Caseation and Softening in Tuberculosis of Vaccinated and Unvaccinated Guinea Pigs

Abstract

There is much evidence that vaccination with the BCG strain of the tubercle bacillus produces a certain degree of resistance to reinfection with virulent tubercle bacilli. The question has been raised, however, as to whether the allergy resulting from such vaccination might be a factor in producing a more extensive and more destructive type of tuberculosis. In an experiment to ascertain if any relationship exists between allergy and the character of the tuberculous lesions, one series of guinea pigs was injected subcutaneously in the left inguinal region with 5 mg. of the BCG culture, a second series was injected in a similar manner with 30 mg. of the virulent Ravenel strain of bovine tubercle bacillus killed by heating for 1 hour at 70°C., and a third group of unvaccinated guinea pigs were used as controls.

Six weeks after vaccination the sensitivity of these animals to old tuberculin was determined by injecting into the skin of each animal, at widely separated points, 1, 5 and 10 mg. of old tuberculin, and reading the results 48 hours later. It was found that among the 14 guinea pigs of the first series, injected with BCG, 9 reacted to 1.0 mg. of tuberculin and 5 to 5.0 mg. Of the 15 guinea pigs of the second series, injected with the heat-killed tubercle bacilli, 3 reacted to 1.0 mg. of tuberculin, 6 to 5.0 mg., 5 to 10.0 mg., and one failed to react. The 11 untreated control guinea pigs did not react to the injection of tuberculin. The vaccinated as well as the unvaccinated control animals were then injected intratracheally while under ether anesthesia with approximately 100 tubercle bacilli of the virulent Ravenel bovine strain. Six weeks later all of the animals were killed and necropsied.