SENSITIVITY of human populations to human and avian tuberculins.

In reviewing the development in veterinary practice of comparative testing with tuberculins prepared from different types of mycobacteria for the purpose of separating cattle with specific and non-specific tuberculin sensitivity, it appeared that similar methods might be useful for the analogous problem of separating specific and non-specific tuberculin sensitivity in human populations. The results of a preliminary investigation along this line are reported in the present paper.Working in several parts of India, a special TRO research team tested more than 3,000 persons with serial doses of both a human and an avian PPD tuberculin corresponding to 1, 10, and 100 TU. An additional 6,000 were tested only with serial doses of human tuberculin.Presumptive evidence of non-specific sensitivity in some of the populations was found from the results of the tests with human tuberculin. Discrepancies in the frequencies of weak-dose and strong-dose reactors in different geographic areas, together with evidence from previous studies, suggested that most of the persons with strong-dose reactions could be regarded as having non-specific tuberculin sensitivity.RESULTS OF COMPARATIVE TESTS WITH HUMAN AND AVIAN TUBERCULINS FURTHER INDICATED THAT THE TUBERCULIN SENSITIVITY IN THE POPULATIONS STUDIED MUST BE CAUSED BY DIFFERENT SENSITIZING AGENTS: one producing a high degree of sensitivity brought out more effectively by the human than by the avian tuberculin, the other producing a low degree of sensitivity brought out more effectively by the avian than by the human tuberculin. The groups with high-grade sensitivity-those who react to the weak-dose test-can undoubtedly be regarded as having specific sensitivity, the kind caused by infection with virulent tubercle bacilli; the group who react only to the 100 TU test have apparently been sensitized by a different agent (or agents). Though the identity of the non-specific agent is still unknown, its antigenic properties would seem to be more closely related to avian than to human tuberculin.