Fig 1. Outbred CD-1 mice were highly susceptible to O. tsutsugamushi infection.

CD-1 and C57BL/6 mice were inoculated i.v. with O. tsutsugamushi Karp strain (5.6×10⁴ FFU, 10/group) or PBS (mock, 3/group) and monitored daily for signs of illness. (A) CD-1 mice began to succumb to infection on day 9, and all died by day 12. Only 10% of C57BL/6 mice died by day 15, with the rest surviving. (B, C) Body weight loss in CD-1 mice was rapid and progressive, in comparison to that of C57BL/6 mice. (D) CD-1 mice showed disease score on day 5 and had the highest score on day 12. In contrast, C57BL/6 mice started to recover at day 11. Log-ranked (Mantel Cox) test was used for statistical analysis of survival. ****, p < 0.0001.