Effect of Exogenous Superinfection on Naturally Acquired Bovine Tuberculosis in Inbred Rabbits. ∗

Abstract

Summary and Discussion

Under conditions of natural intense exposure to virulent bovine bacilli, rabbits of high and low genetic resistance to tuberculosis were not benefited by cessation of the exposure after the onset of the disease. The disease pursued its characteristic course whether exogenous superinfection took place or not.

That the course of the disease in the rabbits of low genetic resistance was not affected by the cessation of exposure after the onset of the disease may have been anticipated from previous data 2 where it was shown that in the C family the disease pursued the same fulminating course whether acquired under conditions of high or low intensities of contagion. In the resistant family A interruption of the contagion after the onset of the disease tended to retard somewhat the progression of the disease. However, the difference was slight. It is clear therefore that exogenous superinfection after the acquisition of a positive tuberculin reaction does not explain the intensification of the dissemination of the disease and the shortening of the duration observed in this family, with increasing concentrations of bacilli in their environment. It is possible that the initial inhalation of larger numbers of bacilli which do not at once give rise to visible pulmonary foci under high intensities of contagion may account for the more rapid progression of the disease in this family under these conditions.

It is noteworthy that while the differences between the rabbits of high and low resistance to tuberculosis were greatly diminished by the intense contagion prevalent in these experiments, they were not completely wiped out. As in previous studies the A rabbits tended to acquire tuberculin sensitivity more rapidly than the C rabbits, their allergy was less developed during the course of their disease and the progression of the infection was slower and anatomically more chronic.