10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Modeling the Aerobiologic Transmission of Tuberculosis: Aerosol Studies using the Nonhuman Primate
RACHEL REDMANN, Stephanie Killeen, Nadia Golden, Deepak Kaushal, Chad J. Roy, Tulane University
Abstract Number: 1663 Working Group: Bioaerosols
Abstract Tuberculosis is an aerosol-acquired pulmonary disease that is caused by exposure to and infection with Mycobacterium tuberculosis (Mtb). Transmission occurs primarily through effective transfer of bacilli-laden respiratory secretions from an infected to naïve host. Tubercular disease is commonly studied using experimental infection in animas that include the rabbit and nonhuman primate. The latter species is considered to be a near-clinical animal model of active pulmonary tuberculosis and is an optimal test system for studying transmission phenomena. The rhesus macaque (Macaca mulatta) represents a highly refined model of clinical tuberculosis, with development of active pulmonary disease that shares remarkable similarities to clinical tuberculosis in humans. The rhesus was subsequently utilized to study transmission and was experimentally aerosol-infected with two strains of Mtb of varying virulence (str. Erdman or CDC1551). Prior to aerosol infection, strain-specific aerosol susceptibility was determined in order to understand environmental survival of laboratory-generated bacilli and to properly target low-dose aerosol animal infection. The Erdman strain of Mtb approximated the comparator low virulence strain CDC1551, with a mean spray factor within 1 log (Erdman: 4.0E-07±2.3E-06; CDC1551; 9.0E-06±6.7E-06). Thereafter, rhesus macaques (n=8) were experimentally infected by small particle aerosol exposure (MMAD=1 μm; σg=1.4) with either Erdman or CDC1551 Mtb each at a target inhaled dose of 250 CFU. Animals were monitored for development of disease over the next 12 weeks, including biological outcome parameters correlative with development of disease (e.g., PPD positivity, C reactive protein, radiographs, presence of bacilli in lavage fluid). Animals were monitored for development of physiological changes, specifically in their exhaled breath throughout the study. Sampling included semi-continuous monitoring of ambient air within specialized input-only HEPA-filtered sealed primate caging units, and weekly face mask-based collection of exhaled breath during physical examination. In addition, respiratory function was measured using whole-body plethysmography. Aerosol parameters measured within the caging units and face masks included cumulative (total) particle counts and distribution-specific data collection. Aerosol samples were also collected using size-selective filters (0.3 μm; 37 mm MCE) in both configurations which were subsequently eluted in media (LB) and cultured for presence of Mtb; split samples were also subjected to PCR for Mtb genomic material. Results showed animals experimentally infected with the virulent strain (Erdman) experienced rapid development of active pulmonary tuberculosis, with a mean of 5-6 weeks before recommended euthanasia. This outcome contrasted to CDC1551-exposed animals, which developed disease at a gradual tempo, averaging 10-12 weeks before termination of study. Physiological changes, specifically respiratory measurements via plethysmography, was largely determinative of the strain of Mtb used for experimental infection. Minute volume (Vm) and frequency (f) doubled within 2-3 weeks of infection in Erdman-infected animals contrasting to CDC1551 animals where similar changes were observed 4-5 weeks post experimental infection. Aerosol monitoring showed a peak in total particles (≈7.0E+06 particles/20 liters) in Erdman-exposed animals at week 4 post-infection whereas particle production peaked in CDC1551-exposed cohorts at week 7-8 post-infection. The distribution of particles collected during infection markedly changed as the disease severity and tempo intensified, with the respirable fraction of particles produced increasing upon culmination of disease across both strains of Mtb used for infection. This study is one of the first to attempt to measure exhaled breath aerosol production during experimental infection with Mtb using a species that produces a near-clinical model of tubercular disease. This approach provides a basis to determine and characterize initiation and production of Mtb in respiratory secretions in the context of tuberculosis disease and represents an expert system by which to study infectious transmission.