title: Low risk of seroconversion or clinical disease in humans after a bite by an Anaplasma phagocytophilum-infected tick.
abstract: The risk of contracting human granulocytic anaplasmosis (HGA) after a tick bite is mainly unknown. In this study we investigated the clinical and serological response in 30 humans bitten by ticks positive for Anaplasma phagocytophilum (Group A), 30 humans bitten by Borrelia burgdorferi sensu lato (s.l.)-positive ticks (Group B), and 30 humans bitten by ticks negative for both A. phagocytophilum and B. burgdorferi s.l. (Group C). Ticks, blood samples and questionnaires were collected from tick-bitten humans at 34 primary healthcare centres in Sweden and in the Åland Islands, Finland, at the time of the tick bite and after three months. A total of 2553 ticks detached from humans in 2007-2009 were analyzed by polymerase chain reaction, and 31 (1.2%) were positive for A. phagocytophilum, 556 (21.8%) were positive for B. burgdorferi s.l., and eight (0.3%) were co-infected by A. phagocytophilum and B. burgdorferi s.l. The overall prevalence of Anaplasma IgG antibodies in the included participants (n=90) was 17%, and there was no significant difference between the groups A-C. Only one of the participants (in Group C) showed a four-fold increase of IgG antibodies against A. phagocytophilum at the three-month follow-up, but reported no symptoms. The frequency of reported symptoms did not differ between groups A-C, and was unrelated to the findings of A. phagocytophilum and B. burgdorferi s.l. in the detached ticks. We conclude that the risk for HGA or asymptomatic seroconversion after a tick bite in Sweden or in the Åland Islands is low, even if the tick is infected by A. phagocytophilum.
authors.affiliation: Department of Clinical Microbiology, Ryhov County Hospital, S-551 85 Jönköping, Sweden. Electronic address: anna.jonsson.henningsson@rjl.se.
authors.forename: Anna J
authors.initials: AJ
authors.lastname: Henningsson
authors.affiliation: Division of Medical Microbiology, Department of Clinical and Experimental Medicine, Linköping University, S-581 85 Linköping, Sweden.
authors.forename: Peter
authors.initials: P
authors.lastname: Wilhelmsson
authors.affiliation: Department of Infectious Diseases, Ryhov County Hospital, S-551 85 Jönköping, Sweden.
authors.forename: Paula
authors.initials: P
authors.lastname: Gyllemark
authors.affiliation: Division of Medical Microbiology, Department of Clinical and Experimental Medicine, Linköping University, S-581 85 Linköping, Sweden.
authors.forename: Monika
authors.initials: M
authors.lastname: Kozak
authors.affiliation: Department of Clinical Microbiology, Ryhov County Hospital, S-551 85 Jönköping, Sweden.
authors.forename: Andreas
authors.initials: A
authors.lastname: Matussek
authors.affiliation: The Åland Group for Borrelia Research, Bimelix Biomedical Laboratory, Torggatan 10, AX-22100 Mariehamn, Åland, Finland.
authors.forename: Dag
authors.initials: D
authors.lastname: Nyman
authors.affiliation: Division of Clinical Immunology, Department of Clinical and Experimental Medicine, Linköping University, S-551 85 Jönköping, Sweden.
authors.forename: Christina
authors.initials: C
authors.lastname: Ekerfelt
authors.affiliation: Department of Clinical Microbiology, Ryhov County Hospital, S-551 85 Jönköping, Sweden; Division of Medical Microbiology, Department of Clinical and Experimental Medicine, Linköping University, S-581 85 Linköping, Sweden.
authors.forename: Per-Eric
authors.initials: PE
authors.lastname: Lindgren
authors.affiliation: Clinic of Infectious Diseases, Linköping University Hospital, and Department of Clinical and Experimental Medicine, Linköping University, S-551 85 Jönköping, Sweden.
authors.forename: Pia
authors.initials: P
authors.lastname: Forsberg
mesh_terms: D041081:Anaplasma phagocytophilum / Q000502:physiology*; D015748:Borrelia burgdorferi Group; D016873:Ehrlichiosis / Q000453:epidemiology / Q000209:etiology / Q000382:microbiology / Q000635:transmission*; D006801:Humans; D012307:Risk Factors; D012537:Scandinavian and Nordic Countries / Q000453:epidemiology; D000069078:Seroconversion; D064927:Tick Bites / Q000150:complications*
keywords: Anaplasama phagocytophilum; Anaplasmosis; Ehrlichiosis; Human; Seroconversion; Tick bite