Arthropod-borne rickettsial pathogens cause mild and severe human disease worldwide. The tick-borne pathogen Rickettsia parkeri elicits skin lesions (eschars) and disseminated disease in humans; however, inbred mice are generally resistant to infection. We report that intradermal infection of mice lacking both interferon receptors (Ifnar1-/-;Ifngr1-/-) with as few as 10 R. parkeri elicits eschar formation and disseminated, lethal disease. Similar to human infection, eschars exhibited necrosis and inflammation, with bacteria primarily found in leukocytes. Using this model, we find that the actin-based motility factor Sca2 is required for dissemination from the skin to internal organs, and the outer membrane protein OmpB contributes to eschar formation. Immunizing Ifnar1-/-;Ifngr1-/- mice with sca2 and ompB mutant R. parkeri protects against rechallenge, revealing live-attenuated vaccine candidates. Thus, Ifnar1-/-;Ifngr1-/- mice are a tractable model to investigate rickettsiosis, virulence factors, and immunity. Our results further suggest that discrepancies between mouse and human susceptibility may be due to differences in interferon signaling.
All data sets generated or analyzed during this study are included in the manuscript and supporting files.
- Matthew D Welch
- Matthew D Welch
- Eva Harris
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Animal experimentation: Animal research was conducted under a protocol approved by the University of California, Berkeley Institutional Animal Care and Use Committee (IACUC) in compliance with the Animal Welfare Act and other federal statutes relating to animals and experiments using animals (Welch lab animal use protocol AUP-2016-02-8426). The University of California, Berkeley IACUC is fully accredited by the Association for the Assessment and Accreditation of Laboratory Animal Care International and adheres to the principles of the Guide for the Care and use of Laboratory Animals. Mouse infections were performed in a biosafety level 2 facility. All animals were maintained at the University of California, Berkeley campus, and all infections were performed in accordance with the approved protocols. Mice were immediately euthanized if they exhibited severe degree of infection, as defined by a core body temperature dropping below 90˚ F or lethargy that prevented normal movement.
- Kim Orth, HHMI/University of Texas Southwestern Medical Center, United States
© 2021, Burke et al.
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