Abstract
BackgroundAlmost 3500 tick samples, originally collected via a nationwide citizen science campaign in 2015, were screened to reveal the prevalence and distribution of a wide spectrum of established and putative tick-borne pathogens vectored by Ixodes ricinus and I. persulcatus in Finland. The unique geographical distribution of these two tick species in Finland allowed us to compare pathogen occurrence between an I. ricinus-dominated area (southern Finland), an I. persulcatus-dominated area (northern Finland), and a sympatric area (central Finland).ResultsOf the analysed ticks, almost 30% carried at least one pathogen and 2% carried more than one pathogen. A higher overall prevalence of tick-borne pathogens was observed in I. ricinus than in I. persulcatus: 30.0% (604/2014) versus 24.0% (348/1451), respectively. In addition, I. ricinus were more frequently co-infected than I. persulcatus: 2.4% (49/2014) versus 0.8% (12/1451), respectively. Causative agents of Lyme borreliosis, i.e. bacterial genospecies in Borrelia burgdorferi (sensu lato) group, were the most prevalent pathogens (overall 17%). “Candidatus Rickettsia tarasevichiae” was found for the first time in I. ricinus ticks and in Finnish ticks in general. Moreover, Babesia divergens, B. venatorum and “Candidatus Neoehrlichia mikurensis” were reported for the first time from the Finnish mainland.ConclusionsThe present study provides valuable information on the prevalence and geographical distribution of various tick-borne pathogens in I. ricinus and I. persulcatus ticks in Finland. Moreover, this comprehensive subset of ticks revealed the presence of rare and potentially dangerous pathogens. The highest prevalence of infected ticks was in the I. ricinus-dominated area in southern Finland, while the prevalence was essentially equal in sympatric and I. persulcatus-dominated areas. However, the highest infection rates for both species were in areas of their dominance, either in south or north Finland.
Highlights
Almost 3500 tick samples, originally collected via a nationwide citizen science campaign in 2015, were screened to reveal the prevalence and distribution of a wide spectrum of established and putative tick-borne pathogens vectored by Ixodes ricinus and I. persulcatus in Finland
The generalized estimating equation (GEE) model conducted for the adult samples indicated significantly higher probability of finding infected I. ricinus [estimated marginal mean was 0.31 (0.27–0.34)] than I. persulcatus [0.25 (0.22–0.29)] (Wald statistics, χ2 = 4.75, df = 1, P = 0.029)
Pathogen prevalence in parapatric and sympatric areas The highest prevalence of infected ticks was observed in the I. ricinus-dominated area in southern Finland (32.6%), and the lowest prevalence in the sympatric area in central Finland (25.4%)
Summary
Almost 3500 tick samples, originally collected via a nationwide citizen science campaign in 2015, were screened to reveal the prevalence and distribution of a wide spectrum of established and putative tick-borne pathogens vectored by Ixodes ricinus and I. persulcatus in Finland. Studies have shown that I. ricinus and I. persulcatus are potential vectors for many microorganisms in addition to B. burgdorferi (s.l.) [6, 7] These include TBE-virus (TBEV) causing tick-borne encephalitis (TBE), Anaplasma phagocytophilum causing human granulocytic anaplasmosis (HGA) and tick-borne fever (TBF) [8, 9], species of the bacterial genus Rickettsia causing spotted fever and typhus [10], B. miyamotoi spirochete causing hard tick-borne relapsing fever [11], “Candidatus Neoehrlichia mikurensis” causing neoehrlichiosis [12], Babesia protozoans causing babesiosis in animals and humans [13], Francisella tularensis causing tularemia [14] and Bartonella henselae causing cat scratch disease, even though transmission of B. henselae by ticks has not been established [15, 16]. Regarding Bartonella henselae and F. tularensis, no ticks infected by these pathogens have been found in Finland
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