LIVE POLIO IRUS VACCINES

Laboratory Investigations of Attenuated Poliovirus Vaccine Strains 93
confined to the lumbar cord whereas with the
other two strains lesions spread to the cervical
cord and brainstem.
Table 3 shows the results with the Type 2
strains. Here, the results are quite different
from those produced with the Type 1 strain.
No animals became paralyzed and indeed only
occasional animals showed histologic evidence
of poliomyelitis. Certainly, none of the Type 2
strains appear to have much neurovirulence
when inoculated intramuscularly. Table 4 shows
the results with the Type 3 strains and again
none of the strains appear to have much virulence.
In general, the lesions seen in the paralyzed
animals were as severe as those previously described
after direct inoculation into the CNS.
In some of the non-paralyzed animals, extensive
lesions were also seen. In many of these, the
lesions were only present in a single level, either
lumbar or cervical. It is of interest to note
that, in one monkey, at least, localized lesions
of poliomyelitis were present in the lumbar
spinal cord after inoculation of the vaccine into
the upper arm muscles.
How does invasion of the CNS occur after
intramuscular inoculation? Two possible routes
are: spread along peripheral nerves, or viremia,
leading to invasion of the CNS.
Investigations were undertaken to answer this
question. The Type 1 strains were chosen for
initial study since these appeared to exhibit the
highest degree of neurovirulence. Monkeys that
had been inoculated with Lederle and Sabin
strains intramuscularly and intravenously, were
bled on days 1, 2, 3, 5, 7, and 9. Viremia oc-
TABLE 4.
NEUROVIRULENCE
FOLLOWING INTRAMUSCULAR INOCULATION
TYPE 3 ATTENUATED POLIOVIRUS
OF RHESUS MONKEYS WITH
Inoculum-P. F. U.
Histopathology
Clinical Lumbar 1 Cervical B.S.
Signs
Koprowski Type III
1084_108. 6 -
107.7-108.1 1/4* 2/4 1/4 1/4
106.9-107.1 0/4 0/4 0/4 0/4
Lederle Type III
.4-14806 -.
107.7-108.1 0/4 1/4 0/4 0/4
106.9-107.1 0/6 1/6 0/6 0/6
Sabin type III
108.4-108.6 0/4 0/4 0/4 0/4
107. 7 -_10 8 1 0/6 0/6 0/6 0/6
106.9-107.1 0/4 0/4 0/4 0/4
*No. of monkeys having findings/No. inoculated.