Scrub typhus: vector competence of Leptotrombidium chiangraiensis chiggers and transmission efficacy and isolation of Orientia tsutsugamushi.

A total of 4,281 rodents, belonging to 20 species, was collected from three villages in Chiangrai Province, northern Thailand, from January 1994 to December 2001. The predominant species were Rattus rattus, R. losea and Bandicota indica, accounting for 96% of the total. More than 135,000 chigger mites were removed from wild rodents of which 1% were identified as Leptotrombidium chiangraiensis, a new species vector of scrub typhus. Five Orientia tsutsugamushi-infected L. chiangraiensis colonies established from chiggers removed from R. rattus and R. losea rodents. The prevalence of O. tsutsugamushi infection in colonies ranged from 7-89%. Vertical and horizontal transmission efficacies of O. tsutsugamushi were stable between generations among colonies of L. chiangraiensis. The two isolates of O. tsutsugamushi obtained from individual adult L. chiangraiensis mites represent the first successful isolation of this bacterium from individual adult mites. Characterization of the O. tsutsugamushi isolates is under way.

Short report: Thai tick typhus, Rickettsia honei, and a unique rickettsia detected in Ixodes granulatus (Ixodidae: Acari) from Thailand.

A unique Rickettsia species (Rickettsia thailandii sp. nov.) was identified in an Ixodes granulatus by use of polymerase chain reaction heteroduplex mobility assay by use of segments of the citrate synthase gene. This tick was collected from Rattus rattus from Nakhon Ratchasima province in 1970. Another I. granulatus was infected with Thai tick typhus strain TT-118, Rickettsia honei sp. nov. Stenos, Roux, Walker & Raoult; this tick was removed from a R. rattus collected 4 years later from the same province. Ixodes granulatus is the first tick species in Australasia shown to be infected with R. honei and the unique Rickettsia species.