title: Development of an Orientia tsutsugamushi Lc-1 Murine Intraperitoneal Challenge Model for Scrub Typhus: Determination of Murine Lethal Dose (MuLD50), Tissue Bacterial Loads, and Clinical Outcomes.
abstract: Currently, no vaccine has been developed to protect humans from naturally acquired heterologous Orientia tsutsugamushi infections. To enhance the validity of vaccine candidates, we are developing a murine chigger challenge model with the O. tsutsugamushi Lc-1-infected Leptotrombidium chiangraiensis Line-1. To this end, an intraperitoneal (i.p.) murine challenge model using an O. tsutsugamushi Lc-1 isolate was developed for eventual validation of the chigger challenge model. We have determined that the murine lethal dose that kills 50% of the challenged mice (MuLD50) of a liver/spleen homogenate developed from O. tsutsugamushi Lc-1-infected ICR Swiss mice to be 10(-6.9). Employing different inoculum doses of this homogenate, the bacterial load using quantitative real-time PCR (qPCR) was determined to range from 60 to 1.6 × 10(5) genome equivalent copies (GEC)/μL of liver and 33.4 to 2.2 × 10(5) GEC/μL of spleen tissue. The clinical outcomes relative to homogenate dose levels followed a dose-dependent pattern. The successful development and characterization of the O. tsutsugamushi Lc-1 i.p. challenge model will assist in the development and validation of a mouse chigger challenge scrub typhus model.
authors.affiliation: 1 Department of Entomology, US Army Medical Component, Armed Forces Research Institute of Medical Sciences , Bangkok, Thailand .
authors.forename: Woradee
authors.initials: W
authors.lastname: Lurchachaiwong
authors.affiliation: 1 Department of Entomology, US Army Medical Component, Armed Forces Research Institute of Medical Sciences , Bangkok, Thailand .
authors.forename: Wesley
authors.initials: W
authors.lastname: McCardle
authors.affiliation: 2 Viral and Rickettsial Diseases Department, Naval Medical Research Center , Silver Spring, Maryland.
authors.forename: Teik-Chye
authors.initials: TC
authors.lastname: Chan
authors.affiliation: 1 Department of Entomology, US Army Medical Component, Armed Forces Research Institute of Medical Sciences , Bangkok, Thailand .
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Schuster
authors.affiliation: 2 Viral and Rickettsial Diseases Department, Naval Medical Research Center , Silver Spring, Maryland.|3 Preventive Medicine and Biometrics Department, Uniformed Services University of the Health Sciences , Bethesda, Maryland.
authors.forename: Allen L
authors.initials: AL
authors.lastname: Richards
mesh_terms: D000818:Animals; D058491:Bacterial Load; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D007274:Injections, Intraperitoneal; D007928:Lethal Dose 50; D008099:Liver / Q000382:microbiology; D051379:Mice; D008813:Mice, Inbred ICR; D012285:Orientia tsutsugamushi / Q000235:genetics / Q000502:physiology*; D012612:Scrub Typhus / Q000382:microbiology*; D013154:Spleen / Q000382:microbiology; D014324:Trombiculidae / Q000382:microbiology*
keywords: Chigger mite; Modeling; Rickettsia; Scrub typhus; Tsutsugamushi