Molecular epidemiology of Orientia tsutsugamushi in chiggers and ticks from domestic rodents in Shandong, northern China.
BACKGROUND
Scrub typhus is endemic to a 13,000,000-km² area of the Asia-Pacific region, and causes an annual incidence of 1 million people. The mortality rate of scrub typhus ranges from 6.1% to 25% in Southeast Asia. Natural infection of Orientia tsutsugamushi has been identified in domestic rodents in Shandong Province. However, infestation of chiggers and ticks on the domestic rodents and prevalence and genotypes of O. tsutsugamushi in these Acarina remain unclear.


METHODS
During September 2010 to March 2012, 3134 chiggers and 89 ticks were collected from domestic rodents captured in three counties of Shandong Province. We amplified and sequenced the 56-kDa type-specific antigen gene of O. tsutsugamushi from DNA samples of these Acarina and designated to genotype according to sequence analysis.


RESULTS
Overall, the infestation rate of chiggers on domestic rodents was 17.0%, and the chigger index was 5.38. The infestation rate of ticks on rodents was 3.1%. Natural infection of O. tsutsugamushi was found in Leptotrombidium taishanicum, L. linhuaikongense, L. intermedium, L. scutellare, L. palpale, and Ixodes spp., the minimum positive rates of which were 5.9%, 3.2%, 1.2%, 0.8%, 0.8%, and 2.2%, respectively. Kawasaki-like genotypes were predominant in chiggers and ticks on domestic rodents, which were detected from L. taishanicum, L. intermedium, L. scutellare, L. palpale, and Ixodes spp. Shimokoshi-like genotype was detected from L. palpale.


CONCLUSIONS
In the present study we investigated the infestation of chiggers and ticks on domestic rodents in Shandong Province, and identified the prevalence and genotypes of O. tsutsugamushi in the Acarina. Infestation of vector chiggers in domestic rodents, prevalence of O. tsutsugamushi in infested chiggers, and high nucleotide homologies among the O. tsutsugamushi sequences from the Acarina, their animal hosts and scrub typhus patients, implied that domestic rodents may play an important role in the transmission of scrub typhus in Shandong, China. Further studies are needed to verify the vector significance of chiggers and ticks that tested positive for O. tsutsugamushi, and to assess the risk of human exposure to chiggers and ticks on domestic rodents.
Meng
M
Zhang
Department of Epidemiology and Health Statistics, School of Public Health, Shandong University, Jinan, China. ztzhao@sdu.edu.cn.
Zhong-Tang
ZT
Zhao
Hui-Li
HL
Yang
Ai-Hua
AH
Zhang
Xing-Qu
XQ
Xu
Xiang-Peng
XP
Meng
Hai-Yu
HY
Zhang
Xian-Jun
XJ
Wang
Zhong
Z
Li
Shu-Jun
SJ
Ding
Li
L
Yang
Lu-Yan
LY
Zhang
D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics; D002681:China; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D008924:Mite Infestations / Q000469:parasitology / Q000662:veterinary*; D008969:Molecular Sequence Data; D012285:Orientia tsutsugamushi / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification; D010802:Phylogeny; D012376:Rodent Diseases / Q000469:parasitology; D012377:Rodentia / Q000469:parasitology*; D017422:Sequence Analysis, DNA; D013984:Tick Infestations / Q000469:parasitology / Q000662:veterinary*; D013987:Ticks / Q000382:microbiology*; D014324:Trombiculidae / Q000382:microbiology*
D000942:Antigens, Bacterial; D004269:DNA, Bacterial