Scrub Typhus: No Longer Restricted to the Tsutsugamushi Triangle

Abstract

Scrub typhus is the most important rickettsial disease in the world. Its previous endemic region was considered to be in Asia, Australia and islands in the Indian and Pacific Oceans; this area was referred to as the Tsutsugamushi Triangle. Accumulation of serological, molecular, genetic, and culture data have shown that not only is scrub typhus not limited to the Tsutsugamushi Triangle, but can be caused by orientiae other than Orientia tsutsugamushi. This review describes evidence currently available that will be instrumental to researchers, healthcare providers and medical leaders in developing new research projects, performing diagnosis, and preventing scrub typhus in locations not previously thought to be endemic.

Keywords: Orientia tsutsugamushi; Tsutsugamushi Triangle; endemic region; scrub typhus.

Figure 1

Evolutionary relationships of Orientia species (in bold) detected outside of the Tsutsugamushi Triangle compared with Orientia tsutsugamushi strains and Rickettsia species (GenBank accession numbers are shown next to each agent). The tree was based on 256 bp rrs gene fragments and constructed using the Maximum Likelihood method based on the Tamura-Nei model. Evolutionary analyses were conducted in MEGA7 and the values for the bootstrap test (1000 replicates) are shown next to the branches. The tree is drawn to scale, with branch lengths measured by the number of substitutions per site.

Figure 2

Human and animal serological and molecular evidence of Orientia spp. infections in new endemic regions of scrub typhus outside of the Tsutsugamushi Triangle (shown in brown).