Indoor and Outdoor Rodent Hosts of Orientia tsutsugamushi, Shandong Province, China

During December 2012–July 2016, we tested small indoor and outdoor mammals in Qingdao, China, for Orientia tsutsugamushi infection. We found that outdoor Apodemus agrarius mice, Cricetulus barabensis hamsters, and Niviventer confucianus rats, as well as indoor Mus musculus mice, tested positive for O. tsutsugamushi by PCR.

S crub typhus is an emerging infectious disease caused by Orientia tsutsugamushi (1), which is transmitted through the bites of infected chiggers, the larvae of trombiculid mites of the genus Leptotrombidium. Scrub typhus has been documented in southern China for thousands of years (2) and emerged in northern China during the 1990s (3). Several studies have investigated the animal hosts of O. tsutsugamushi (4,5), but the major hosts and seasonality of O. tsutsugamushi in northern China remain unclear. We collected small animals in Qingdao, a city in eastern China, to investigate the hosts and seasonality of O. tsutsugamushi.
All infected rodents were captured during autumn (i.e., September-November); among rodents captured in autumn, the infection rate was 8.1%  tsutsugamushi. R. norvegicus rats, which were mainly captured indoors, were all negative for O. tsutsugamushi; these findings suggest that these rats might primarily stay indoors, thereby avoiding exposure to chiggers in the fields. We found 2 (11.1%) O. tsutsugamushi-positive indoor house mice, possibly reflecting their travels between house and field.
The sequences of O. tsutsugamushi from rodents identified belonged to 2 lineages, Kawasaki and STA-07 (Figure). We identified the Kawasaki strain in 4 rodent species collected in the same village during the autumns of 2013 and 2014 and the STA-07 strain in A. agrarius mice in a village 20 km away during the autumn of 2014. These results suggest that O. tsutsugamushi isolates from same geographic area are highly homologous regardless of host species. We deposited the 56-kDa type-specific antigen gene sequences obtained in this study in GenBank (accession nos. MT833389-95).
In conclusion, we documented O. tsutsugamushi infection among outdoor A. agrarius mice, N. confucianus rats, and C. barabensis hamsters, as well as indoor M. musculus mice, in Shandong Province; these rodents might serve as animal hosts for O. tsutsugamushi. The finding of O. tsutsugamushi infection among indoor mice suggest that persons might be exposed to chiggers and O. tsutsugamushi at home. Further study is needed to investigate whether scrub typhus patients in the area had a history of working or traveling in the fields and whether their houses were infested with mice and chiggers. Our results indicate that physicians should be attentive to patients who might have O. tsutsugamushi infection, even if those patients have not worked in the field.

About the Author
Ms. Li is a doctoral candidate at Shandong University, Jinan, China. Her research interests include emerging infectious disease and vector-borne disease.