LIVE POLIO IRUS VACCINES

20. LIVE VIRUS VACCINE STUDIES IN SOUTHERN AFRICA
JAMES H. S. GEAR
Poliomyelitis Research Foundation
South African Institute for Medical Research
Johannesburg, Union of South Africa
DR. GEAR (presenting the paper):
EARLY STUDIES
Work on the development of a live virus vaccine
against poliomyelitis began at the South
African Institute for Medical Research in 1946,
when an attempt to attenuate the Lansing strain
of the virus by passage in Mystromys albicaudatus,
a veld rodent, was initiated. At the beginning,
the virus paralyzed nine of 10 monkeys,
Cercopithecus aethiops pygerythrus, inoculated
intracerebrally, two of seven after 47 passages,
and after 100 passages, and again after 150 passages,
only one of the 10 monkeys inoculated
intracerebrally developed paralysis, indicating
that some attenuation of the virus for these
monkeys had occurred. A feeding trial was contemplated
at this stage and arrangements were
actually made, but not carried out.
At about the 180th passage, the virus suddenly
increased greatly in virulence for the rodents and
most of them developed paralysis within 24 hours
of inoculation. It was suspected that some other
virus such as EMC or Columbia SK had been
picked up in the course of passage, but identity
tests showed that the virus was still a Type 2
poliovirus. This finding might be of some interest
to those who, some years ago, were interested
in low titer and high titer Lansing virus. It
was found that its virulence for monkeys had also
increased again, and six of the 10 vervet monkeys
inoculated intracerebrally developed paralysis.
It was also found to be relatively non-cytopathogenic
in tissue cultures.
At this time, the whole energies of the staff of
the institution had to be devoted to the preliminary
studies and then to the production of a
formalin-inactivated vaccine. Work on the attenuation
of the virus was discontinued.
474
IMMUNITY SURVEYS
Immunity surveys, as part of a study of the
epidemiology of poliomyelitis in this region and
also to assess the need of various groups for protection,
have been carried out on representative
samples of the populations of the Territories of
Southern Africa and of the neighboring islands
in the Atlantic and Indian Oceans.
These have shown, in general, that most children
of the indigenous African native population
have developed antibodies against all three types
of poliovirus by the time they are six years old.
On the other hand, in those of European descent,
most of whom live under good conditions of
hygiene, there is a lower degree of immunity and
some adults lack immunity to all three types of
virus, a larger number to two, and a still larger
number to one type of poliovirus.
The incidence of the paralytic disease in the
past has been in keeping with these serological
findings. In the African native population, nearly
all cases occur in children under six years old,
and most of the cases in infants under three years
old. However, within the last five years, the condition,
previously sporadic, has begun to occur in
epidemics of increasing severity. The fact that
a large proportion of the population in the large
urban centers, for example about 70 per cent in
Johannesburg, has been rehoused in model townships
provided with waterborne sewerage, may be
partly responsible for the increasing incidence.
In the population of European descent most cases
still occur in children under 10 years old, but
there is a wider spread of incidence. Cases are
frequent in older children and adolescents and
not uncommon in adults, in whom the illness
tends to be severe and often fatal.