Host-Parasite Relationships in Experimental Airborne Tuberculosis I. Preliminary Studies in BCG-Vaccinated and Nonvaccinated Animals

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Abstract
Previous studies from this laboratory on immunogenicity and allergenicity of defatted myco-bacterial vaccines involved subcutaneous challenge of guinea pigs and killing of the animals 6 weeks later to evaluate the amount of disease. This type of experiment has been discontinued in this laboratory in favor of an airborne challenge type of experiment, with the advantages that animals can be challenged with small numbers of bacilli by a natural route, and the number of primary lesions, the rate of spread from those lesions, and the rate of bacillary multiplication can be used to evaluate protection. Ecperiments to determine uniformity of infection showed that a fair degree of uniformity resulted when 7 guinea pigs were exposed simultaneously, and were studied 3 weeks later to determine numbers of primary lesions and bacilli in the tissues. A less satisfactory degree of uniformity was obtained when more animals were exposed at one time. BCG-vaccinated and nonvaccinated animals were studied to determine the earliest time and the optimal time for killing the animals to detect the effects of vaccination. In guinea pigs, the degree of protection assessed by lesion counts is time-dependent, but the degree of protection assessed by viable counts of bacilli in the tissues was relatively constant 3 to 12 weeks after infection. Mice vaccinated subcutaneously with BCG were not protected against infection at any interval between 2 and 19 weeks. Guinea pigs vaccinated subcutaneously with the same lot of vaccine were protected as judged by counts of viable bacilli in the tissues 3 weeks after infection.