186
Bovine Tuberculosis
The environmental conditions appertaining to
cattle husbandry in the tropics as compared
with colder climates has on occasions been
brought forward to explain these circumstances
[Hornby, 1934], but, as pointed out earlier,
this cannot be accepted as the true explanation.
The tubercle bacillus as found in Zebu cattle has
been said to be of lower virulence than normal
[Sheather, 1921], but when the literature is dis-
cussed it will be seen that there is little evidence
to support this contention, whilst in Uganda
numerous bovine strains have been isolated from
infected cattle and all have proved to be of standard
virulence.
Lastly the question of race resistance has been
investigated and it appears it is here where the
true explanation lies.
Experimental evidence points to the fact
that Zebu cattle possess a considerably greater
resistance to tubercular infection than those of
European breeds in so far as standard European
strains of the tubercle bacillus are concerned.
LITERATURE
Liston and Soparkar [1917], referred to in part
I of this paper, concluded as the result of their
experiment that the comparative infrequency of
the disease among cattle in India is due to natural
resistance rather than to any method of housing
or keeping cattle in. India as compared with
England. They also point out that whereas a
dose of 50 mg. of a culture of tubercle bacillus
when injected into English calves invariably
causes severe generalized tuberculosis, this does
not apply to Indian calves, where there appears
to be a much greater individual variation in
resistance.
Sheather [1921] carried out inoculation experi-
ments on buffalo and cow calves, using a local
strain of tubercle bacilli isolated from a tubercu-
lous bovine. Five buffalo calves received 10 mg.
of culture subcutaneously and five received 50
mg. Twelve cow calves were similarly inoculated,
half receiving 10 mg. of culture and half 50 mg.
None of these animals died of the inoculation and
they were killed off between 152 and 159 days later.
All animals put on weight and the post-mortem
examinations were classified as follows:
(a) Fourteen animals
Slight tuberculosis.
A lesion at the site of inoculation.
Lesions in the thoracic glands and pos-
sibly abdominal glands.
A few lesions in the lungs or spleen.
(b) Five animals
Extensive but not severe.
As above, but with the addition of tuber-
culous pleurisy or peritonitis or both.
(c) Three animals
Generalized but not progressive. Cases in
which there was evidence of invasion of
the organs by way of the blood streams
with the production of numerous lesions
in the lungs.
The results are compared with those of the
Royal Commission on Tuberculosis (2nd interim
Report, Part II Appendix, Vol. I, p. 34), which
showed that a subcutaneous dose of 50 mg. of
culture almost invariably produced fatal gene-
ralized tuberculosis within seven weeks and in
the case of a 10 mg. dose 60 per cent died within
eight weeks.
The author concludes from his experiments
both on rabbits and on cattle that the virulence
of the tubercle bacillus isolated from Indian
cattle is lower than that isolated from cattle in
Europe. He states:
'Glen Liston's experiments indicated that Indian
cattle are less susceptible to infection with
the tubercle bacillus than English animals when
tested with a virus of European origin.'
'The experiments here recorded indicate that
this is not the sole or possibly even the most
important factor in determining the comparatively
frequent occurrence of tuberculosis in Indian
cattle. They appear to
indicate
beyond
all possibility of doubt that the strains of tubercle
bacilli affecting cattle in India possess a distinctly
lower degree of virulence than tubercle bacilli
iosolated from cattle in Europe.
'A point which would appear to support the
view that the lower virulence of the organism is
the more important factor is that in practically
every instance the natural lesions which have
come under observation have been restricted
to a few glands and have been to a very large
extent calcified.'
Soparkar [1926] carried out a large-scale
experiment to test the susceptibility of various
Indian breeds of cattle to tuberculosis. A type
strain obtained from the National collection was
used in a dose of 50 mg. inoculated subcutaneous-
ly. One hundred and forty-one calves were used
in the experiment, and the results showed
that whilst a considerable number (48) proved
very resistant and remained well and lived
beyond 90 days, the susceptibility varied consider-
ably. Ninety-three died of acute generalised
tuberculosis in periods varying from 17 to 101
days. Apparently out of these 93, only 10
showed the very severe type seen in English
calves.
The author summarizes the position in the
following paragraph:
' While the experiments of the Royal Commis-
sion on Tuberculosis show that a dose of