What Is West Nile Virus?
West Nile virus (WNV) is a potentially serious illness. Experts believe WNV is established
as a seasonal epidemic in North America that flares up in the summer and continues
into the fall. This fact sheet contains important information that can help you
recognize and prevent West Nile virus.
What Are the Symptoms of WNV?
WNV affects the central nervous system. Symptoms vary.
- No Symptoms in Most People. Approximately 80 percent of people who are infected
with WNV will not show any symptoms at all.
- Mild Symptoms in Some People. Up to 20 percent of the people who become infected
will display mild symptoms, including fever, headache, and body aches, nausea, vomiting,
and sometimes swollen lymph glands or a skin rash on the chest, stomach and back.
Symptoms typically last a few days.
- Serious Symptoms in a Few People. About one in 150 people infected with WNV
will develop severe illness. The severe symptoms can include high fever, headache,
neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness,
vision loss, numbness and paralysis. These symptoms may last several weeks, and
neurological effects may be permanent.
How Does It Spread?
Infected Mosquitoes. Generally, WNV is spread by the bite of an infected mosquito.
Mosquitoes are WNV carriers that become infected when they feed on infected birds.
Infected mosquitoes can then spread WNV to humans and other animals when they bite.
- Transfusions, Transplants, and Mother-to-Child. In a very small number of
cases, WNV also has spread through blood transfusions, organ transplants, breastfeeding
and even during pregnancy from mother to baby.
- Not through touching. WNV is not spread through casual contact such as touching
or kissing a person with the virus.
How Soon Do Infected People Get Sick?
People typically develop symptoms between 3 and 14 days after they are bitten by
the infected mosquito.
How Is WNV Infection Treated?
There is no specific treatment for WNV infection. In cases with mild symptoms, people
experience symptoms such as fever and aches that pass on their own. In more severe
cases, people usually need to go to the hospital where they can receive supportive
treatment including intravenous fluids, help with breathing and nursing care.
What Should I Do if I Think I Have WNV?
Mild WNV illness often improves on its own, and people do not necessarily need to
seek medical attention for this infection, however it is always best to check with
your physician, if uncertain. If you develop symptoms of severe WNV illness, such
as unusually severe headaches or confusion, seek medical attention immediately.
Severe WNV illness usually requires hospitalization. Pregnant women and nursing
mothers are encouraged to talk to their doctor if they develop symptoms that could
What Is the Risk of Catching WNV?
For most, risk is low. Less than 1 percent of people who are bitten by mosquitoes
develop any symptoms of the disease and relatively few mosquitoes actually carry
WNV. People over the age of 50 are more likely to develop serious symptoms of WNV
if they do get sick and should take special care to avoid mosquito bites.
For More information on WNV:
Centers for Disease Control - West Nile Virus Home Page