30 VOLE
VACCINATION
[Vol. XXIII, Part, I,
infection, had the same survival time as the controls, whereas animals vaccinated
thirty-three and forty-three days before infection survived significantly longer
than the controls.
While repeating, the experiments of Wells and Brooke, Birkhaug [1946] allowed
vaccinated and control animals to survive as long as the virulent tuberculous in-
fection would permit. He gave the immunising dose of vole bacilli and B.C.G.
intracutaneously as against the subcutaneous route used by Wells and Brooke.
He observed that the animals vaccinated with vole bacilli and with B.C.G. showed
a pronounced increase in the survival time as compared with the controls, but there
was no marked difference between the two groups of vaccinated animals. All
vaccinated animals as well as the controls died of generalised tuberculosis.
Paterson, Crombie and Coles [1949] vaccinated one group of 50 guinea-pigs
with vole bacilli killed by ultra-violet light, a second group of 50 with B.C.G. and
a third group of the same size were held as controls. The guinea-pigs of all the
groups were given a challenge dose of 0.25 mgm. of human tubercle bacilli by the
subcutaneous route 28 days after the last injection of vaccine. The control group
survived: for an average of 33 days, the vole vaccine group for 64 days, and the B.C.G.
group for 73 days. The difference in survival times was particularly impressive
at the 58th day, when all the controls had succumbed while; only 49 per cent of the
B.C.G. group and 59 per cent of the vole group had died.
It seemed that the degree of protection afforded by the killed vaccine was
comparable to that obtained with B.C.G. The results have been encouraging and
warrant further work since the advantages of a vaccine made from dead organisms
only are obvious.
Young and Paterson [1949] carried out a series of experiments to study the
efficacy of vaccination with the vole acid-fast bacillus against tuberculosis in cattle
by employing a single dose of vaccine intravenously as well as two-spaced doses;
the efficacy of multiple puncture skin vaccination was also determined. They
further compared the types of tuberculous lesions found in vaccinated and un-
vaccinated cattle, and studied the superimposition of infection with vole bacilli
on cattle already infected with bovine tuberculosis. They also recorded the clinical
effects of inoculation of vole bacillus into cattle and carried out bacteriological and
histological examination of the tissues of such calves.
According to them there was little hope for the bestowal on an animal of a
life-time immunity against tuberculosis by vole vaccination, but surely the vole
bacillus was entitled to be ranked alongside B.C.G. as a prophylactic agent. A
single intravenous inoculation of 5 mgm. of vole bacillus could raise the resistance of
cattle to infection with the bovine bacilli to a high degree, this resistance being
evidenced by a complete absence or by a marked diminution in the severity of
lesions following exposure to artificial or natural infection. The resistance took
time to develop, reached its maximum between 6 to 18 months after vaccination
and then slowly waned. The resistance induced by a single inoculation was, how-
ever, of insufficient duration in many animals to warrant the practice of single vac-
cination being used in the field except in special circumstances. They also observed
that revaccination could intensify resistance provided it was delayed until the end of
the fourth week. Further work is being carried out by Young and Paterson to study