Experiments were conducted to investigate the potential for transmission of Orientia tsutsugamushi, the aetiological agent
for scrub typhus, when naturally infected mite larvae were co-feeding with uninfected larvae. Larvae from colonies of
Leptotrombidium deliense and L. imphalum infected with O. tsutsugamushi were used. Transmission of O. tsutsugamushi to
previously uninfected L. deliense and Blankaartia acuscutellaris co-fed with infected L. deliense was shown to occur. The
overall minimum rate of acquisition was 1·6% (4/258) for L. deliense and 2·5% (3/119) for B. acuscutellaris. When
individual infected L. deliense were co-fed with B. acuscutellaris acquisition of O. tsutsugamushi was not detected. However,
when 4 and 8 infected larvae were co-fed with B. acuscutellaris acquisition of O. tsutsugamushi was detected. Transmission
of O. tsutsugamushi was not observed when uninfected L. deliense were co-fed with infected L. imphalum. This novel
transmission route may explain the occurrence of rickettsiae in genera other than Leptotrombidium spp, which are
considered to be the main vectors of O. tsutsugamushi.