Spatial tick bite exposure and associated risk factors in Scandinavia

ABSTRACT

Tick-borne diseases are emerging and re-emerging threats causing public health concerns in Europe and North America. Prevention and control requires understanding of human exposure and behaviour. The aim was to measure exposure to tick bites across Scandinavia, its spatial distribution and the associated risk factors.

Methods

We sent a web-based survey to a randomly chosen population and analysed answers by Principal Component Analysis and Chi-Square. Individual responses were aggregated at the municipality level to assess the spatial distribution of bites.

Results

Nearly 60% of adults reported bites at low levels (1-5 bites); however, the majority were not in their resident municipality. We found two spatial profiles: In their home municipalities, people were most often bitten in less, but not the least, urbanized areas. When visiting other municipalities, people were most frequently bitten in peri-urban areas. Running/walking in the forest, gardening, and paddling/rowing were activities most strongly associated with bites.

Conclusion

Tick bites affect the entire Scandinavian population, with a higher risk in Sweden compared to Denmark and Norway. The frequency of observation of ticks in the environment or on pets might be used as a proxy for the actual risk of exposure to tick bites. Our results indicates that urban-dwelling outdoor enthusiasts and inhabitants of rural areas must be equally targeted for prevention campaigns.

KEYWORDS:

• Ixodes ricinus
• tick
• tick bite
• Norway
• Sweden
• Denmark

Acknowledgments

We gratefully acknowledge comments received on the draft questionnaire by several ScandTick project members. Sincere thanks to Emily Jenkins (Professor at University of Saskatchewan, Canada) for critically reviewing the paper, edits, and discussions. Gratitude to Richard White (Norwegian Public Health Institute) for assisting in R-codes when needed.

Authors’ contributions

SJ, DS, AB, KAK, MTJ and LV designed the questionnaire and performed pilot testing and contributed to the design of the study. SJ wrote the manuscript, with notable input from SOV. SJ and SOV carried out the data analysis and interpretation. SOV elaborated the maps. All authors edited, revised and approved the final manuscript.

Ethics declaration

Information on approval of the work by an ethics committee

Sweden: The study was approved by the Regional Ethical Review Board at the University of Gothenburg (decision number 714-16). Participants were adults (at least 18 year old) who gave informed consent. Participation was voluntary. Results are reported so that individual participants cannot be identified.

For Norway and Denmark, no ethical approval was needed since individual participants cannot be identified and the researchers have not had directly contact with the respondents (For Norway see § 4d i helseforskningsloven and REK committee (https://lovdata.no/dokument/NL/lov/2008-06-20-44); for Denmark see komitelovens § 14, stk 2)

Disclosure statement

The authors declare that they have no competing interests

Availability of data and materials

The data are accessible upon request.

Notes

* If got several children only asked about the oldest child

Additional information

Funding

This study was partly funded by the EU Interreg project ScandTick Innovation, grant number 20200422;EU Interreg [20200422].