[pct-l] How do people get infected with West Nile virus

[csx@xxxxxxxxxxxxxxxxxxx (Shawnie)]

How do people get infected with West Nile virus
http://www.cdc.gov/ncidod/dvbid/westnile/qa/transmission.htm
Transmission Updated

Q. How do people get infected with West Nile virus (WNV)?
A. The principle route of human infection with West Nile virus is through t=
he
bite of an infected mosquito. Mosquitoes become infected when they feed on
infected birds, which may circulate the virus in their blood for a few days=
. The
virus eventually finds its way into the mosquito's salivary glands. During
subsequent blood meals, the virus may be injected into humans and animals, =
where
it can multiply and possibly cause illness.

Additional routes of infection have become apparent during the 2002 West Ni=
le
epidemic. It is important to note that these other methods of transmission
represent a very small proportion of cases. A recent investigation has conf=
irmed
WNV transmission through transplanted organs. Investigations of other patie=
nts
who developed WNV infection within several weeks of receiving blood product=
s or
organs are ongoing to determine whether WNV was transmitted by transfusion =
or
transplantation in any of these cases.
There is one reported case of transplacental (mother-to-child) WNV transmis=
sion.
This case is detailed in MMWR Dec 20, 2002. Although transmission of WNV an=
d
similar viruses to laboratory workers is not a new phenomenon, two recent c=
ases
of WNV infection of laboratory workers have been reported. These cases are
detailed in MMWR Dec 20, 2002.


  View enlarged image.
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, t=
he
virus may be injected into the animal or human, where it may multiply, poss=
ibly
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 ar=
e
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 chance=
s 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 w=
ho
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 one documented case of transplacental (mother-to-child) transmi=
ssion
of WNV in humans. Although the newborn in this case was infected with WNV a=
t
birth and had severe medical problems, it is unknown whether the WNV infect=
ion
itself caused these problems or whether they were coincidental. More resear=
ch
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 f=
or
WNV and other arboviral infections by avoiding mosquitoes, using protective
clothing and repellents containing DEET (See Using Repellents Safely) 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 WN=
V
infection (see Symptoms) should undergo appropriate diagnostic testing.

For more details regarding the case described above, please see: MMWR Dec 2=
0,
2002.


Q. Can West Nile virus be transmitted through blood transfusions?
A. Please refer to Blood Transfusions and Transmission: Questions and Answe=
rs.

Q. Are laboratory workers in contact with WNV-positive specimens at risk fo=
r WNV
infection?
A. Yes, and approximately 20 laboratory-acquired WNV infections have been
reported in the medical literature over many decades. In the two most recen=
tly
reported cases, WNV infection of two microbiologists working with WNV-posit=
ive
samples resulted from percutaneous inoculation (pierced through the skin). =
Both
persons had mild, self-limited illnesses.

As more laboratories are have recently become involved in WNV diagnostic an=
d
reference activities, the risk for laboratory acquired WNV infections has
probably increased. Laboratory workers handling materials that are potentia=
lly
infected with WNV should use every precaution to minimize their risk for
exposure. For more details, please see: MMWR, Dec 20, 2002.


Q. Besides mosquitoes, can you get West Nile virus directly from other inse=
cts
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, the=
ir
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, squir=
rels,
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 th=
e
carcass in a garbage can.

Q. Can you get infected with West Nile virus by caring for an infected hors=
e?
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 follo=
wed
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 infecte=
d?
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 mammal=
s.

Q. How does West Nile virus actually cause severe illness and death in huma=
ns?
A. Following transmission by an infected mosquito, West Nile virus multipli=
es 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 a=
re
infected?
A. There is no scientific evidence indicating that people can be chronicall=
y
infected with West Nile virus. What remain in a person=92s body for long pe=
riods
of time are antibodies and =93memory=94 white blood cells (T-lymphocytes) t=
hat the
body produces to the virus. These antibodies and T-lymphocytes last for yea=
rs,
and may last for the rest of a person=92s life. Antibodies are what many
diagnostic tests look for when clinical laboratories testing is performed. =
Both
antibodies and =93memory=94 T-lymphocytes provide future protection from th=
e virus.

Q. If a person contracts West Nile virus, does that person develop a natura=
l
immunity to future infection by the virus?
A. It is assumed that immunity will be lifelong; however, it may wane in la=
ter
years.



--
"The degree to which we suffer indicates the degree to which we are alive.
When we take drugs to ease our suffering, we stifle our psychological and s=
piritual life."

 - Peter R. Breggin M.D.