28
VOLE
VACCNATION
[Vol. XXIII, Part I,
There are two facts about the above experiment to which attention might be
drawn in trying to explain the discrepant results obtained by Sahai and those obtained
by other workers in guinea-pigs. The first of these relates to the virulence of the
strain used in these experiments. This strain, LV 285, had been isolated from a
vole many years back in England and, as far as the writer [Sahai] is aware, has been
maintained continuously in artificial culture on an egg medium; at any rate it has
been so maintained since its receipt in this laboratory nearly two years ago. The
vole bacillus, according to A.E. Griffith, is moderately pathogenic for rabbits and
guinea-pigs when inoculated in large doses intraperitoneally or intravenously, but
tests with the strain used in this experiment have shown that it has now become
almost completely avirulent for these animals after maintenance in artificial culture
for so many years. Whether this has anything to do with reducing its immunizing
properties one is not yet in a position to say. Young and Paterson [1949] have shown
that the degree of resistance set up in cattle by vole vaccination was correlated with
the virulence of the vaccinating strain of vole bacillus for its natural host.
The other fact relates to the dose of bovine tubercle bacilli used for testing the
immunity. This dose was decided upon after a good deal of consideration but it
would be open to one to argue whether it was not too large and that any immunity
that might have been developed in the vaccinated animals was perhaps swamped
or obscured by the severe disease that resulted. In this connection it may be
pointed out that 1.0 mgm. of a moist bovine culture has been estimated to contain
nearly 1,000 million bacilli of which at least 10 per cent are viable. On this basis the
number of viable bacilli administered to each animal was about 1,000. The writer
[Sahai] does not consider that this was too large a dose, but the criticism would appear
to be quite legitimate and the point is one which can be decided only by repeating
the experiment using a smaller infecting dose. However, the opinion can perhaps be
ventured that if such a small dose does reveal any differences in resistance between
the vaccinated and the control animals that resistance would probably be of very
low grade and not likely to be of much practical use.
In conclusion, it may be stated that while the experience with the vaccination
of monkeys has not been very encouraging, it seems wise to withhold any final conclu-
sions as to the value of this method of vaccination until the results of the more
important experiment on cattle are available [Sahai].
In order to investigate the possibility of the excretion of bacilli in the milk of
cows vaccinated with the vole bacillus, two virgin heifers and two lactating cows
were administered large and multiple doses (50-100 mg.) of the vole bacillus (LV 285)
intravenously and subcutaneously. Repeated cultural examination of the udder
secretion of the virgin heifers and of the milk of lactating cows did not reveal the
presence of the organism. One of the cows was given the culture directly into its
quarter but still no clinical evidence of infection could be seen. The cows were kept
under observation for a period of 10 to 15 months, and were then destroyed. On
post-mortem examination, none showed any changes, gross or microscopic, sugges-
tive of infection nor the organism, could be recovered from the udder or the suprama-
mmary glands.
Sahai [1943] studied the pathogenicity of a strain (LV 285) of vole bacillus for
the porcupine, which was given 4 mgm. of the culture in the grain. The porcupine