The species diversity of ticks that attack human hosts in Eastern Siberia (Russian Federation) and prevalence of tick-borne pathogens

Abstract

Purpose: The purpose of this work was to characterize the population of ticks that attack humans in the Eastern Siberia and analyze the dynamics of tick-borne infections in the region. Methods & Materials: Ticks were delivered to the laboratory by bitten people between 25.03.2007 and 17.10.2017. The developmental stage and species of ticks were identified morphologically using appropriate key guides. Four tick-borne pathogens, i.e. tick-borne encephalitis virus (TBEV), Borrelia burgdorferi sensu lato, Anaplasma phagocytophylum, Ehrlichia muris\E. chaffeensis were detected in ticks using the range of laboratory diagnostic metods, including direct ligth microscopy, ELISA and real-time PCR. Results: Total of 46357 tick specimens detached from bitten people were identified and tested individually during 10 consecutive years. The majority (85,4%) of victims was bitten by I. persulcatus; 14,55% of attacks on humans were caused by D. nuttalli and D. silvarum; whereas H. concinna was documented only in 25 cases (0.05%). Among all studied ticks, several unconventional species i.e. Rhipicephalus sanguineus, D. reticulatus and Amblyomma americanum were identified. In 2017, besides two cases of R. sanguineus bites, the bite of A. testudinarium was registered. Analysis of tick bite histories indicates that five cases have local origin whereas other five ticks are inported from endemic regions. Mean prevalence of infection in I. persulcatus comprised 12 ± 6,5%, 7,8 ± 2,7%, 4,6 ± 1,5% and 1 ± 0,7% for B. burgdorferi sensu lato, A. phagocytophylum, Ehrlichia sp. and TBEV respectively. The dynamics of the prevalence of TBEV and B. burgdorferi s.l. in I. persulcatus indicate the significant increase of infection rate during 2014 – 2017. In Dermacentor sp., the prevalence of every infection was below 5%, with the highest rate for A. phagocytophilum (4,2 ± 3,7%). No pathogens detected in H. concinna. Conclusion: I. persulcatus remains the most important vector of tick-borne diseases to humans in Eastern Siberia with highest attack rate and with about 25% of ticks being infected with at least one of four pathogens. The H. concinna does not play any significant role as a disease vector. The regular events of invasion of non-endmic tick species are discovered.