Co-infections with multiple pathogens in natural populations of Ixodes persulcatus ticks in Mongolia.

Background: In Mongolia, the taiga tick Ixodes persulcatus is the major vector of tick-borne pathogens. Knowledge about co-infections of these pathogens in ticks is necessary both for understanding their persistence in nature and for diagnosing and treating tick-borne diseases.

Methods: The prevalence of seven tick-borne infections in 346 I. persulcatus collected from the Selenge and Bulgan provinces of Mongolia was evaluated using real-time PCR. Quantification of Borrelia spp. was performed using multiplex quantitative PCR targeting the 16S rRNA gene. Genetic analysis of Borrelia spp. in 11 ticks infected with Borrelia miyamotoi, including six ticks co-infected with Borrelia burgdorferi sensu lato (s.l.), was performed by high-throughput sequencing of the flaB gene fragment.

Results: Six ticks (1.7%) were infected with tick-borne encephalitis virus (TBEV); 171 (49.4%), with B. burgdorferi sensu lato; 17 (4.9%), with B. miyamotoi; 47 (13.6%), with Anaplasma phagocytophilum; and 56 (16.2%), with Ehrlichia sp. Neither Rickettsia sibirica nor R. heilongjiangensis were detected. Borrelia burgdorferi s.l. occurred as co-infection in 55 (32.2%) of all infected ticks. The other pathogens co-infected ticks in 58.8-70.2% of cases. No pairwise associations between co-infecting pathogens were observed, with the exception of a positive association between A. phagocytophilum and Ehrlichia sp.

Infections: The spirochete loads of B. miyamotoi were significantly higher than those of B. burgdorferi s.l. (mean: 5.2 vs 4.0 log10 genome copies/tick, respectively). Ten isolates of B. miyamotoi belonged to the Siberian lineage. Borrelia burgdorferi s.l was represented by nine isolates of B. afzelii, B. bavariensis and B. garinii.

Conclusions: In populations of I. persulcatus inhabiting the Selenge and Bulgan provinces of Mongolia, five vector-borne pathogens, i.e. TBEV, B. burgdorferi s.l., B. miyamotoi, A. phagocytophilum and Ehrlichia sp., persist independently from each other, with the exception of A. phagocytophilum and Ehrlichia sp. which seem to share the circulation mode. The discrepancies in B. burgdorferi s.l. and B. miyamotoi prevalence and spirochete load per tick suggest that different ecological niches are occupied by Lyme disease and relapsing fever agents. High-throughput sequencing allows genetic identification of borreliae species in co-infected ticks.