Biological and Genetic Characterization of Rickettsia sibirica Strains Isolated in the Endemic Area of the North Asian Tick Typhus

Abstract

Restriction fragment length polymorphism (RFLP) analysis of polymerase chain reaction-amplified gene fragments was used to characterize 24 isolates of spotted fever group rickettsiae previously identified as Rickettsia sibirica from their serologic properties. These strains were obtained in Russia between 1946 and 1991 from humans and different species of Ixodid ticks. The RFLP analysis was performed using amplified DNA products obtained with a genus-specific primer pair derived from the R. prowazekii citrate synthase gene and two group-specific primer pairs from the R. rickettsii 190-kD and 120-kD surface protein antigen genes followed by Alu I, Pst I, and Rsa I restriction endonuclease digestions. Although some differences were detected in biological characteristics among the examined strains, only a single R. sibirica genotype was found with these molecular tools of identification.

Tick-Borne Rickettsioses around the World: Emerging Diseases Challenging Old Concepts

“…sibirica has been found in several species of ticks, and some of them have been presented as the principal vectors Siberian tick typhus (297). These include Dermacentor nuttalli in the mountainous steppe of western and eastern Siberia, D. marginatus in the steppe and meadow regions of western Siberia and northern Kazakhstan, Dermacentor silvarum in forest shrubs, and Haemaphysalis concinna in swampy tussocks of some southern and far eastern territories of Siberia (17,297). Isolates obtained from these species of ticks, respectively, in 1949, 1959, 1983, and 1986 are available at the Gamaleya Research Institute of Epidemiology and Microbiology in Moscow (17).…”

“…These include Dermacentor nuttalli in the mountainous steppe of western and eastern Siberia, D. marginatus in the steppe and meadow regions of western Siberia and northern Kazakhstan, Dermacentor silvarum in forest shrubs, and Haemaphysalis concinna in swampy tussocks of some southern and far eastern territories of Siberia (17,297). Isolates obtained from these species of ticks, respectively, in 1949, 1959, 1983, and 1986 are available at the Gamaleya Research Institute of Epidemiology and Microbiology in Moscow (17). These ticks may act as vectors but also reservoirs of R. sibirica which is maintained in ticks through transstadial and transovarial transmission, as demonstrated at least for D. nuttalli.…”

“…R. sibirica is the agent of Siberian tick typhus, a spotted fever group rickettsiosis that was first described in Primorye in the spring-summer season of 1934 to 1935 by Shmatikov (280). Human isolates obtained in 1946 were used as reference strains for molecular studies many years later (17). Siberian tick typhus is well documented in the former USSR, but relatively few descriptions are available in the English medical literature (280).…”

Quantitative Analyses of Variations in the Injury of Endothelial Cells Elicited by 11 Isolates ofRickettsia rickettsii

“…It is possible that the isolates of R. rickettsii which exhibit different virulence for guinea pigs differ primarily because they were isolated during different phases of a normal cycle of adaptation to their vertebrate and invertebrate hosts that is characteristic of the species. R. sibirica also has a complex cycle of maintenance in nature and distinct biotypes that differ in virulence for guinea pigs (6). Characterization of the changes in rickettsial gene expression that may occur immediately after tick-to-human or tick-to-animal transitions may require development of more complex experimental systems.…”

Isolation of Rickettsia helvetica from ticks in Slovakia

“…helvetica (Burgdorfer et al, 1979), R. slovaca (Brezina et al, 1969), R. sibirica (Balayeva et al, 1996), and R. raoultii (Mediannikov et al, 2008) are the most prevalent rickettsial species frequently detected in central and eastern europe. (Beati et al, 1993) was first time isolated from I. ricinus ticks in Switzerland (Burgdorfer et al, 1979) and later on confirmed all around the old continent.…”