Isolation of a novel Orientia species (O. chuto sp. nov.) from a patient infected in Dubai

Abstract

In July 2006, an Australian tourist returning from Dubai, in the United Arab Emirates (UAE), developed acute scrub typhus. Her signs and symptoms included fever, myalgia, headache, rash, and eschar. Orientia tsutsugamushi serology demonstrated a 4-fold rise in antibody titers in paired serum collections (1:512 to 1:8,192), with the sera reacting strongest against the Gilliam strain antigen. An Orientia species was isolated by the in vitro culture of the patient's acute blood taken prior to antibiotic treatment. The gene sequencing of the 16S rRNA gene (rrs), partial 56-kDa gene, and the full open reading frame 47-kDa gene was performed, and comparisons of this new Orientia sp. isolate to previously characterized strains demonstrated significant sequence diversity. The closest homology to the rrs sequence of the new Orientia sp. isolate was with three strains of O. tsutsugamushi (Ikeda, Kato, and Karp), with a nucleotide sequence similarity of 98.5%. The closest homology to the 47-kDa gene sequence was with O. tsutsugamushi strain Gilliam, with a nucleotide similarity of 82.3%, while the closest homology to the 56-kDa gene sequence was with O. tsutsugamushi strain TA686, with a nucleotide similarity of 53.1%. The molecular divergence and geographically unique origin lead us to believe that this organism should be considered a novel species. Therefore, we have proposed the name "Orientia chuto," and the prototype strain of this species is strain Dubai, named after the location in which the patient was infected.

FIG. 1.

Eschar on the abdomen of the patient.

FIG. 2.

Scrub typhus serology showing a marked change in antibody titers when tested against three strains of O. tsutsugamushi during a 56-day period.

FIG. 3.

Phylogenetic tree showing the 16S rRNA gene of Orientia chuto strain Dubai among O. tsutsugamushi strains. The tree was prepared using the neighbor-joining algorithm within the Mega 4 software. Bootstrap values are indicated at each node. The scale bar represents a 0.2% nucleotide divergence.

FIG. 4.

Phylogenetic tree showing the 47-kDa gene of Orientia chuto strain Dubai among O. tsutsugamushi strains. The tree was prepared using the neighbor-joining algorithm within the Mega 4 software. Bootstrap values are indicated at each node. The scale bar represents a 2.0% nucleotide divergence.

FIG. 5.

Phylogenetic tree showing the 56-kDa gene of Orientia chuto strain Dubai among O. tsutsugamushi strains. The tree was prepared using the neighbor-joining algorithm within the Mega 4 software. Bootstrap values are indicated at each node. The scale bar represents a 5.0% nucleotide divergence.

FIG. 6.

Regional map showing the distribution of scrub typhus and the location of Dubai within the UAE. (Modified from a map by Lokal Profil that is freely available on Wikipedia.)