A Mouse Model of Acute Q Fever Following Infection Via A Non-Invasive Intratracheal Inoculation Method

Background: Q fever is a worldwide zoonosis caused by Coxiella burnetii and mainly transmitted by aerosols. This study aims at establishing a systematic and efficient mouse model of acute Q fever via intratracheal (IT) inoculation of aerosolized C. burnetii. Methods: BALB/c mice were infected with C. burnetii via IT route using a non-invasive aerosol pulmonary delivery device to directly place the living C. burnetii organisms into their tracheas. The bacterial loads, pathological lesions, and serological responses were analyzed in mice, and compared with those of mice infected via intraperitoneal (IP) route. Results: As early as at day three post-infection (pi) with a low dose of C. burnetii (1×10⁴ per mouse), a large amount of C. burnetii organisms were determined in blood, lungs, hearts, livers, and spleens of the mice. The inflammatory infiltration was observed in hearts and lungs of mice. Compared with mice infected via IP route, the mice infected via IT route exhibited a higher level of bacterial loads and more severe pathological lesions in hearts and lungs at day 3 and day 7 pi. Conclusions: These data indicated that IT route is more efficient than IP route to cause acute C. burnetii infection in mice. Overall, we successfully established a mouse model of C. burnetii infection via IT route, which is useful for investigations of pathogenesis and immunity of acute C. burnetii infection as well as evaluation of therapeutic drugs and preventive vaccines of Q fever.