LIVE POLIO IRUS VACCINES

Detection of a "Non-Detectable" Simian Virus
83
cell culture were found to be as high as 10-6.0
in 0.2 ml.
Only one of the 10 Cynomolgus cell-culture
lots revealed the vacuolating virus. However,
definitive tests of these lots for vacuolating virus
were not possible since eight of the lots were
heavily contaminated with what appeared to be
the foamy virus. Thus, vacuolating agent, if
present, may have been overgrown or excluded
by foamy virus.
Cultures of African green monkey-kidney prepared
in our laboratories have been found remarkably
free of the vacuolating agent. In the
course of use of more than 1000 lots of individual
monkey-cell cultures, presence of vacuolating
agent was suspect for only four lots and
proved for only one lot.
PROPERTIES OF THE VACUOLATING
VIRUS
Cytopathic eflect. Figures 1 and 2 show, respectively,
the outstanding changes caused by
vacuolating virus as observed in wet culture and
in stained preparations. Green monkey-kidney
cell cultures infected with about 1000 TCD,, of
vacuolating virus show beginning changes on day
3 or 4. At this time, some of the cells may appear
rounded or shrunken and may exhibit a
darkened cytoplasm. A few of the cells may
show beginning vacuolation of the cytoplasm.
With increased time, the typical changes develop.
These consist predominantly of enlargement
of cells which are spread out on the glass
or ballooning of free cells. The cytoplasm of
these cells becomes filled with vacuoles which
appear highly refractile in wet preparations and
which appear as "holes" with intensely stained
boundaries in stained preparations. The nucleus
may appear normal or disorganized internally.
Limited fusion of the cytoplasm of adjoining
cells may occur but, predominantly, each cell
maintains its own integrity. Thus, syncytia and
giant cells, such as occur with measles or foamy
virus infection, are not prominent in vacuolating
agent infection. Within 5 to 10 days, the
infected cells aggregate together and detach
from the glass leaving behind only small islands
of normal or degenerated cells.
No definitive cytoplasmic or nuclear inclusion
bodies have been observed to the present in H
and E stained preparations of cells infected
with the vacuolating virus. The cytopathic
changes caused by the vacuolating agent appear
quite distinct from those described for Hull's
four groups of simian viruses and for Malherbe's
and Harwin's seven simian agents.
Antigenic relationships. The strains of vacuolating
virus studied to date appear to comprise
a single immunologic group. As shown in Table
2, antisera against vacuolating agent strains 776
and 175 neutralized the homologous viruses and
all of three additional strains as well. Additionally,
all three strains of Sabin vaccine origin
were neutralized by strain 776 antiserum.
Strain 776 of vacuolating virus was not neutralized
by antiserum against group 4 SV-6,
SV-26, or SV-29 antisera furnished by Dr. Hull.
Additionally, it was not neutralized by Myxovirus
parainfluenza 1 or 3 antisera or by such
SA, SV-5 or foamy virus antisera as were im-
TABLE 2. ANTIGENIC RELATIONSHIPS OF SELECTED STRAINS OF VACUOLATING VIRUS AS MEASURED
IN SERUM NEUTRALIZATION TESTS
VIRUS STRAIN TESTED
TITER OF SERUM AGAINST STRAIN
776 175
776 4096 or > 800
175 4096 or > 1600
1095 4096 or > 2048
953 4096 or > 4096 or >
584 4096 or > 4096