Epidemiological features of scrub typhus and molecular characteristics of Orientia tsutsugamushi in north-central Bangladesh.

OBJECTIVES

Scrub typhus is an acute febrile disease caused by Orientia tsutsugamushi transmitted through trombiculid mites. This study aimed to clarify the prevalence and clinical features of scrub typhus and the molecular epidemiological characteristics of O. tsutsugamushi in north-central Bangladesh.

METHODS

Blood samples were collected from patients with febrile illness at a single medical institution over a 1-year period. Using DNA samples extracted from blood, O. tsutsugamushi was identified by nested polymerase chain reaction targeting the outer membrane protein (47-kDa) gene. Phylogenetic analysis was performed based on the genes encoding a 56-kDa type-specific antigen (TSA) and trxA, along with genotyping by multilocus sequence typing (MLST).

RESULTS

Among the 744 patients, 72 (9.7%) were diagnosed with the scrub typhus and exhibited nausea (93%) and myalgia (75%) more commonly than did non-scrub typhus cases. On the basis of the TSA gene, eight samples were assigned to Karp-related (n = 7; clades 2 and 4b) and Gilliam (n = 1) genotypes. Among the 10 samples, nine sequence types (STs), including eight new types (ST101-ST108) were identified, with three STs grouped into clonal complex 105 (CC105). On the basis of the phylogenetic analysis of trxA, the Bangladeshi samples were differentiated into two clusters.

CONCLUSIONS

The genetic characteristics of O. tsutsugamushi in Bangladesh revealed a potentially dominant genetic group (Karp-c2 and CC105).