34
VOLE
VACCINATION
[Vol. XXIII, Part I,
antigen? Wallgren considers that it is not inconceivable that the B.C.G. may be-
come so avirulent as to have no effect. However, the staunch advocates of B.C.G.
vaccination fail to appreciate this view and consider this strain to be a 'virus fixe'.
But this will have to be agreed by them that much of our knowledge on this strain
during recent year is based on circumstantial evidence gained by the vaccination
of millions of human beings and none of the many reports published after 1930—
when a progressive fall in antigenic properties is feared-claims individually to give a
convincing proof of the real protective value of B.C.G., may be that it is so because
much work under controlled conditions in the veterinary field has not been done
since then and to plan a controlled experiment in tuberculosis vaccination in man
is a matter of so much difficulty as to be virtually impossible. However, there is a
strong presumptive case even at this stage for the effectiveness of B.C.G. vaccination
in raising resistance to subsequent infection, but there seems to be no authentic
documentary evidence to show that the strain is not gradually falling down in
virulence and perhaps also in its antigenic value. But it is clear at any rate that
this vaccine is rational, safe and brings about tuberculin sensitivity.
According to Wells, 'the fact that the vole bacillus is not attenuated by culti-
vation in vitro, and that the virulence for voles can be maintained indefinitely by
passage seems important'.
Considering all the above facts, it seems that the vole vaccination compares
very favourably with the B.C.G., and perhaps a hope can be expressed that one day
it may supplant B.C.G. in view of its being a naturally occuring muring type of
tubercle bacillus. A more detailed, and critical study of the vole vaccine is therefore,
very necessary, needs no emphasis.
The very useful work already done with this organism has opened fresh and
maiden fields for investigation and it is high time that studies on vole vaccination
again receive a fresh stimulus in this country, so that India could contribute its
share of research into this vital and a very important problem of human as well as
livestock welfare.
It is true that mass vaccination, may be with B.C.G. or vole bacillus, is not going
to find any very important place in the programme of eradication of tuberculosis
from the livestock of any country, but surely it will have its way in as much as it
can be profitably and advantageously employed for the control and even eradication
of this scourage from heavily infected dairy herds and areas from which a large number
of reactors cannot be cast at one time on economic grounds. No doubt an infallible
way of eradicating tuberculosis will be to segregate all the carriers of tubercle bacilli
and thus eliminate the seedbeds of contagion. Yet, to continue to be logical, it
has to be frankly admitted that for years together a method like this will pay dimi-
nishing returns the more vigorously it is enforced, especially on heavily infected
farms in countries where the incidence is high. To be practical and realistic, there-
fore, it would seem that some procedure of vaccination, which could lead to an
enhanced resistance over a number of years would have to go hand in hand at-
least in the heavily infected farms with the systematic segregation of known sources
of open infection in order to build up an artificial herd or area immunity. The
entire milking herds of the farms or areas in a tight grip of tuberculosis, where-from
positive cases cannot be removed without seriously affecting the milk production,