Surveillance of vector-borne infections: Dogs as sentinel animals for Orientia and Rickettsia exposure in five regions in Chile

Domestic dogs have been proposed as sentinels for various infectious diseases, including rickettsial infections. In Chile, the only endemic human rickettsiosis is scrub typhus caused by Ca. Orientia chiloensis, an emerging infectious disease, discovered in recent years in southern Chile. The geographic distribution of scrub typhus and other rickettsial infections across Chile is incompletely understood. This study using domestic dogs as sentinel investigated the potential exposure to members of the three main groups of rickettsiae, scrub typhus orientiae (STGO), spotted fever group rickettsiae (SFGR) and typhus group rickettsiae (TGR), in northern, central, and southern Chile. Serological analyses for STGO, SFGR, and TGR were conducted on 1097 dogs from rural and urban areas, which were sampled during 2010 to 2016 in five Chilean regions using a cross-sectional household-based design. Household and dog-level variables were assessed to investigate retrospectively associated risk factors for rickettsial exposure. Overall seroprevalences were 13.8% for STGO, 1.2% for SFGR, and 1.0% for TGR. Higher seropositivity for STGO was associated with dogs from rural areas, male dogs, older dogs, and dog infestation with ticks. Canine seroreactivity to STGO was found across Chile, including regions not known as endemic for scrub typhus. Absence of external deworming was a significant risk factor for SFGR. The present results suggest that during the study period dogs were exposed to rickettsiae over a broader geographic range than previously recognized. Future epidemiological, ecological, and clinical studies are required to confirm the distribution of Orientia species and potential endemicity of other rickettsiae in Chile. • Dogs showed 13.8% seroprevalence to scrub typhus group orientiae (STGO), indicating Orientia exposure across five regions of Chile. • Dogs had low levels of seroprevalence to other rickettsial pathogens. • Rural, male, older, and tick-infested dogs had higher STGO seropositivity rates. • Dogs are effective sentinels for emerging rickettsial infections.