Eco-epidemiology of rodent-associated trombiculid mites and infection with Orientia spp. in Southern Chile

BackgroundScrub typhus is a potentially severe infection caused by bacteria of the genus Orientia, endemic in Asia-Pacific and recently discovered in southern Chile. The presented study aimed to determine the prevalence and species richness of rodent-associated trombiculid mites and their infection with Orientia spp. in different areas of two regions in southern Chile. Methodology/Principal findingsDuring summer 2020, trombiculid mites were collected from rodents captured in three areas in southern Chile known to be endemic for scrub typhus (Cochamo and Chiloe Island in the Los Lagos Region and Tortel in the Aysen Region). A total of 132 rodents belonging to five species were captured using Sherman-like traps; 89.4% were infested with trombiculids. Mite specimens were morphologically identified and subsequently tested by Orientia-specific qPCR. Six mite species were identified. Among chigger-infested rodents, 33.9% carried Orientia-positive mites; this rate was higher in Tortel (63.8%) than in Cochamo (45.0%) and Chiloe Island (2.0%). The analysis of individual mites (n = 901) revealed that 31.2% of Herpetacarus antarctica samples (n = 202) were positive for Orientia DNA; the prevalence was 7.0% in Paratrombicula neuquenensis (n = 213), 6.9% in Herpetacarus eloisae (n = 144), 3.6% in Argentinacarus expansus (n = 55), and 0% in Paratrombicula goffi (n = 110) and Quadraseta chiloensis (n = 177). The southernmost site (Tortel) showed the highest rates of trombiculid infestation, trombiculid load, and Orientia infection in the captured rodents. Conclusions/SignificanceOur study provides new insights into the trombiculid fauna and prevalence of Orientia in mites collected from wild rodents in southern Chile. Orientia DNA was detected in four of the six mite species. Rates of infestation, mite loads, and Orientia prevalences differed geographically and were highest in the Aysen Region. Our data improve our knowledge on possible vectors of scrub typhus and their distribution in Chile. Author summaryScrub typhus is an emerging zoonotic infection caused by Orientia species in Asia-Pacific and recently discovered in Chile. The disease is transmitted by chigger mites; however, the knowledge on the vectors in Chile is scarce. We undertook a field study to capture wild rodents in three areas in southern Chile and to determine their infestation with chiggers infected with the bacteria. The study revealed that 89.4% of rodents carried trombiculid mites belonging to six species. The mite fauna and prevalence of Orientia showed geographical variations. Orientia DNA was found in four chigger species, mainly in two species of the genus Herpetacarus. The southernmost study area showed the highest prevalence of trombiculid infestation and infection with Orientia and must be considered a hot spot for scrub typhus in Chile. This study provides important new knowledge on the eco-epidemiology of scrub typhus in Chile.

Automated summary

This study aimed to determine the prevalence and species richness of rodent-associated trombiculid mites and their infection with Orientia species in southern Chile. The study found that 89.4% of rodents were infested with trombiculids and 33.9% carried Orientia-positive mites.