LIVE POLIO IRUS VACCINES

Application of Genetic Markers to Development and Control of Vaccine 59
TABLE 9. STUDY OF PATHOGENICITY FOR RHESUS MONKEYS INJECTED INTRASPINALLY WITH TYPE 1
VIRUS (W-1 STRAIN) AT VARIOUS PASSAGE LEVELS AT LOW
TEMPERATURES
TEMPERATURE PASSAGE TCD 5 0 RATIO OF MONKEYS SHOWING LSSIONS
OF TISSUE CULTURE INJ. L C B.S.
250 C 10 7.2 5/5 4/5 2/5
230 C 10 + 5 6.2 3/4 3/4 3/4
10 + 5
PLAQUED* 6.7 1/4 1/4 0/4
* At 23 ° C.
was examined for histopathologic lesions after
they were sacrificed 18-20 days after inoculation.
It will be observed that the results obtained with
the W-1 strain after 10 passages at 250 C., followed
by five passages at 230 C., did not seem
to distinguish this strain from other attenuated
strains. Progeny of a plaque isolated after 15
passages at low temperature (23 ° C.) have
proved remarkably less neurovirulent than other
available attenuated strains.
The original W-1 virus and the plaqued cold
variant were submitted to the intratypic serodifferentiation
test using serum overlay prepared
against the original strain. Results of this test,
shown on Table 10, indicate serologic identity of
the plaqued cold variant with the original virus.
The TN Type 2 strain-the first strain ever to
be fed to a human being-was chosen to initiate
passages of Type 2 strains at low temperatures.
Two Type 3 strains were employed to initiate a
series of passages at low temperatures. One was
isolated by Gelfand and Fox from the feces of
an asymptomatic child in Louisiana (W-3), and
the other represents the first human passage of
the Fox Type 3 strain which retained the cold
character of the original virus. Following serial
passages at low temperatures and change in the
temperature and MS markers of the strains
similar to those observed with the W-1 virus,
neuropathogenicity tests were carried out in in-
TABLE 10. INTRATYPIC SERODIFFERENTIATION TEST BETWEEN THE W-1 ORIGINAL VIRUS AND ITS
"COLD"
VARIANT
PASSAGE
AT 23-250°C
AVERAGE NUMBER OF PLAQUES
CONTROL OVERLAY
ANTI-W-I SERUM* OVERLAY
0 14 3
8 6