Phylogenetic analysis of tick-borne encephalitis virus strains found in an engorged tick and traveler returning from Russia.

ABSTRACT

Although travel-related tick-borne encephalitis (TBE) cases have been increasingly registered worldwide, very few published case studies are available to date. The present report describes a travel-related TBE case and provides genotypic characterization of two viral isolates. Laboratory diagnostics were based on complement fixation test and virus isolation. This report is unique because the TBE case was first confirmed by virus isolation from the engorged tick and only later from the patient's blood. Moreover, this case demonstrated a successful prophylaxis performed on day 8 post tick exposure although it is generally recommended that anti-TBEV immunoglobulins should be administered not later than on day 4 after tick bite. Sequences of E protein gene fragments were used to phylogenetically characterize the two isolates. The results demonstrated that both viral isolates belonged to clusteron 3A (Zausaev group) of the Asian lineage of the TBEV Siberian subtype. The synonymous nucleotide substitution, C351 T, was identified in E protein gene fragments of TBEV 88 and TBEV 89, which could have been induced by virus transmission. A few important take-home messages can be gleaned from the reported case. First, travelers should be aware of TBE endemic areas that they plan to visit and be proactive when exposed to Ixodes ticks. Second, medical practitioners should always consider travel history and potential tick exposure of patients. Lastly, engorged Ixodes spp. ticks removed from the patients, who have arrived from endemic areas, should be tested for TBEV even in the absence of TBE clinical signs.