West Nile Virus
What is it?
West Nile virus is a type of arbovirus, which
is short for arthropod-borne virus. The virus that
causes West Nile virus is carried by mosquitoes,
and is transmitted to animals and humans through
their bite. An organism that carries a disease,
without actually developing the disease, is called
a vector. West Nile virus is also called West Nile
encephalitis. Encephalitis is an infection of the
brain. Who gets it?
West Nile virus is primarily seen in horses and
birds, but has more recently affected humans. West
Nile virus has been described in Africa, Europe,
the Middle East, west and central Asia, Oceania,
and in 1999, North America. Since 1999, the
Centers for Disease Control (CDC) has reported 149
cases of severe West Nile virus, including 18
deaths, in the United States. However, fewer than
one percent of all mosquitoes are infected with
West Nile. So, the chances of becoming severely
ill from a mosquito bite is small. People over the
age of 50 are at the highest risk for developing
severe symptoms. What causes it?
Mosquitoes become infected with West Nile Virus
when they bite infected birds. The virus is
located in the mosquito's salivary glands. When a
mosquito that is carrying West Nile virus bites an
animal or person, the virus (called Flavivirus
Japanese Encephalitis Antigenic Complex),
multiplies in the person's blood system before
crossing the blood-brain barrier to reach the
brain. Once in the brain, the virus causes the
brain tissue to become inflamed, which in turn
interferes with normal central nervous system
functioning. West Nile virus is not contagious,
which means one person cannot pass it directly to
another. There is also no evidence that people can
get West Nile virus from handling infected birds
or other animals. However, if you find a dead
bird, you should wear gloves or use some other
type of protective barrier when handling the dead
animal. What are the symptoms?
Symptoms occur around 3 to 15 days after being
bitten by an infected mosquito. West Nile virus
usually causes a mild infection with flu-like
symptoms that include fever, headache, and body
aches. Some people may also develop a skin rash
and swollen lymph glands. In more severe cases,
the patient develops meningoencephalitis, which is
an inflammation of the spinal cord and brain.
Symptoms can include severe headache, high fever,
stiff neck, stupor, disorientation, coma, tremors,
convulsions, muscle weakness, and paralysis. West
Nile virus results in death in approximately 3 to
15 percent of all cases, primarily among the
elderly. It appears that those who develop West
Nile virus are then immune to any future West Nile
infections. How is it diagnosed?
Your doctor will take a complete medical
history so he or she can assess your risk factors
for West Nile virus. He or she will also perform a
complete physical examination. If your doctor
thinks you may have West Nile virus, he or she
will take a blood sample to be tested for the
virus in a laboratory. What is the treatment?
West Nile virus, like other arbovirus
infections, must run its course. Treatment is
focused on medications to lower fever and reduce
pain, fluids to prevent dehydration, and bed rest.
In severe cases, patients may need to be
hospitalized, where they are treated with
intravenous fluids and oxygen therapy, as well as
monitored for secondary infections such as
pneumonia. The majority of patients with West Nile
virus make a complete recovery. Self-care tips
You can protect yourself from mosquito bites by
using a mosquito repellent spray or lotion on your
body and clothes and staying in well-screened
areas. Wear long-sleeved shirts and pants when
outdoors. If you are traveling to a country that
is known to have a high population of West
Nile-carrying mosquitoes, your sleeping area
should have mosquito netting over the bed. Avoid
leaving any containers of standing water outside
where mosquitoes can breed. See a healthcare
professional immediately if you have been in an
area where West Nile virus is common and you have
any illness with symptoms such as high fever,
severe headache, confusion, and muscle weakness.
This information has been designed as a comprehensive and quick reference
guide written by our health care reviewers. The health information written
by our authors is intended to be a supplement to the care provided by your
physician. It is not intended nor implied to be a substitute for
professional medical advice.
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