Enhanced threat of tick-borne infections within cities? Assessing public health risks due to ticks in urban green spaces in Helsinki, Finland

Most tick-related studies in Europe have been conducted in nonurban areas, but ticks and tick-borne pathogens also occur in urban green spaces. From a public health perspective, risks regarding tick-borne infections should be studied in these urban areas, where contacts between infected ticks and humans may be more frequent than elsewhere, due to high human activity. We examined the risk of encountering an infected tick in urban green spaces in Helsinki, Finland. We collected ticks at nine sites throughout Helsinki, recorded the prevalence of several pathogens and identified areas with a high potential for contacts between infected ticks and humans. Moreover, we explored the relationship between the density ofBorrelia burgdorferisensu lato-infected ticks and locally diagnosed cases of borreliosis and compared the potential for human-tick encounters in Helsinki to those in nonurban areas in south-western Finland. During 34.8 km of cloth dragging, 2,417Ixodes ricinuswere caught (402 adults, 1,399 nymphs and 616 larvae). From analysed nymphs, we found 11 distinct tick-borne pathogens, with 31.5% of nymphs carrying at least one pathogen. Tick activity was highest in August and September, leading to the density of nymphs infected withB. burgdorferis.l., and concurrently infection risk, to also be highest during this time. Nymph densities varied between the sampling sites, with obvious implications to spatial variation in infection risk. While ticks and tick-borne pathogens were found in both Helsinki and nonurban areas in south-western Finland, the estimates of human activity were generally higher in urban green spaces, leading to a higher potential for human-tick contacts therein. The presence of ticks and tick-borne pathogens and high local human activity in urban green spaces suggest that they form potential foci regarding the acquisition of tick-borne infections. Risk areas within cities should be identified and knowledge regarding urban ticks increased.peerReviewe

Absence of Francisella tularensis in Finnish Ixodes ricinus and Ixodes persulcatus ticks

Francisella tularensis subsp. holarctica is the causative agent of tularaemia in Europe. Finland is a high-incidence region for tularaemia, with mosquito bites as the most common sources of infection. However, in Central and Western Europe, ticks (Acari: Ixodidae) have been suggested as the main vectors. Indeed, several studies have reported the pathogen from the locally most common human-biting tick species, Ixodes ricinus. In Finland, the occurrence of the pathogen in ticks has started receiving attention only recently. Here, we collate previous tick screening data from Finland regarding F. tularensis as well as present the results from a novel screening of roughly 15 000 I. ricinus and I. persulcatus collected from across the country. In total, 14 878 ticks collected between 2015 and 2020 were screened for F. tularensis using a TaqMan-based qPCR assay targeting the 23 KDa gene. The combined screening efforts of the current and previous studies, encompassing roughly 20 000 ticks, did not find any positive ticks. Given the negative results despite the considerable sample size, it appears that the pathogen is not circulating in local tick populations in Finland. We discuss some possible reasons for the lack of the bacterium in ticks in this high-incidence region of tularaemia

First evidence of Ixodiphagus hookeri (Hymenoptera: Encyrtidae) parasitization in Finnish castor bean ticks (Ixodes ricinus)

Ixodiphagus hookeri (Hymenoptera: Encyrtidae) is a parasitoid wasp specialized in parasitizing the larvae and nymphs of ticks (Acari: Ixodidae). As parasitized ticks die prior to reproduction, I. hookeri is seen as a prime biological control agent candidate. Despite this, little is known of their occurrence or ecology in northern Europe. The main aim of the current study was to determine whether adult wasps or parasitized ticks can be found from a tick-infested island in southwestern Finland, using field collections and molecular methods. Following the initial discovery of an adult I. hookeri female on Seili Island, we set out to collect further specimens via sweep netting and Malaise trappings between May and October 2017. Furthermore, 1310 Ixodes ricinus (1220 nymphs, 90 adults) collected from the island during 2012–2014 were screened for I. hookeri DNA using qPCR. Whereas no further wasp specimens could be collected via sweep netting or Malaise trappings, I. hookeri DNA was consistently detected in I. ricinus nymphs (annual minimum infection rates in 2012, 2013, and 2014: 2.3, 0.4, and 0.5%, respectively), whereas all adult samples were negative. Although the annually repeated detections of parasitized ticks suggest that the wasp inhabits the island, further field and molecular surveys are needed to more comprehensively determine the status and stability of the population.</p

Crowdsourcing-based nationwide tick collection reveals the distribution of Ixodes ricinus and I. persulcatus and associated pathogens in Finland

A national crowdsourcing-based tick collection campaign was organized in 2015 with the objective of producing novel data on tick distribution and tick-borne pathogens in Finland. Nearly 20 000 Ixodes ticks were collected. The collected material revealed the nationwide distribution of I. persulcatus for the first time and a shift northwards in the distribution of I. ricinus in Finland. A subset of 2038 tick samples containing both species was screened for Borrelia burgdorferi sensu lato (the prevalence was 14.2% for I. ricinus and 19.8% for I. persulcatus), B. miyamotoi (0.2% and 0.4%, respectively) and tick-borne encephalitis virus (TBEV; 0.2% and 3.0%, respectively). We also report new risk areas for TBEV in Finland and, for the first time, the presence of B. miyamotoi in ticks from mainland Finland. Most importantly, our study demonstrates the overwhelming power of citizen science in accomplishing a collection effort that would have been impossible with the scientific community alone.Peer reviewe

Tick distribution and tick-borne pathogens in Finland - The tick project of the University of Turku

Ticks and tick-borne diseases are a growing problem in northern Europe and Russia. Surveys conducted in Russia, Sweden and Norway have revealed a northwards shift in distribution and an increase in tick abundance over the past few decades. However, despite ticks being actively studied in neighboring countries, ecological data of Finnish tick populations are almost non-existent. Furthermore, the last nationwide mapping of the geographical distribution of Ixodes ricinus in Finland is over five decades old. Regarding the distribution of the taiga tick (Ixodes persulcatus), no nationwide surveys have ever been made. The University of Turku tick project was started in 2012 with the objective of producing novel data on tick abundance, ecology and tick-borne pathogen diversity in Finland. Initially the main aim of the project was to revisit several study locations around Southwest Finland from where previous ecological and Borrelia burgdorferi sensu lato prevalence data was available. Blanket dragging was conducted at these locations, to survey possible changes in tick abundance and B. burgdorferi s.l. prevalence. Additional blanket dragging locations were added around southwestern Finland later in 2013-2014. In addition to B. burgdorferi s.l., the occurrence and prevalence of several other tick-borne pathogens has also been determined from these samples. Furthermore, a long-term surveillance site for tracking annual changes in tick abundance, seasonal questing activity patterns and pathogen diversity was established in 2012 on one of the study locations, Seili. Similar surveillance sites were established in 2015 at several university research stations all around Finland. However, in addition to these local data of tick abundance, activity patterns and pathogen diversity, the project also wanted to produce nationwide data on the geographical distribution of the two currently known disease-transmitting tick species in Finland, I. ricinus and I. persulcatus. To accomplish this, we decided to try a crowdsourcing approach: in 2014 we launched a national questionnaire survey on the internet, asking citizens to report their tick sightings via coordinates. We received nearly 4400 answers to the questionnaire and subsequently released a map visualizing the coordinate points given in those answers (www.puutiaiset.fi). Inspired by the success of this questionnaire, we organized a national tick collection campaign in 2015, where we asked citizens to send ticks to us at the University of Turku. The collection campaign was a success, with nearly 7000 letters delivered to the university. These letters contained approximately 20 000 individual ticks from all around Finland. The results of our field studies suggest that both tick abundance and B. burgdorferi s.l. prevalence have increased in Southwest Finland between the twelve years separating the two studies conducted there. In addition to B. burgdorferi s.l., Borrelia miyamotoi, Rickettsia helvetica and Rickettsia monacensis have been detected from collected ticks. Borrelia miyamotoi, R. helvetica and R. monacensis have also been detected from larval tick samples. Currently we are working on the massive data gathered in the national collection campaign. While laboratory analyses have only just been started, identification and mapping of the received tick samples has already revealed that I. persulcatus is much more prevalent in Finland than previously thought. Furthermore, with the coordinate data from both the questionnaire survey and tick collection campaign, we have been able to accurately map the geographical distributions of both I. ricinus and I. persulcatus in Finland.</p

Tick-borne pathogens in Finland : comparison of Ixodes ricinus and I-persulcatus in sympatric and parapatric areas

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.Peer reviewe

First evidence of Ixodiphagus hookeri (Hymenoptera: Encyrtidae) parasitization in Finnish castor bean ticks (Ixodes ricinus)

Ixodiphagus hookeri (Hymenoptera: Encyrtidae) is a parasitoid wasp specialized in parasitizing the larvae and nymphs of ticks (Acari: Ixodidae). As parasitized ticks die prior to reproduction, I. hookeri is seen as a prime biological control agent candidate. Despite this, little is known of their occurrence or ecology in northern Europe. The main aim of the current study was to determine whether adult wasps or parasitized ticks can be found from a tick-infested island in southwestern Finland, using field collections and molecular methods. Following the initial discovery of an adult I. hookeri female on Seili Island, we set out to collect further specimens via sweep netting and Malaise trappings between May and October 2017. Furthermore, 1310 Ixodes ricinus (1220 nymphs, 90 adults) collected from the island during 2012-2014 were screened for I. hookeri DNA using qPCR. Whereas no further wasp specimens could be collected via sweep netting or Malaise trappings, I. hookeri DNA was consistently detected in I. ricinus nymphs (annual minimum infection rates in 2012, 2013, and 2014: 2.3, 0.4, and 0.5%, respectively), whereas all adult samples were negative. Although the annually repeated detections of parasitized ticks suggest that the wasp inhabits the island, further field and molecular surveys are needed to more comprehensively determine the status and stability of the population

The importance of study duration and spatial scale in pathogen detection-evidence from a tick-infested island

Ticks (Acari: Ixodoidea) are among the most common vectors of zoonotic pathogens worldwide. While research on tick-borne pathogens is abundant, few studies have thoroughly investigated small-scale spatial differences in their occurrence. Here, we used long-term cloth-dragging data of Ixodes ricinus and its associated, known and putative pathogens (Borrelia burgdorferi s.l., Borrelia miyamotoi, Anaplasma phagocytophilum, Rickettsia spp., Candidatus Neoehrlichia mikurensis, Bartonella spp., Babesia spp., and tick-borne encephalitis virus, TBEV) from a small, well-studied island in southwestern Finland to analyze potential temporal and spatial differences in pathogen prevalence and diversity between and within different biotopes. We found robust evidence indicating significant dissimilarities in B. burgdorferi s.l., A. phagocytophilum, Rickettsia, and Ca. N. mikurensis prevalence, even between proximal study areas on the island. Moreover, during the 6 years of the ongoing study, we witnessed the possible emergence of TBEV and Ca. N. mikurensis on the island. Finally, the stable occurrence of a protozoan pathogen that has not been previously reported in Finland, Babesia venatorum, was observed on the island. Our study underlines the importance of detailed, long-term tick surveys for public health. We propose that by more precisely identifying different environmental factors associated with the emergence and upkeep of enzootic pathogen populations through rigorous longitudinal surveys, we may be able to create more accurate models for both current and future pathogen distributions.Peer reviewe

Absence of Francisella tularensis in Finnish Ixodes ricinus and Ixodes persulcatus ticks

Abstract Francisella tularensis subsp. holarctica is the causative agent of tularaemia in Europe. Finland is a high-incidence region for tularaemia, with mosquito bites as the most common sources of infection. However, in Central and Western Europe, ticks (Acari: Ixodidae) have been suggested as the main vectors. Indeed, several studies have reported the pathogen from the locally most common human-biting tick species, Ixodes ricinus. In Finland, the occurrence of the pathogen in ticks has started receiving attention only recently. Here, we collate previous tick screening data from Finland regarding F. tularensis as well as present the results from a novel screening of roughly 15 000 I. ricinus and I. persulcatus collected from across the country. In total, 14 878 ticks collected between 2015 and 2020 were screened for F. tularensis using a TaqMan-based qPCR assay targeting the 23 KDa gene. The combined screening efforts of the current and previous studies, encompassing roughly 20 000 ticks, did not find any positive ticks. Given the negative results despite the considerable sample size, it appears that the pathogen is not circulating in local tick populations in Finland. We discuss some possible reasons for the lack of the bacterium in ticks in this high-incidence region of tularaemia