LIVE POLIO IRUS VACCINES

6. DETECTION OF A "NON-DETECTABLE" SIMIAN VIRUS
(VACUOLATING AGENT) PRESENT IN RHESUS AND CYNOMOLGUS
MONKEY-KIDNEY CELL CULTURE MATERIAL.
A PRELIMINARY REPORT
B. H. SWEET AND M. R. HILLEMAN
Division of Virus and Tissue Culture Research,
Merck Institute for Therapeutic Research,
West Point, Pennsylvania
DR. HILLEMAN (presenting the paper): A
number of viral agents have been recovered
from the tissues and excreta of monkeys. 1-6 Certain
of these agents are present in high frequency
in kidney-cell cultures of these animals.
These agents are currently called simian or
ECMO viruses. Hull 3 has classified the simian
viruses into four groups (CPE groups 1, 2, 3,
and 4) based on the kind of cytopathic change
induced in monkey-kidney cell cultures infected
with these agents. Twenty-eight of these viruses
were precisely separated serologically into types
and, additionally, 24 "unidentifiable" viruses
were recorded. Malherbe and Harwin4 distinguished
seven distinct types among the SA viruses
they recovered from vervet monkey materials.
The simian viruses of monkey kidney origin
present a real problem in the virus application
of the cell culture technique. Thus, indigenous
simian virus may contaminate or even exclude
the inoculated virus on passage in monkeykidney
cell culture. Virus-infected culture fluids
used to prepare killed poliomyelitis or adenovirus
vaccine are commonly contaminated with
simian agents and assurance must be provided
for the inactivation of both the intended and
the simian viruses in these vaccines. Testing for
such "intruding" viruses may be further complicated
by the presence of such agents in the cultures
used to perform the tests. Finally, such
simian viruses must be definitively excluded
from any live virus vaccine intended for routine
use in man since the long-term effect of
human infection with these agents is unknown
and since data on short-term effect are either
meager or entirely lacking.
All of the presently reported simian viruses derived
from monkey-kidney cell culture have been
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detected in kidney-cell cultures of the same monkey
species, either in the primary culture itself
or on further passage. Thus, all of the agents
previously reported have been readily detectable
and can be excluded on the basis of rigid testing
in monkey cell cultures. The question has often
been raised concerning hypothetical "non-detectable"
simian viruses, i.e., those agents which
might be present in monkey kidneys but which
cannot be detected by current procedures.
During the past two years, our virus research
work has repeatedly uncovered what appears to
be a new simian virus of Rhesus and Cynomolgus
monkey kidney origin and which does not cause
significant cytopathic change in kidney-cell cultures
of these same species. The agent does,
however, cause very marked and distinetive cytopathic
changes in kidney-cell cultures of the
African green monkey, Cercopithecus aethiops
[grivet, according to Sanderson ], obtained
from equatorial East Africa. In our laboratory,
we have referred to this virus as the "vacuolating
agent", because of the prominent cytoplasmic
vacuolation seen in infected cell cultures.
Dr. Hull has suggested that this vacuolating
virus be designated S.V. 40 and be included in
Hull's C.P.E. Group 4.3
Studies in our laboratory of the vacuolating
agent have been directed mainly toward its
elimination rather than its emulation. Hence,
certain aspects of the work are scanty or still
in progress. The present report, which is preliminary,
records the findings to date.
ORIGIN OF STRAINS OF VACUOLATING
VIRUS
Vacuolating virus is readily recovered from
contaminated virus seed stocks by passage of
the virus seed, in the presence of its homologous