Respiratory infection with attenuated Mycobacterium tuberculosis H37Ra in malnourished guinea pigs

Abstract

Specific pathogen-free guinea pigs were infected via the respiratory route with viable, attenuated Mycobacterium tuberculosis H37Ra and maintained on purified isocaloric diets. The control diet contained 30% protein (ovalbumin) and 50 ppm of added zinc (50 micrograms/g), the low protein diet contained 10% protein and 50 ppm of added zinc, and the low zinc diet contained 30% protein and no added zinc. Guinea pigs from each diet treatment were skin tested with purified protein derivative 48 h before sacrifice at 3, 4, and 5 weeks postinfection. Protein-deficient animals exhibited significantly reduced body weight, spleen weight, serum total proteins, and serum albumin. Zinc deficiency was characterized by loss of weight and progressive reductions in plasma zinc concentrations. The number of viable M. tuberculosis H37Ra cells was significantly higher in the lungs of both malnourished groups at 3 weeks, but fell below control viable counts by 5 weeks postinfection. A similar pattern was seen in the spleens and bronchotracheal lymph nodes. Both the proportion and intensity of delayed hypersensitivity reactions increased steadily between 3 and 5 weeks in control animals, whereas the two malnourished groups were essentially anergic at all intervals, despite systemic infection. These results demonstrate that both protein and zinc deficiencies exert a significant influence on the development of pulmonary tuberculosis but that the nature of the influence depends upon the interval studied. In both malnourished groups, the pulmonary infection tended to peak early and decline, whereas the disease developed more slowly in control animals. Apparent control of mycobacterial populations in the tissues was accomplished by malnourished animals in the absence of demonstrable delayed hypersensitivity.

Mycobacterium bovis BCG vaccine fails to protect protein-deficient guinea pigs against respiratory challenge with virulent Mycobacterium tuberculosis

“…Although we did not skin z w w -j 0. test animals prior to respiratory challenge, previous experience indicates that the protein-malnourished guinea pigs would have been responsive to PPD with reactions similar to those seen at 1 week (12). These observations confirm our previous reports of tuberculin anergy in proteinmalnourished guinea pigs infected with M. bovis BCG and attenuated M. tuberculosis H37Ra (10,12) and support the contention that malnutrition interferes with the diagnostic usefulness of PPD skin tests in individuals with clinical tuberculosis (D. N. McMurray, Editorial, Chest 77: [4][5]1980). Among the most consistent and predictable reports of impaired cell-mediated immune function in malnourished humans have been the observations of failure to develop normal tuberculin skin reactivity after M. bovis BCG vaccination (6,11,16).…”

“…Identical numbers of virulent mycobacteria were recovered from lung, spleen, and lymph nodes of low-protein and control, nonvaccinated groups. We had observed previously that protein-deficient guinea pigs ultimately controlled primary infections with M. bovis BCG or attenuated M. tuberculosis H37Ra as successfully as normally nourished animals (10,12). In those experiments, as in the ones reported here, control of mycobacterial populations in nonvaccinated animals was seen in the absence of significant tuberculin hypersensitivity.…”

“…After 6 weeks on the experimental diets (i.e., 6 weeks postvaccination with M. bovis BCG), all guinea pigs were infected via the respiratory route in an exposure chamber described previously (10,20). The infection was carried out in a biohazard facility for use with class 3 human microbial pathogens.…”

“…Our previous results revealed specific lesions in the immune responses of protein-deficient guinea pigs vaccinated with M. bovis BCG. In general, protein-malnourished guinea pigs failed to mount a significant tuberculin reaction, even to increased doses of tuberculin, although these animals eventually controlled infection with M. bovis BCG and other attenuated mycobacteria (12,10). The experiments we describe here were designed to determine whether protein-malnourished guinea pigs could be protected by M. bovis BCG vaccine against respiratory challenge with virulent Mycobacterium tuberculosis.…”

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

“…Specific dietary deficiencies in humans and experimental animals have significant deleterious effects on cell-mediated immune responses to infection (7). Protein deficiency is accompanied by the loss of tuberculin hypersensitivity to purified protein derivative (PPD) (8,10,22). Experiments have shown increased numbers of virulent mycobacteria in spleens and lungs of previously BCG-vaccinated, malnourished animals challenged by the respiratory route with M. tuberculosis (9, 11).…”