Experimental aerosolized guinea pig-adapted Zaire ebolavirus (variant: Mayinga) causes lethal pneumonia in guinea pigs.

Eight guinea pigs were aerosolized with guinea pig-adapted Zaire ebolavirus (variant: Mayinga) and developed lethal interstitial pneumonia that was distinct from lesions described in guinea pigs challenged subcutaneously, nonhuman primates challenged by the aerosol route, and natural infection in humans. Guinea pigs succumbed with significant pathologic changes primarily restricted to the lungs. Intracytoplasmic inclusion bodies were observed in many alveolar macrophages. Perivasculitis was noted within the lungs. These changes are unlike those of documented subcutaneously challenged guinea pigs and aerosolized filoviral infections in nonhuman primates and human cases. Similar to findings in subcutaneously challenged guinea pigs, there were only mild lesions in the liver and spleen. To our knowledge, this is the first report of aerosol challenge of guinea pigs with guinea pig-adapted Zaire ebolavirus (variant: Mayinga). Before choosing this model for use in aerosolized ebolavirus studies, scientists and pathologists should be aware that aerosolized guinea pig-adapted Zaire ebolavirus (variant: Mayinga) causes lethal pneumonia in guinea pigs.

The pathology of experimental anthrax in rabbits exposed by inhalation and subcutaneous inoculation.

OBJECTIVE: Although rhesus monkeys are considered to be an appropriate model for inhalational anthrax in humans, an alternative for vaccine and therapeutic efficacy studies is desirable. This study characterized the pathology of lethal anthrax in rabbits challenged by subcutaneous inoculation and aerosol exposure. MATERIALS AND METHODS: New Zealand white rabbits were exposed by subcutaneous inoculation or aerosol to lethal doses of Bacillus anthracis spores. RESULTS: The pathology of anthrax in rabbits exposed by either route was similar, with principal findings occurring in the spleen, lymph nodes, lungs, gastrointestinal tract, and adrenal glands. The cardinal changes were hemorrhage, edema, and necrosis, with bacilli and limited leukocytic infiltration. Features that depended on the route of exposure included mediastinitis in aerosol-exposed rabbits, a primary dermal lesion after subcutaneous inoculation, and differences in the pattern of lymph node involvement. Lesions observed in rabbits were comparable to those of inhalational anthrax in humans and rhesus monkeys. Noteworthy differences included the lack of leukocytic infiltration in brain and meningeal lesions, the relatively mild mediastinal lesions, and a lower incidence of anthrax-related pneumonia in rabbits compared with humans. These differences may be attributed to the greater susceptibility of rabbits to anthrax. Increased susceptibility is associated with both reduced leukocytic response to the bacilli and a more rapid progression to death, which further limits development of leukocytic infiltrates in response to the basic lesions of hemorrhage and necrosis. Primary pneumonic foci of inhalational anthrax, which may be influenced by preexisting pulmonary lesions in humans, were not observed in our rabbits, which were free of preexisting pulmonary disease. CONCLUSION: Anthrax in rabbits may provide a useful model for evaluating prophylaxis and therapy against inhalational anthrax in humans.

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 infectious disease, and the number of drug-resistant Mycobacterium tuberculosis isolates is increasing. Vaccines, better than most of the currently available strains of bacille Calmette-Guérin (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 vaccine efficacy is Lurie's tubercle count method in this species. Vaccinated and control rabbits were infected by aerosol with virulent human-type tubercle bacilli (H37Rv). At necropsy 5 weeks thereafter, the grossly visible primary tubercles in the entire lung were counted. A decrease in the number of such tubercles is a quantitative measure of vaccine efficacy: An effective 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 average of 40%. These initial studies indicate that Lurie's tubercle-count method in rabbits is a precise way to choose the best available tuberculosis vaccines.