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.
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.
Milder Symptoms in Some People. Up to 20 percent of the
people who become infected will display symptoms which
can include fever, headache, and body aches, nausea,
vomiting, and sometimes swollen lymph glands or a skin
rash on the chest, stomach and back. Symptoms can last
for as short as a few days, though even healthy people
have been sick for several weeks.
No Symptoms in Most People. Approximately 80 percent of
people (about 4 out of 5) who are infected with WNV will
not show any symptoms at all.
How Does West Nile Virus Spread?
Infected Mosquitoes. Most often, 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 been 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.
What Is the Risk of Getting Sick
from WNV?
People over 50 at higher risk to get sick. 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.
Being outside means you're at risk. The more time you're
outdoors, the more time you could be bitten by an
infected mosquito. Pay attention to avoiding mosquito
bites if you spend a lot of time outside, either working
or playing.
Risk through medical procedures is very low. All donated
blood is checked for WNV before being used. The risk of
getting WNV through blood transfusions and organ
transplants is very small. If you have concerns, always
consult your doctor.