Effects of diet and genetics on Mycobacterium bovis BCG vaccine efficacy in inbred guinea pigs.

Strain 2 and strain 13 guinea pigs were vaccinated with Mycobacterium bovis BCG and placed on low-protein or protein-adequate diets. Five weeks later all animals were infected by the respiratory route with virulent Mycobacterium tuberculosis H37Rv organisms. Four weeks postchallenge, guinea pigs were skin tested with purified protein derivative and sacrificed. Protein deficiency resulted in significant reductions in body weight and thymus weight and in an impairment in the ability to control the M. bovis BCG vaccine organisms and to mount delayed hypersensitivity reactions. Protein deficiency also adversely affected the efficacy of the BCG vaccine as demonstrated by the numbers of virulent organisms recovered in spleens and lungs. Strain differences were observed in the number of leukocytes, thymus weight, and the responsiveness of blood lymphocytes to purified protein derivative stimulation. In general, strain 13 guinea pigs responded more dramatically to dietary insult than did their strain 2 counterparts. Protein deprivation completely abolished BCG vaccine protection in the lungs and spleens of strain 13 animals and significantly reduced the protection afforded to strain 2 animals. In both strains, the BCG vaccine protected normally nourished guinea pigs. There was no significant difference between strains with respect to susceptibility to pulmonary infection with virulent mycobacteria. Thus, diet and genetic pedigree each had a significant influence on BCG vaccine efficacy.