Cynomolgus macaque model for pneumonic plague.

A recombinant vaccine (rF1V) is currently being developed for protection against pneumonic plague. An essential component in evaluating efficacy of the rF1V vaccine is the development of a well-understood animal model that shows similarity to human disease. The objective of this study was to determine the inhaled median lethal dose (LD₅₀), evaluate the pathophysiology of disease and identify appropriate study endpoints in a cynomolgus macaque (CM) model of pneumonic plague. Eighteen CMs were challenged by head-only aerosol exposure with seven dosages of Yersinia pestis CO92. An LD₅₀ of 24 colony forming units was estimated using Probit analysis. Disease pathology was evaluated by blood culture, clinical pathology, histopathology and telemetry. CMs that died became febrile following challenge and died 34-92 h after onset of fever. Bacteremia, increased respiration and heart rate, decreased blood pressure and loss of diurnal rhythm were also observed in conjunction with onset of fever. Histopathological examinations revealed significant findings in the lungs (intra-alveolar neutrophils and fibrinous pleuritis) consistent with pneumonic plague. These data indicate that the disease pathology observed in CMs following aerosol exposure to Y. pestis CO92 is similar to that of pneumonic plague in humans. Thus, the CM is an appropriate model to evaluate efficacy of a recombinant F1V vaccine candidate.