NONHUMAN PRIMATE MODEL OF MELIODOSIS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Melioidosis is an infectious disease caused by exposure to Burkholderia pseudomallei, a saprophyte found primarily in Southeast Asia and Northern Australia. Melioidosis is considered an emerging infectious disease and epizoonotic agent. Incidence of B. pseudomallei-associated bacterial sepsis and bronchopneumonia has significantly increased in endemic areas over the past decade. B. pseudomallei is a biological threat agent primarily because of its remarkable infectivity at a low (less than 100 bacterial cells) dose. As a result, the Centers of Disease Control and Prevention (CDC) have identified B. pseudomallei as a select biological agent, with a high potential for misuse against masses. Melioidosis is associated with a severe clinical syndrome which is dependant in part on the route of exposure, dose, and immune status of the host, although much remains unclear about pathogenesis of the disease. Although infection from subcutaneous inoculation is not uncommon, inhalation produces the most severe disease. Presently, in vivo study of melioidosis has been mostly restricted to rodent disease models (e.g., hamster, guinea pig). Molecular genetic studies coupled with rodent disease models have implicated genes encoding Inv/Mxi-Spa-like Type III secretion system bsa, alternate and stationary phase sigma factor R SOS responder recA in mediating virulence and protection from host immune response. No nonrodent model (other than equine) have been identified or characterized to further study this disease. Although intensive vaccine discovery and therapeutic development is ongoing, there has been minimal research into a nonhuman primate disease model to support these studies. As such, a nonhuman primate model would represent a significant tool to further define pathogenesis and study the clinically relevant parameters of the disease. Moreover, the establishment of a nonhuman primate model will also allow researchers to study the phenotype of B. pseudomallei mutants that exhibit loss of virulence in rodent models, in a more appropriate human-like model. It is conceivable that such B. pseudomallei strains carrying multiple lesions will serve as potential vaccine candidates. The goals of this project are to define a nonhuman primate model that emulates the reported pathophysiology of human melioidosis when inhaled, to identify molecular correlates in the bacterium during host-infection and conditions that mimic it; and define immunological parameters associated with the disease. The severe clinical symptom of melioidosis is dependant in part on the route of exposure, dose, and immune status of the host, although much remains unclear about pathogenesis of the disease. To address this gap, we performed a study to develop an aerosol exposure method for induction of melioidosis in rhesus macaques (Macaca mulatta) and characterize the pneumonic form of the disease. Six rhesus macaques were experimentally exposed by small particle aerosol to 10^3 to 10^6 CFU of Burkholderia pseudomallei 1026b. One animal succumbed to disease +7d postinfection; all other animals were euthanized at day 30 (1) or 45 (4). Gross and microscopic lesions, bacterial burden in lungs and blood, and histologic changes were evaluated. Results of aerosol exposure to B. pseudomallei proved lethal (8 days) at the highest inhaled doses (H10^6 CFU); lower doses resulted in a localized pulmonary bacterial infection clinically similar to bacterial pneumonia. Grossly, the one animal succumbing to disease +7d PI was characterized as a severe pneumonia with focal necrotizing lesions in the tracheal mucosa, adrenal and bronchial lymph nodes. Histologically, there was severe subacute fibrinopurulent inflammation, edema, hemorrhage, and necrosis in the lung. Milder acute congestion was observed in the liver, with mild to moderate necrosis in the tracheal mucosa, adrenal cortex, axillary, and bronchial lymph nodes. The other animals showed minimal histologic changes at the time of necropsy. An attempt to initiate bacterial recrudescence in convalescent animals via CD8+ lymphocyte depletion failed, suggesting that CD8+ lymphocytes play a minimal role in controlling B. pseudomallei infection. Pathologic findings in rhesus macaques after aerosol exposure to B. pseudomallei show a dose-related gradient for infection and are comparable to clinical cases of the pneumonic form of the disease in humans.