STUDIES ON SALMONELLA ABORTUS EQUI VACCINE
By M. R. DHANDA, J. M. LALL and M. M. SINGH Pathology and Bacteriology
Division, Indian Veterinary Research Institute, Mukteswar-Kumaun
(Received for publication on 16th February 1954)
O STERTAG [1901] described a gram-negative streptococcus as the specific
organism responsible for infectious abortions in mares, but the finding was
not confirmed for a number of years. Later researches by de Jong [1912], Van
Heelsbergen [1913], Lautenbach [1913], Meyer and Boerner [1913], however,
led to the conclusion that a bacterium of the paratyphoid group was generally the
cause of abortion in mares; and a large volume of literature has subsequently accu-
mulated to show the importance of Salmonella abortus equi in causing huge economic
loss in countries where horse breeding is done. The disease got a very firm foot-
hold during and after the World War I especially in Germany, France and Japan
owing to deficiency in the feeding and care of animals and frequent intermingling
of positive cases with healthy ones. India had also been badly affected by it and,
therefore, studies on the disease with the aim of formulating control measures and
evolving a suitable vaccine, were started at the Indian Veterinary Research Insti-
tute as far back as 1920, and it was after 10 years of extensive investigation that in
1930 it became possible to produce a satisfactory prophylactic vaccine against it.
The vaccine, as it was prepared in 1930, consisted of an emulsion of one part
of each of the 12 strains of B. abortivo-equinus and two parts of a strain of 'Mare
abortion coli' in 0.5 per cent carbolic acid in normal saline solution, brought to S.O.
60 and killed at 65°C for three hours. After five years of trial with this bacterin
the 'mare abortion coli' was eliminated and only three strains of Salmonella abortus
equi were incorporated and the opacity of the vaccine was reduced to S. O. 50. In
1946, all the previous cultures were substituted by three freshly isolated Coleyana
strains. These organisms, after being grown upon agar in Roux flasks and incu-
bated at 37°C for 24 hours, were emulsified in 0.5 per cent carbolic acid in normal
saline solution and diluted with the same suspending fluid to an opacity equal to
B.W. 4. This suspension was then killed in a water-bath at 56°C for ½ hour. The
vaccine was issued to the field till 1949 when it was found that following its inocu-
lation sometimes symptoms resembling those observed in toxaemic conditions
developed. The symptoms were more marked in the previously unvaccinated
animals receiving the vaccine for the first time while those that had been injected
with it previously hardly showed any untoward effect. The important symptoms
observed were dysponea, shivering, frequent attempts at micturition, defaction,
colicy pains, etc. which generally developed in about 20-40 minutes after injec-
tion of the vaccine and passed off in a few hours. On close scrutiny of records of the
past 19 years or so, no history of such symptoms having been observed could be
traced. However, the temperature charts always showed a rise of 1° to 4°F follow-
ing vaccination and a fairly pronounced swelling at the site of inoculation which
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