title: Tick-borne encephalitis virus in ticks detached from humans and follow-up of serological and clinical response.
abstract: The risk of tick-borne encephalitis virus (TBEV) infection after a tick bite remains largely unknown. To address this, we investigated the presence of TBEV in ticks detached from humans in an attempt to relate viral copy number, TBEV subtype, and tick feeding time with the serological and clinical response of the tick-bitten participants. Ticks, blood samples, and questionnaires were collected from tick-bitten humans at 34 primary health care centers in Sweden and in the Åland Islands (Finland). A total of 2167 ticks was received from 1886 persons in 2008-2009. Using a multiplex quantitative real-time PCR, 5 TBEV-infected ticks were found (overall prevalence 0.23%, copy range <4×10(2)-7.7×10(6)per tick). One unvaccinated person bitten by a tick containing 7.7×10(6) TBEV copies experienced symptoms. Another unvaccinated person bitten by a tick containing 1.8×10(3) TBEV copies developed neither symptoms nor TBEV antibodies. The remaining 3 persons were protected by vaccination. In contrast, despite lack of TBEV in the detached ticks, 2 persons developed antibodies against TBEV, one of whom reported symptoms. Overall, a low risk of TBEV infection was observed, and too few persons got bitten by TBEV-infected ticks to draw certain conclusions regarding the clinical outcome in relation to the duration of the blood meal and virus copy number. However, this study indicates that an antibody response may develop without clinical symptoms, that a bite by an infected tick not always leads to an antibody response or clinical symptoms, and a possible correlation between virus load and tick feeding time.
authors.affiliation: Division of Medical Microbiology, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden. Electronic address: Pontus.lindblom@liu.se.
authors.forename: Pontus
authors.initials: P
authors.lastname: Lindblom
authors.forename: Peter
authors.initials: P
authors.lastname: Wilhelmsson
authors.forename: Linda
authors.initials: L
authors.lastname: Fryland
authors.forename: Johanna
authors.initials: J
authors.lastname: Sjöwall
authors.forename: Mats
authors.initials: M
authors.lastname: Haglund
authors.forename: Andreas
authors.initials: A
authors.lastname: Matussek
authors.forename: Jan
authors.initials: J
authors.lastname: Ernerudh
authors.forename: Sirkka
authors.initials: S
authors.lastname: Vene
authors.forename: Dag
authors.initials: D
authors.lastname: Nyman
authors.forename: Ashild
authors.initials: A
authors.lastname: Andreassen
authors.forename: Pia
authors.initials: P
authors.lastname: Forsberg
authors.forename: Per-Eric
authors.initials: PE
authors.lastname: Lindgren
mesh_terms: D000818:Animals; D001096:Arachnid Vectors / Q000821:virology*; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004669:Encephalitis Viruses, Tick-Borne / Q000302:isolation & purification*; D004675:Encephalitis, Tick-Borne / Q000453:epidemiology / Q000635:transmission* / Q000821:virology; D005260:Female; D005500:Follow-Up Studies; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D018884:Ixodes / Q000821:virology*; D007814:Larva; D008297:Male; D008969:Molecular Sequence Data; D009758:Nymph; D010802:Phylogeny; D012367:RNA, Viral / Q000235:genetics; D012306:Risk; D017422:Sequence Analysis, DNA; D013548:Sweden / Q000453:epidemiology; D064927:Tick Bites
chemical_list: D017931:DNA Primers; D012367:RNA, Viral
keywords: Clinical symptoms; Ixodes ricinus; Real-time PCR; Serology; TBEV