Efficacies of BCG and vole bacillus (Mycobacterium microti) vaccines in preventing clinically apparent pulmonary tuberculosis in rabbits: a preliminary report

Tuberculosis (TB) kills more people in the world today than any other infec tious disease, and the number of drug-resistant Mycobacterium tuberculosis isolates is increasing. Vaccines, better than most of the currently availab le strains of bacille Calmette-Guerin (BCG), are urgently needed to control this disease. TB in rabbits resembles human TB more closely than TB in any other common laboratory animal and a most pertinent method of assessing va ccine efficacy is Lurie's tubercle count method in this species. Vaccinated and control rabbits were infected by aerosol with virulent human-type tube rcle bacilli (H37Rv). At necropsy 5 weeks thereafter, the grossly visible p rimary tubercles in the entire lung were counted. A decrease in the number of such tubercles is a quantitative measure of vaccine efficacy: An effecti ve vaccine prevents microscopic tubercles from growing to grossly visible ( clinically apparent) size. The Pasteur substrain of BCG and two substrains of Mycobacterium microti (the vole bacillus) reduced the number of visible primary tubercles an average of 75%, whereas three other substrains of BCG and three other substrains of vole bacilli only reduced the number an avera ge of 40%. These initial studies indicate that Lurie's tubercle-count metho d in rabbits is a precise way to choose the best available tuberculosis vac cines. (C) 2000 Elsevier Science Ltd. All rights reserved.