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.

Evaluation of factors influencing tick bites and tick-borne infections: a longitudinal study

“…Many unrecorded factors can influence human exposure to ticks, but owning a furred animal does not seem to be an isolated risk factor. A Scandinavian study on risk factors neither found an association between pet ownership and reported tick bites, but between outdoor activities and reported tick bites [ 50 ].…”

A Mini-Review of Ixodes Ticks Climate Sensitive Infection Dispersion Risk in the Nordic Region

“…Ticks occur less in pine forest and least in grass and heath, explained by ticks being exposed to more desiccating weather conditions in open vegetation [ 27 , 29 ]. Several studies have linked the presence of ticks with the incidence of pathogens in ticks, humans, and animals [ 11 , 30 , 31 , 32 ]. In general, the findings confirm that not all, but varying percentages of ticks are carriers of the pathogens, sometimes more in females and in nymph stages.…”

“…Several Nordic studies on ticks and TBDs have shown that I. ricinus has changed its distribution in recent decennia [ 20 , 45 , 57 , 58 ], with a northward migration of approximately 400 km within the past 20–30 years in Norway [ 58 , 59 ], up to 150–250 km north of the Arctic Circle, though with a sparser presence north of 65° N [ 60 , 61 ]. A recent study by Hvidsten et al [ 45 ] found that the northernmost permanent I. ricinus population was located at 66.22° N at the coast, although this study did not have national coverage and used only one method (flagging) with low efficiency, and cannot therefore be used to verify presence or absence [ 32 ]. Nevertheless, the study suggests presence at a high latitude, and the range expansion indicated in the area of 69° N (northern tip of Sweden) is in line with the distributional limit predicted previously [ 20 , 28 , 31 ].…”

“…Finally, there are indications that selective animal breeding strategies—at least in sheep—may reduce tick infestation and infections [ 70 ]. Besides a focus on management measures, continued control of the prevalence of pathogens in ticks, and disease data from public health registries, are both important, and remain the main sources for the study of the risk of tick-borne diseases [ 32 ]. Studies on pathogen carriage in ticks thus far suggest lower pathogen load in ticks in northern Norway compared to southern Norway [ 31 ].…”

Are Orienteers Protected Enough against Tick Bites? Estimating Human Exposure to Tick Bites through a Participative Science Survey during an Orienteering Competition

“…The expected proportion of orienteers bitten by ticks is therefore between 33% and 62% during the six days of the competition and between 10% to 42% per day, which is in either case very high. For comparison with general populations of other countries, a range of 45–60% of respondents reported finding attached ticks over a preceding 12-month period in surveys conducted in Scandinavia [ 47 ] and in North-West Italy [ 48 ]. In endemic areas of Lyme disease in USA, this proportion was in the range of 10–37% [ 25 ], and in France it has been estimated that only 4.1% of the general population was bitten over a period of 12 months [ 46 ].…”