive for West Nile virus. Because of the infant's minimal outdoor
exposure, it is unlikely that infection was acquired from a mosquito. The
infant was most likely infected through breast milk. The child is healthy, and
does not have symptoms of West Nile virus.
Q. Should I continue breast-feeding if I am symptomatic for West Nile
virus?
A. Because the health benefits of breast-feeding are well
established, and the risk for West Nile virus transmission through
breast-feeding is unknown, the new findings do not suggest a change in
breast-feeding recommendations. The American Academy of Pediatricians and the
American Academy of Family Physicians recommend that infants be breastfed for
a full year of life.
Lactating women who are ill or who are having difficulty breast-feeding for
any reason, as always, should consult their physicians.
Q. Should I continue breast-feeding if I am not symptomatic for West Nile
virus?
A. Yes. Because the health benefits of breast-feeding are
well established, and the risk for West Nile virus transmission through
breast-feeding is unknown, the new findings do not suggest a change in
breast-feeding recommendations.
Q. If I am breast-feeding, should I be tested for West Nile virus?
A. No. There is no need to be tested just because you are
breast-feeding.
Q. Is there any evidence that West Nile virus is transmitted from mother to
child during pregnancy or during birth?
A. There is no evidence that West Nile virus can be
transmitted during pregnancy or birth.
Q. Are infants at higher risk than other groups for illness with West Nile
virus?
A. No. West Nile virus illnesses in children younger than
1-year-old are infrequent. During 1999-2001, no cases in children younger than
one year of age were reported to CDC. Of the over 2500 total West Nile Virus
cases in 2002, only four were less than one year of age. We know that one of
these infants was not breast-feeding, and investigation of the other infants
is underway.
Q. If I am breast-feeding, should I use insect repellent containing DEET?
A. Yes. Insect repellents help people reduce their exposure
to mosquito bites that may carry potentially serious viruses such as West Nile
virus, and allow them to continue to play and work outdoors. There are no
reported adverse events following use of repellents containing DEET in
pregnant or breast-feeding women.
Testing and Treatment
Q. How do health care providers test for West Nile virus infection?
A. Your physician will first take a
medical history to assess your risk for West Nile virus. People who live
in or traveled to areas where West Nile virus activity has been identified
are at risk of getting West Nile virus-related disease; persons older than
50 years of age have the highest risk of severe disease. If you are
determined to be at high risk and have symptoms of West Nile encephalitis,
your provider will draw a blood sample and send it to a commercial or
public health laboratory for confirmation.
Q. How is West Nile virus-related disease treated?
A. There is no specific treatment for West Nile virus-related
diseases. In more severe cases, intensive supportive therapy is indicated,
often involving hospitalization, intravenous fluids, airway management,
respiratory support (ventilator), prevention of secondary infections
(pneumonia, urinary tract, etc.), and good nursing care.
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