Investigation of Orientia tsutsugamushi infection in rodents and human in Yunnan

Objective To investigate the natural infection of Orientia tsutsugamushi (Ot) in rodents and human' in some areas of Yunnan province. Methods Rat clip and cage traps were used to capture rodents. The spleens of the captured mice and blood samples from patients with fever of unknown origin were collected. DNAs were extracted from mice spleens and blood samples of patients, Ot sta56 segment were amplified by using nested-polymerase chain reaction (nPCR), sequenced to analyze the homology with other known sequences. Results A total of 485 rodents from 7 genera in 11 species were captured, and 23 blood samples of patients were collected for Ot sta56 segment detection with nPCR, the positive rates were 0.41% and 4.35% for rodent spleen samples (HHSP65 and HHSP112) and blood samples of patients (DLRX9) respectively. Compared with sta56 gene sequences of other known Ot strains from GenBank, HHSP65 strain shared 100% homology with HHSP112 strain, and they shared 89.6% homology with TT0711a strains and 79.7% homology with Japan Kawasaki strain. DLRX9 strain shared 81.9% homology with Karp strain, 98.4% homology with PG9 and Li3b strains from Thailand and Jin/2012 strains from Zhejiang of China and 64.8% homology with HHSP65. Phylogenetic analysis showed that HHSP65 strain and TT0711a strains were in different branches, and DLRX9, PG9, Li3b and Jin/2012 stains were in same branch. Conclusion It was confirmed that the Ots causing scrub typhus in some areas of Yunnan province were Karp type Ot and new genotype Ot, which might be related to Japan Kawasaki type.