Webster's New World Medical Dictionary

particles enter the blood and go to other sites,
where the virus multiplies more extensively. Another
round of virus in the bloodstream leads to invasion
of the spinal cord and brain, the target sites struck
by the virus. When the central nervous system (CNS)
is inflamed, the anterior horn cells of the spinal
cord and the brainstem are especially affected.
Polio is a minor illness in 80 to 90 percent of clini-
cal infections; this is termed the abortive type of
polio. Abortive polio appears chiefly in young chil-
dren and does not involve the CNS. Symptoms are
slight fever, malaise, headache, sore throat, and
vomiting 3 to 5 days after exposure. Recovery
occurs in 24 to 72 hours. As a major illness, polio
may or may not cause paralysis. Symptoms usually
appear without prior illness, particularly in older
children and adults, 7 to 14 days after exposure.
Symptoms are fever, severe headache, stiff neck and
back, deep muscle pain, and sometimes areas of
increased or altered sensation. There may be no
further progression from this type of illness, which
is similar to viral meningitis, or there may be loss of
tendon reflexes and weakness or paralysis of mus-
cle groups. Recovery is complete with the abortive
and nonparalytic forms of polio, although a set of
symptoms known as postpolio syndrome may
appear many years later. In paralytic polio, about 50
percent of patients recover, with no residual paraly-
sis; about 25 percent are left with mild disabilities,
and the remaining 25 percent of patients have
severe permanent disability. The ideal strategy
with polio is clearly to prevent it by immunizing
against poliovirus. Also known as infantile paralysis
and poliomyelitis. See also 
postpolio syndrome.
polio, abortive
A minor form of infection with
poliovirus that accounts for 80 to 90 percent of clin-
ically apparent cases of polio in the US, chiefly in
young children. The usual symptoms—slight fever,
malaise, headache, sore throat, and vomiting—
emerge 3 to 5 days after exposure to the virus. Full
recovery occurs in 24 to 72 hours. Abortive polio
does not involve the nervous system or cause per-
manent disabilities of any kind.