Mouse Model for Orientia tsutsugamushi Infection

CD-1 Swiss outbred mice (female, 6–8 weeks of age) were purchased from Charles River Laboratories, Inc. (Wilmington, MA, USA). Mice were initially housed in animal biosafety level (ABSL)-2 laboratories and were transferred to an ABSL-3 laboratory for adaptation one week prior to challenge experiments. Mice were inoculated either intraperitoneally (IP) or intradermally (ID) with10³ MuID₅₀ of O. tsutsugamushi strain Karp (Papua New Guinea) or Woods (Australia) as previously described [34 (link)]. For all ID inoculations, mice were anesthetized using isofluorane (inhalation administration). ID injections of 10³ MuID₅₀ of O. tsutsugamushi were performed at the right ear dorsum at a single site (5 µL of pre-titrated liver-spleen homogenate) using a 0.3 mL insulin syringe (Becton Dickinson, NJ, USA). Negative control animals received an IP or ID inoculation of sterile PBS buffer. Following inoculation, the mice were observed for signs of systemic disease for 21 days. Mice (n = 3–8 per group/time point) were euthanized at 10, 14 (Karp IP only), and/or 21 days following infection. All animal experimentation was performed under the approval of the Institutional Animal Care and Use Committee at the Naval Medical Research Center, Silver Spring, MD (Protocol Number: 11-IDD-26).