What is the “acute flaccid paralysis” that sometimes
occurs with WNV infection?
A. In addition to West Nile fever, meningitis, or encephalitis,
some people who become infected with WNV can develop “acute
flaccid paralysis”—a sudden onset of weakness in
the limbs and/or breathing muscles. In most persons, acute flaccid
paralysis is due to the development of West Nile poliomyelitis—an
inflammation of the spinal cord that causes a syndrome similar
to that caused by the poliovirus. West Nile poliomyelitis was
first widely recognized in the United States in 2002. Persons
with West Nile poliomyelitis may develop sudden or rapidly progressing
weakness. The weakness tends to affect one side of the body more
than the other, and may involve only one limb. The weakness is
generally not associated with any numbness or loss of sensation,
but may be associated with severe pain. In very severe cases,
the nerves going to the muscles that control breathing may be
affected, resulting in rapid onset of respiratory failure. It
is important to recognize that this weakness may occur in the
absence of meningitis, encephalitis, or even fever or headache—there
may be few other clues that the weakness is due to WNV infection.
How often does West Nile poliomyelitis occur?
don’t know for sure how often West Nile poliomyelitis
occurs, but it does occur less frequently than meningitis
or encephalitis. Scientists are continuing to monitor persons
with West Nile poliomyelitis to get a better understanding
of how often, and in whom, it occurs.
Are there other types of weakness or “acute
flaccid paralysis” caused by WNV infection?
A. The vast majority of persons with WNV “acute flaccid
paralysis” suffer from West Nile poliomyelitis
(an inflammation of the spinal cord). Some persons
with WNV infection may instead develop an illness
similar to Guillain-Barré syndrome, which
is a disease of the peripheral nerves and not the
spinal cord. Weakness of the facial muscles may also
develop in persons with WNV infection. While many
persons with WNV infection experience fatigue and
feel weak all over, this is not the same as “acute
Who tends to be affected by West Nile poliomyelitis?
A. People of
any age can be affected by West Nile poliomyelitis. While persons
over the age of 65 are at highest risk for all forms
of WNV neuroinvasive disease, including poliomyelitis, persons
of younger age groups (e.g., in their 30’s and 40’s)
can also develop West Nile poliomyelitis. West Nile poliomyelitis
may affect people who are otherwise healthy and without prior medical
What is the likelihood that people who experience weakness due
to West Nile poliomyelitis will recover?
is not yet clear the extent to which people who develop weakness
due to West Nile poliomyelitis will recover. Some people do recover
completely, others recover partially, and there are still others
who have not shown significant recovery in over one year. Researchers
continue to monitor patients who have been affected in order to
better understand the long-term outcome of West Nile poliomyelitis
and to determine whether there are any treatments that are beneficial.