A comparison of the virulence in guinea-pigs of South Indian and British Tubercle Bacilli.
Mitchison, D.A.; Wallace, J.G.; Bhatia, A.L.; Selkon, J.B.; Subbiah, T.V.; Lancaster, M.C.
Tubercle; 1960; 41; 1-22.
Dhayagude and Shah (1948) carried out virulence tests in guinea pigs on 24 cultures of tubercle bacilli obtained from Indian patients, and found that some caused generalized tuberculosis whereas others caused only local and glandular lesions. Frimodt Moller, Mathew and Barton (1956) reported that, of 29 cultures from 20 untreated Indian patients and 9 other Indian patients with drug sensitive organisms, to produce involvement of not more than the omentum and hepatic node when guinea-pigs were inoculated in graded doses of from 10 -3 to 10 -6 mg. bacilli by the intraperitoneal route and were killed four and eight weeks later. They suggested that a proportion of Indian cultures of tubercle bacilli were considerably less virulence than European strains. However, when our investigation was started, this conclusion was in doubt for the following reasons. As cultures of known high virulence were not included in their experiments, the apparent attenuation of the Indian organisms could have been caused by a lowered susceptibility to tuberculosis of the guinea pigs employed, or by questions of technique. It is possible that guinea pigs bred for long periods in India and exposed to different environmental conditions and diet from those in the Western Hemisphere might differ in their susceptibility to tuberculosis. Indian cattle have a natural increased resistance to tuberculosis as compared to English cattle (Soparkar, 1925), Secondly atypical mycobacteria may well be more prevalent in tropical than in temperate countries (Palmer, 1953; World Health Organisation Tuberculosis Research Office, 1955) and it is possible that a portion of the strains studied were not tubercle bacilli, as no tests were reported to prove their true identity.
In 1956 the Tuberculosis Chemotherapy Centre was established to investigate problems relevant to the planning of mass domiciliary chemotherapy for tuberculosis by carrying out controlled trials Tuberculosis Chemotherapy Centre, Madras, 1959). As part of the laboratory investigations, the virulence of cultures of tubercle bacilli isolated from the patients in these trials before the start of treatment was determined. The plan was to compare the virulence of British and South Indian cultures and to investigate the relationship between the degree of virulence of the Indian cultures and the clinical findings in the patients from whom they were obtained. The cultures employed were to be obtained from patients who had not received previous chemotherapy for more than two weeks, so that no question would arise that a loss of virulence followed the development of resistance to isoniazid or other chemotherapeutic drugs. All the strains would also be investigated using a variety of identification procedures to ensure that they were tubercle bacilli. Finally, the comparison would be carried out both in India and in Britain on 3 breeds of guinea-pigs to establish that any difference found between the cultures of tubercle bacilli were not influenced by the breed, diet or care of the animals. The results reported here establish that South Indian cultures of tubercle bacilli have a wider range of virulence than British cultures and are, on the average, less virulent.
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