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Factors responsible for Ixodes ricinus presence and abundance across a natural-urban gradient
Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.ORCID iD: 0000-0002-8237-4254
Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.ORCID iD: 0000-0002-6598-1976
Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.ORCID iD: 0000-0001-8137-5661
Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.ORCID iD: 0000-0002-7043-9815
2023 (English)In: PLOS ONE, E-ISSN 1932-6203, Vol. 18, no 5, article id e0285841Article in journal (Refereed) Published
Abstract [en]

To better understand the spatial distribution of the common tick Ixodes ricinus, we investigated how local site factors and landscape characteristics influence tick presence and abundance in different greenspaces along the natural-urban gradient in Stockholm County, Sweden. Ticks and field data were collected in 2017 and 2019 and analyzed in relation to habitat type distributions estimated from land cover maps using geographical information system (GIS). A total of 1378 (992 larvae, 370 nymphs, 13 females, and 3 males) questing ticks were collected from 295 sampling plots in 47 different greenspaces. Ticks were present in 41 of the 47 greenspaces and our results show that both local site features such as vegetation height, and landscape characteristics like the amount of mixed coniferous forest, significantly affect tick abundance. Tick abundance was highest in rural areas with large natural and seminatural habitats, but ticks were also present in parks and gardens in highly urbanized areas. Greenspaces along the natural-urban gradient should be included in surveillance for ticks and tick-borne diseases, including highly urbanized sites that may be perceived by the public as areas with low risk for tick encounters.

Place, publisher, year, edition, pages
Public Library of Science (PLoS), 2023. Vol. 18, no 5, article id e0285841
Keywords [en]
Forests, Ricinus, Larvae, Nymphs, Urbanization, Ticks, Ixodes, Forest ecology
National Category
Environmental Sciences
Research subject
Environmental Studies; Baltic and East European studies
Identifiers
URN: urn:nbn:se:sh:diva-51517DOI: 10.1371/journal.pone.0285841ISI: 000993290400020PubMedID: 37195993Scopus ID: 2-s2.0-85159760656OAI: oai:DiVA.org:sh-51517DiVA, id: diva2:1758496
Part of project
Human – environment interactions and the epidemiological periurban landscape of tick-borne diseases, The Foundation for Baltic and East European Studies
Funder
The Foundation for Baltic and East European Studies, 52/2018Available from: 2023-05-23 Created: 2023-05-23 Last updated: 2024-02-27Bibliographically approved
In thesis
1. Ticks - ecology, new hazards, and relevance for public health
Open this publication in new window or tab >>Ticks - ecology, new hazards, and relevance for public health
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Fästingar - ekologi, nya riskfaktorer och deras betydelse för folkhälsan
Abstract [en]

Ticks and tick-borne diseases are ranking second only to mosquitoes as vectors of pathogens responsible for diseases in both humans and domestic animals. In the countries around the Baltic Sea, two medically important tick species are increasing both in range and abundance, and the public health threat posed by tick-borne diseases in this area is steadily growing. The aim of this thesis was to study the eco-epidemiological dynamics and mechanisms of ticks and bacterial tick-borne pathogens along the natural-urban gradient.

Green spaces have become important intersections between humans, domestic animals, ticks, and tick-borne pathogens. Along the natural-urban gradient in Stockholm County, Sweden, we examined the impact of green space characteristics on tickabundance and pathogens prevalence. In this study all questing ticks were molecularly identified as Ixodes ricinus. Questing ticks were abundant in natural and seminatural habitats, but also present in urbanized parks. Important drivers of tickabundance included significant negative effects of local vegetation height and positiveeffects of mixed coniferous forests in the surrounding landscape.

The prevalence of Borrelia burgdorferi sensu lato was 24% and that of Anaplasma phagocytophilum 7.5%. B. miyamotoi was found at a few sites with a prevalence of 0.9%. The dominant B. burgdorferi (s.l.) genospecies was B. afzelii. Tree stem density had a significant positive effect on B. burgdorferi (s.l.) prevalence. Broadleaved forests and total forest edge had significant positive effects on A. phagocytophilum prevalence, persisting even in highly urbanized areas. The tick-borne disease equine granulocytic anaplasmosis (EGA) significant increased from 2002 to 2015, with a yearly peak in late summer and early fall.

The public health risk for tick-borne diseases in an urban green space was estimated from hazard data on tick abundances and pathogen prevalence combined with exposure data using residential population densities and green space visitor numbers. The results indicated a medium to high risk of tick-borne diseases at most sites. Structured interviews with visitors showed that even if visitors showed a high tick awareness and attempted to avoid ticks, most protective measures were only practiced during specific recreational activities.

The findings from this doctoral project show a notable risk of encountering ticks and tick-borne pathogens along the entire natural-urban gradient, even in highly urbanized areas traditionally perceived as having a low risk. The information on the eco-epidemiological drivers of EGA is important also for the medical health field since the agent causing EGA is identical to the agent causing human disease. Despite ticks and their pathogens green spaces still continue to play a vital role in public health, but the omnipresent risk of tick-borne diseases highlights the need for public health initiatives to mitigate this risk. 

Abstract [sv]

Fästingar är näst efter myggor de viktigaste vektorerna för spridning av sjukdomar både till människor och husdjur. I länderna runt Östersjön finns två medicinskt viktiga fästingarter som ökar i utbredning och antal, vilket också utgör ett ökat hot mot folkhälsan. Syftet med avhandlingen var att studera eko-epidemiologisk dynamik och viktiga mekanismer för spridningen av fästingar och fästingburna bakterier i en urban gradient.

Grönområden i och runt städer utgör mötesplatser för människor, husdjur, fästingar och fästingburna patogener. I Stockholms län undersöktes effekterna av grönområdenas egenskaper på förekomst av fästingar och deras patogener utefter den urbana gradienten. Alla insamlade fästingar artbestämdes med molekylära metoder, och samtliga tillhörde arten Ixodes ricinus. Fästingar var vanliga i rurala områden och naturliga miljöer, men förekom även i urbana parker. Viktiga faktorer för förekomst av fästingar var den signifikant negativa effekten av vegetationshöjd vid insamlingsplatsen, och den signifikant positiva effekten av barrblandskog i det omgivande landskapet.

I studien av patogener var prevalensen av Borrelia burgdorferi sensu lato 24% och för Anaplasma phagocytophilum 7.5%. Fästingar infekterade med B. miyamotoi påträffades vid några få platser med en prevalens på 0.9%. Den dominerande arten inom gruppen av B. burgdorfgeri (s.l.) var B. afzelii. Trädtäthet runt insamlingsplatsen hade en signifikant positiv effekt på prevalensen av B. burgdorferi (s.l.). Utbredningen av lövskogar och skogskanter hade signifikant positiva effekter på prevalensen av A. phagocytophilum, och fästingar infekterade med A. phagocytophilum förekom även i urbana parker. Den fästingburna sjukdomen granulocytär anaplasmos hos häst, ökade signifikant från 2002 till 2015, med flest fall på sensommar och tidig höst.

Folkhälsorisker för fästingburna sjukdomar i ett urbant grönområde uppskattades med hjälp av information om fästingförekomst, patogenprevalens, befolkningstäthet och besöksantal. Resultatet visade en måttlig till hög risk för fästingburna sjukdomar i hela det undersökta grönområdet. Vid intervjuer med besökare påvisades en hög medvetenhet om fästingar och fästingspridda sjukdomar, men att skyddsåtgärder endast tillämpades vid specifika fritidsaktiviteter såsom bärplockning.

Resultatet från avhandlingen visar på en betydande risk för spridning av fästingburna sjukdomar längs med hela den urbana gradienten, inklusive områden som traditionellt ansetts ha en låg risk. Resultaten som visar på eko-epidemiologiska mekanismer för spridning av granulocytär anaplasmos hos häst är relevanta också ur ett folkhälsoperspektiv eftersom bakterierna orsakar sjukdom även hos människor. Trots risker med fästingar och deras sjukdomar är grönområden ytterst viktiga för folkhälsan utifrån andra hälsoaspekter, men det behövs initiativ och medvetenhet för att motverka riskerna.

Place, publisher, year, edition, pages
Huddinge: Södertörns högskola, 2024. p. 196
Series
Södertörn Doctoral Dissertations, ISSN 1652-7399 ; 226
Keywords
Baltic Sea region, eco-epidemiology, habitat, Ixodes persulcatus, Ixodes ricinus, landscape, risk, urbanization
National Category
Ecology
Research subject
Environmental Studies; Baltic and East European studies
Identifiers
urn:nbn:se:sh:diva-53598 (URN)978-91-89504-70-7 (ISBN)978-91-89504-71-4 (ISBN)
Public defence
2024-03-22, MB505, Alfred Nobels allé 7, Huddinge, 10:00 (English)
Opponent
Supervisors
Funder
The Foundation for Baltic and East European Studies, 52/12
Available from: 2024-02-29 Created: 2024-02-27 Last updated: 2024-03-01Bibliographically approved

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Janzén, ThereseHammer, MonicaPetersson, MonaDinnétz, Patrik

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