274 STUDIES ON PASTEURELLA SEPTICA [Vol. XXVI, Part IV,
In many endemic areas, heavy mortality continues to occur in spite of two
inoculations carried out in a year and there are instances of even breakdown
in immunity soon after the vaccination. In such cases plurality of strains within
the species Past. septica was considered to be the probable cause. Investigations
were, therefore, taken up at the Indian Veterinary Research Institute with a view
to study the serological, biochemical and immunological differences in Past. septica
isolated from cases of the disease in different outbreaks and from different parts of
the country so as to select suitable strains for the preparation of haemorrhagic
septicaemia vaccines.
Serological studies: Rao [1953] typed serologically, by agglutination and agglu-
tin-absorption tests, 73 authentic strains of Past. septica. Forty-one strains included
in this study were isolated from cattle, i.e. 11 from buffaloes, one from a goat, 2 from
sheep, 3 from rabbits (N. C. T. C.), one from a cavy (N. C. T. C.), one from a cat, one
from a pig, nine from fowls, 2 from mice and one unclassified strain (N. C. T. C.).
The results of these tests confirmed the earlier observations of several workers such
as Jones [1921-22], Roderick [1922], Fitch and Nelson [1923], Lal [1927], Cornelius
[1929], Yusef [1935], Khalifa [1936], etc. that on serological grounds, the strains of
Past. septica cannot be classified according to the species of animals from which
they are isolated and also that there are several serological groups within the species.
In this study, 6 strains were found to correspond to Group I, 4 to Group II and 12
to Group IV of Cornelius. It was interesting to observe that 30 strains belonged to
one group serologically indistinguishable from the I. V. R. I. stock strain P 52.
However, the possibility of these strains belonging to Group III of Cornelius could
not be completely ruled out, as the Group III strain available with Rao might
not have been fully antigenic for absorption tests on account of its possible
change to 'R' type. The remaining strains did not fall into any of the groups tested.
On the basis of the above observations, Rao [1953] considered that the incorpo-
ration of strains representative of all the different antigenic groups was highly essen-
tial to overcome 'break-down' in the immunity produced by the present vaccines.
Biochemical studies: With a view to find out if the biochemical reactions would
follow the serological differences, Rao [1953] subjected all the 73 strains to biochemi-
cal studies but did not find characters that might be considered specific for any
serological grouping.
Immunological studies: Twenty seven authentic strains of Past. septica, 24 from
the cases of haemorrhagic septicaemia in bovines and three from the cases of fowl
cholera, were subjected to immunological studies by the mouse protection tests
on the lines of Roberts [1947] with a view to ascertain, if, like serological groups,
there also existed different immunological groups.
From these studies, it appeared that all the 24 strains from cases of haemorrhagic
septicaemia in bovines belonged to one immunological group, corresponding to type
I of Roberts while the three strains isolated from fowls belonged to a different
immunological group(s). The immunological studies are, however, being pursued
further with a larger number of strains collected from various parts of the country
and specific anti-sera are being produced using formalinised as well as heat-killed
antigens.