Transmission of Orientia tsutsugamushi, the aetiological agent for scrub typhus, to co-feeding mites

Abstract

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.

Variable clinical responses of a scrub typhus outbred mouse model to feeding by Orientia tsutsugamushi infected mites

“…We determined that feeding by a single infected chigger produced similar clinical responses in laboratory mice than pool feeding for two of the three mite species; only among Lc lines differences between IF and PF were significant. In a previous study, the average antibody titer was found to be lower after Ld individual feeding than after pool feeding, and one mouse died from the pool feeding procedure (Frances et al 2000b). Unfortunately we did not determine antibody titers in our study.…”

“…Rat is generally larger than mouse; therefore their immune system and disease resistance may be different. Wild rodents might get infected with scrub typhus more than once so the scrub typhus disease may persist (Frances et al 2000b). Laboratory ICR mice have never been infected with scrub typhus so a higher mortality rate can be expected than for wild rodents.…”

Orientia tsutsugamushi, agent of scrub typhus, displays a single metapopulation with maintenance of ancestral haplotypes throughout continental South East Asia

“…Horizontal transmission was demonstrated on naïve chigger feeding on previously infected rodents (Traub et al, 1975). It was also reported to occur between mites co-feeding on infected rodents (Frances et al, 2000). Chigger mites thus infect their host with the strain they bear and could also become infected with O. tsutsugamushi strains infecting previously this same host (Takahashi et al, 1990).…”

Occurrence of Orientia Tsutsugamushi in Small Mammals From Thailand

“…Although studies by Traub and others, 12 Walker and others, 8 Takahashi and others, 11 and Frances and others 10 have demonstrated that chiggers can acquire O. tsutsugamushi during the feeding process, to date mammals have not been shown to play a conclusive role in the cyclical transmission of this pathogen. 13 In spite of this, rodents play a key role in the epidemiology of scrub typhus, as rodents serve as maintenance hosts for the vector mites.…”

“…8,9 Infected chiggers can therefore be considered the true hosts of O. tsutsugamushi, and even commonly infected mammals are dead-end hosts rather than true reservoirs. Frances and others 10 demonstrated that O. tsutsugamushi could be transmitted to co-feeding mites, and Takahashi and others 11 were able to infect chiggers fed on wild rodents; however, neither study determined if infected mites transmitted the rickettsiae to their eggs. Traub and others 12 were the first to document horizontal transmission of O. tsustsugamushi, although even this report discussed the possibility that the observation was not representative of natural transmission.…”