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Prevalence of Rickettsia spp. in Ticks and Serological and Clinical Outcomes in Tick-Bitten Individuals in Sweden and on the Åland Islands
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Infectious Diseases. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Medicinska och farmaceutiska vetenskapsområdet, centrumbildningar mm, Center for Clinical Research Dalarna.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Microbiology and Infectious Medicine, Clinical Bacteriology.
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2016 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 11, e0166653Article in journal (Refereed) Published
Abstract [en]

Tick-transmitted diseases are an emerging health problem, and the hard tick Ixodes ricinus is the main vector for Borrelia spp., tick-borne encephalitis virus and most of the spotted fever Rickettsiae in Europe. The aim of the present study was to examine the incidence of rickettsial infection in the southernmost and south central parts of Sweden and the Aland Islands in Finland the risk of infection in humans and its correlation with a bite of a Rickettsia-infected tick, the self-reported symptoms of rickettsial disease, and the prevalence of co-infection between Rickettsia spp. and Borrelia spp. Persons with a recent tick bite were enrolled through public media and asked to answer a questionnaire, provide a blood sample and bring detached ticks at enlistment and at follow-up three months later. Blood samples were previously analysed for Borrelia spp. antibodies and, for this report, analysed for antibodies to Rickettsia spp. by immunofluorescence and in 16 cases also using Western Blot. Ninety-six (44.0%) of the 218 participants were seropositive for IgG antibodies to Rickettsia spp. Forty (18.3%) of the seropositive participants had increased titres at the follow-up, indicating recent/current infection, while four (1.8%) had titres indicating probable recent/current infection (>= 1: 256). Of 472 ticks, 39 (8.3%) were Rickettsia sp. positive. Five (31.3%) of 16 participants bitten by a Rickettsia-infected tick seroconverted. Experience of the selfreported symptoms nausea (p = 0.006) and radiating pain (p = 0.041) was more common among those with recent, current or probable infection compared to those who did not seroconvert. Participants who showed seroreactivity or seroconversion to Rickettsia spp. had more symptoms than those who were seronegative. Seven (3.2%) participants showed seroconversion to Borrelia spp., and three (1.4%) of these showed seroconversion to both Rickettsia spp. and Borrelia spp., in accordance with previous studies in Sweden. Symptoms of rickettsial disease were in most of the cases vague and general that were difficult to differentiate from other tick-borne diseases.

Place, publisher, year, edition, pages
2016. Vol. 11, no 11, e0166653
National Category
Infectious Medicine
Research subject
Infectious Diseases
Identifiers
URN: urn:nbn:se:uu:diva-298936DOI: 10.1371/journal.pone.0166653ISI: 000387794600098OAI: oai:DiVA.org:uu-298936DiVA: diva2:948484
Available from: 2016-07-12 Created: 2016-07-12 Last updated: 2017-02-01Bibliographically approved
In thesis
1. Spotted Fever Rickettsioses in Sweden: Aspects of Epidemiology, Clinical Manifestations and Co-infections
Open this publication in new window or tab >>Spotted Fever Rickettsioses in Sweden: Aspects of Epidemiology, Clinical Manifestations and Co-infections
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The spotted fever group rickettsiae are emerging diseases. They cause damage in their hosts by invading the endothelium in small to medium-sized blood vessels, which results in vasculitis that can cause clinical manifestations from most organs.

The present thesis describes the prevalence of Rickettsia helvetica in ticks, the incidence of rickettsial infection based on seroreactivity and seroconversion in humans and their symptoms, from different parts of Sweden and the Åland Islands in Finland. This was accomplished through serological analysis of both retrospective and prospective serum samples from confirmed and suspected tick-bitten individuals compared to individuals with no knowledge of tick exposure (blood donors). We found a comparable seroprevalence to Rickettsia spp. in different geographical areas where ticks are present; it was also comparable to the seroprevalence of Borrelia spp. Seroprevalence was also more common, as suspected, in the tick-exposed group compared to blood donors. In comparison with co-infections with other tick-borne infections (Anaplasma spp. and Borrelia spp.), we could conclude that co-infections do exist and that, based on clinical findings, it is difficult to distinguish which microorganism causes certain clinical manifestations. For reliable conclusions regarding the causative microorganism, the diagnosis should basically rely on diagnostic tests. In comparison with Borrelia spp., seroconversion to Rickettisa spp. was more common in the areas we investigated, indicating that rickettsiosis is a common tick-borne infection in Sweden and most likely underdiagnosed.

When investigating patients with meningitis, we found R. felis in cerebrospinal fluid from two patients with subacute meningitis. This was the first report in which R. felis was found and diagnosed in patients in Sweden. The patients recovered without sequelae and without causal treatment. To provide guidelines on when to treat Rickettisa spp. infections, more investigations are needed.

The present thesis shows that Rickettsia spp. are common in ticks and do infect humans. Rickettsial infection should be considered in both non-specific or specific symptoms after a tick bite. It was also shown in the thesis that flea-borne rickettsiosis (R. felis) occurs in Sweden and may cause invasive infections

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1253
Keyword
Rickettsia helvetica, Rickettsia felis, co-infection, erythema migrans, meningitis, serology, PCR, western blot
National Category
Infectious Medicine
Research subject
Infectious Diseases
Identifiers
urn:nbn:se:uu:diva-302137 (URN)978-91-554-9677-7 (ISBN)
Public defence
2016-10-26, Mikrobiologens hörsal, Dag Hammarskjöldsväg 17, Uppsala, 13:15 (Swedish)
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Supervisors
Available from: 2016-10-03 Created: 2016-08-30 Last updated: 2016-10-11

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