Use of Mass-Participation Outdoor Events to Assess Human Exposure to Tickborne Pathogens

Tick hazard in the South Downs National Park (UK): species, distribution, key locations for future interventions, site density, habitats

Background

South Downs National Park (SDNP) is UK's most visited National Park, and a focus of tick-borne Lyme disease. The first presumed UK autochthonous cases of tick-borne encephalitis and babesiosis were recorded in 2019-20. SDNP aims to conserve wildlife and encourage recreation, so interventions are needed that reduce hazard without negatively affecting ecosystem health. To be successful these require knowledge of site hazards.

Methods

British Deer Society members submitted ticks removed from deer. Key potential intervention sites were selected and six 50 m2 transects drag-sampled per site (mostly twice yearly for 2 years). Ticks were identified in-lab (sex, life stage, species), hazard measured as tick presence, density of ticks (all life stages, DOT), and density of nymphs (DON). Sites and habitat types were analysed for association with hazard. Distribution was mapped by combining our results with records from five other sources.

Results

A total of 87 Ixodes ricinus (all but one adults, 82% F) were removed from 14 deer (10 Dama dama; three Capreolus capreolus; one not recorded; tick burden, 1-35) at 12 locations (commonly woodland). Five key potential intervention sites were identified and drag-sampled 2015-16, collecting 623 ticks (238 on-transects): 53.8% nymphs, 42.5% larvae, 3.7% adults (13 M, 10 F). Ticks were present on-transects at all sites: I. ricinus at three (The Mens (TM); Queen Elizabeth Country Park (QECP); Cowdray Estate (CE)), Haemaphysalis punctata at two (Seven Sisters Country Park (SSCP); Ditchling Beacon Nature Reserve (DBNR)). TM had the highest DOT at 30/300 m2 (DON = 30/300 m2), followed by QECP 22/300 m2 (12/300 m2), CE 8/300 m2 (6/300 m2), and SSCP 1/300 m2 (1/300 m2). For I. ricinus, nymphs predominated in spring, larvae in the second half of summer and early autumn. The overall ranking of site hazard held for DON and DOT from both seasonal sampling periods. DBNR was sampled 2016 only (one adult H. punctata collected). Woodland had significantly greater hazard than downland, but ticks were present at all downland sites. I. ricinus has been identified in 33/37 of SDNPs 10 km2 grid squares, Ixodes hexagonus 10/37, H. punctata 7/37, Dermacentor reticulatus 1/37.

Conclusions

Mapping shows tick hazard broadly distributed across SDNP. I. ricinus was most common, but H. punctata's seeming range expansion is concerning. Recommendations: management of small heavily visited high hazard plots (QECP); post-visit precaution signage (all sites); repellent impregnated clothing for deerstalkers; flock trials to control H. punctata (SSCP, DBNR). Further research at TM may contribute to knowledge on ecological dynamics underlying infection density and predator re-introduction/protection as public health interventions. Ecological research on H. punctata would aid control. SDNP Authority is ideally placed to link and champion policies to reduce hazard, whilst avoiding or reducing conflict between public health and ecosystem health.

Aseptic Meningitis Linked to Borrelia afzelii Seroconversion in Northeastern Greece: An Emerging Infectious Disease Contested in the Region

Borreliosis (Lyme disease) is a zoonosis, mediated to humans and small mammals through specific vectors (ticks), with increasing global incidence. It is associated with a variety of clinical manifestations and can, if not promptly recognized and left untreated, lead to significant disability. In Europe, the main Borrelia species causing disease in humans are Borrelia burgdorferi s.s., Borrelia afzelii, Borrelia garinii, and Borrelia spielmanii. The Ixodes ricinus tick is their principal vector. Although Lyme disease is considered endemic in the Balkan region and Turkey, and all three main Lyme pathogens have been detected in ticks collected in these countries, autochthonous Lyme disease remains controversial in Greece. We report a case of aseptic meningitis associated with antibody seroconversion against Borrelia afzelii in a young female patient from the prefecture of Thasos without any relevant travel history. The patient presented with fever and severe headache, and the cerebrospinal fluid examination showed lymphocytic pleocytosis. Serum analysis was positive for specific IgG antibodies against Borrelia afzelii. In the absence of typical erythema migrans, serological evidence of infection is required for diagnosis. Although atypical in terms of clinical presentation, the seasonality and geographical location of potential disease transmission in the reported patient should raise awareness among clinicians for a still controversial and potentially underreported emerging infectious disease in Greece.

Linking human tick bite risk with tick abundance in the environment: A novel approach to quantify tick bite risk using orienteers in Scotland

The rate that people are bitten by ticks is critical in determining the risk of tick-borne infections but is rarely quantified accurately. Often tick abundance in the environment is used as a proxy for tick bite risk, but the relationship with risk is poorly understood. We used a novel citizen science approach to measure tick bite rate in orienteers, to assess the relationship between tick abundance and tick bite risk and to identify risk factors for tick bites. Eleven orienteering events were attended in Scotland between August 2018 and September 2019. The number of tick bites in orienteers, and the time and distance of activity were collected using an online questionnaire. Tick abundance in the same areas used for the orienteering events was estimated by surveying ticks on ground vegetation using blanket drags. Among orienteers, mean incidence was 409 tick bites per 1,000 person-hours. Tick abundance and tick bite rate were strongly correlated, indicating that data from questing tick surveys is a useful proxy for the risk of human tick bites. Tick bite rate was better explained by the activity duration than distance covered and was higher in orienteers that ran earlier in the day, exposed to higher temperatures and in woodland habitats. This study highlights the value of the citizen science approach used, which crucially included submission of activity reports both with and without ticks, to generate robust data on tick bite rate. Accurately measuring tick bite rate and understanding environmental factors that influence it are essential in mitigating the risk of tick-borne diseases.

Habitat suitability map of <em>Ixodes ricinus</em> tick in France using multi-criteria analysis

The tick Ixodes ricinus is widely distributed across Europe and is responsible for the transmission of several pathogens to humans and animals. In this study, we used a knowledge-based method to map variations in habitat suitability for I. ricinus ticks throughout continental France and Corsica. The multi-criteria decision analysis (MCDA) integrated four major biotic and abiotic factors known to influence tick populations: climate, land cover, altitude and the density of wild ungulates. For each factor, habitat suitability index (HSI) values were attributed to different locations based on knowledge regarding its impact on tick populations. For the MCDA, two methods of factor combination were tested, additive and multiplicative, both which were evaluated at the spatial scales of departments and local municipalities. The resulting habitat suitability maps (resolution=100x100 m) revealed that conditions are suitable for I. ricinus over most of France and Corsica. Particularly suitable habitats were located in central, north-eastern and south-western France, while less-suitable habitats were found in the Mediterranean and mountainous regions. To validate the approach, the HSI scores were compared to field data of I. ricinus nymph abundance. Regardless of scale, the correlation between abundance indicator and HSI score was stronger for the additive than for the multiplicative approach. Overall, this study demonstrates the value of MCDA for estimating habitat suitability maps for I. ricinus abundance, which could be especially useful in highlighting areas of the tick's distribution where preventive measures should be prioritised.

Bacterial Pathogens and Symbionts Harboured by Ixodes ricinus Ticks Parasitising Red Squirrels in the United Kingdom

Red squirrels (Sciurus vulgaris) are native to most of Eurasia; in much of the United Kingdom, they have been supplanted by the non-native grey squirrel, and are considered an endangered species. Very little is known about the range of tick-borne pathogens to which UK red squirrels are exposed. As part of trap-and-release surveys examining prevalence of Mycobacterium spp. in red squirrel populations on two UK islands, Ixodes ricinus ticks were removed from squirrels and PCR screened for Borrelia spp., intracellular arthropod-borne bacteria and the parasitic wasp Ixodiphagus hookeri. At both sites, the most commonly encountered tick-transmitted bacterium was Borrelia burgdorferi sensu lato (overall minimum prevalence 12.7%), followed by Anaplasma phagocytophilum (overall minimum prevalence 1.6%). Single ticks infected with Spiroplasma were found at both sites, and single ticks infected with Borrelia miyamotoi or an Ehrlichia sp. at one site. Ticks harbouring Wolbachia (overall minimum prevalence 15.2%) were all positive for I. hookeri. Our study shows that UK red squirrels are potentially exposed to a variety of bacterial pathogens via feeding ticks. The effects on the health and survival of this already vulnerable wildlife species are unknown, and further studies are needed to evaluate the threat posed to red squirrels by Borrelia and other tick-borne pathogens.

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

Mass-participation events in temperate forests are now well-established features of outdoor activities and represent high-risk activities regarding human exposition to tick bites. In this study we used a citizen science approach to quantify the space-time frequency of tick bites and undetected tick bites among orienteers that participated in a 6-day orienteering competition that took place in July 2018 in the forests of Eastern France, and we looked at the use and efficacy of different preventive behaviors. Our study confirms that orienteers are a high-risk population for tick bites, with 62.4% of orienteers bitten at least once during the competition, and 2.4 to 12.1 orienteers per 100 orienteers were bitten by ticks when walking 1 km. In addition, 16.7% of orienteers bitten by ticks had engorged ticks, meaning that they did not detect and remove their ticks immediately after the run. Further, only 8.5% of orienteers systematically used a repellent, and the use of repellent only partially reduced the probability of being bitten by ticks. These results represent the first attempt to quantify the risk of not immediately detecting a tick bite and provide rare quantitative data on the frequency of tick bites for orienteers according to walking distance and time spent in the forest. The results also provide information on the use of repellent, which will be very helpful for modeling risk assessment. The study also shows that prevention should be increased for orienteers in France.

Tick-borne encephalitis virus (TBEV) prevalence in field-collected ticks (Ixodes ricinus) and phylogenetic, structural and virulence analysis in a TBE high-risk endemic area in southwestern Germany

BACKGROUND

Tick-borne encephalitis (TBE) is the most common viral CNS infection with incidences much higher than all other virus infections together in many risk areas of central and eastern Europe. The Odenwald Hill region (OWH) in southwestern Germany is classified as a TBE risk region and frequent case numbers but also more severe infections have been reported within the past decade. The objective of the present study was to survey the prevalence of tick-borne encephalitis virus (TBEV) in Ixodes ricinus and to associate TBEV genetic findings with TBE infections in the OWH.

METHODS

Ticks were collected by the flagging methods supported by a crowdsourcing project implementing the interested public as collectors to cover completely and collect randomly a 3532 km2 area of the OWH TBE risk region. Prevalence of TBEV in I. ricinus was analysed by reversed transcription quantitative real-time PCR. Phylogeographic analysis was performed to classify OWH TBEV isolates within a European network of known TBEV strains. Mutational sequence analysis including 3D modelling of envelope protein pE was performed and based on a clinical database, a spatial association of TBE case frequency and severity was undertaken.

RESULTS

Using the crowd sourcing approach we could analyse a total of 17,893 ticks. The prevalence of TBEV in I. ricinus in the OWH varied, depending on analysed districts from 0.12% to 0% (mean 0.04%). Calculated minimum infection rate (MIR) was one decimal power higher. All TBEV isolates belonged to the European subtype. Sequence analysis revealed a discontinuous segregation pattern of OWH isolates with two putative different lineages and a spatial association of two isolates with increased TBE case numbers as well as exceptional severe to fatal infection courses.

CONCLUSIONS

TBEV prevalence within the OWH risk regions is comparatively low which is probably due to our methodological approach and may more likely reflect prevalence of natural TBEV foci. As for other European regions, TBEV genetics show a discontinuous phylogeny indicating among others an association with bird migration. Mutations within the pE gene are associated with more frequent, severe and fatal TBE infections in the OWH risk region.

A descriptive epidemiological study of the incidence of newly diagnosed Lyme disease cases in a UK primary care cohort, 1998-2016

BACKGROUND

Primary care is likely to see the highest number of Lyme disease patients. Despite this, there is limited published data regarding Lyme disease patients accessing primary care in the UK. We aim to describe trends in the incidence of a new diagnosis, and demographics of patients identified in a primary care electronic health database.

METHODS

A descriptive epidemiological study of Lyme disease coded patients in UK primary care. 3725 patients coded for Lyme disease during 1998-2016 were identified within The Health Improvement Network (THIN). Incidence rates and the demographics of cases identified were described. Poisson regression was used to analyse socio-demographic characteristics of the cases.

RESULTS

There was an increase in annual crude incidence rates, peaking in 2015 at 5.47 (95% CI 4.85-6.14) cases per 100,000 population per year. Multivariable analysis showed there were significant differences in the ages of those affected, incidence of a new diagnosis rose as deprivation levels improved, and that there was a higher incidence of cases living in rural areas compared to urban areas. There was no significant difference between sexes for the UK. Cases were significantly more likely to identify with being white compared to the national population.

CONCLUSIONS

An increasing incidence of patients newly coded with Lyme disease related Read codes was identified using data from a UK national primary care database. By comparing these incidence figures with national laboratory-confirmed surveillance data, a multiplication factor of 2.35 (95%CI 1.81-2.88) can be calculated in order to estimate the annual number of cases seen in primary care. The significant socio-demographic variables associated with a Lyme disease diagnosis likely reflect a complex interplay of socio-economic issues, which needs to be further explored. Future work is needed to examine the treatment and management of patients within this database.

Study of general practitioner consultations for tick bites at high, medium and low incidence areas for Lyme borreliosis in England and Wales

Lyme borreliosis (LB) is a tick-borne disease caused by Borrelia burgdorferi sensu lato complex. In Europe, it is predominately transmitted by the sheep tick, Ixodes ricinus. Compared with other European countries, the United Kingdom (UK) is considered to have a low incidence of LB, although this varies regionally. To determine whether an association exists between tick bite consultations and LB incidence in the UK, retrospective questionnaires were sent to general practitioners (GPs) in high (Wiltshire), medium (Cumbria) and low (Wales) incidence areas. During 2011, the greatest incidence of consultations for tick bites was reported by GPs in Cumbria (204 consultations per 100,000 inhabitants), followed by Wiltshire (160 per 100,000 population) and Wales (54 per 100,000 population). In Wiltshire and Cumbria, GPs predominantly provided advice on tick removal, whilst Welsh GPs mostly advised patients on tick bite prevention. Focusing on Cumbria during 2011-2013, 72.5% of GPs removed ticks from patients (incidence of 101 consultations per 100,000 population), and more GPs diagnosed LB based on clinical features than laboratory-confirmed diagnoses. To date, this is the first study to investigate the incidence of tick bite consultations and LB in England and Wales.

Modelling tick bite risk by combining random forests and count data regression models

The socio-economic and demographic changes that occurred over the past 50 years have dramatically expanded urban areas around the globe, thus bringing urban settlers in closer contact with nature. Ticks have trespassed the limits of forests and grasslands to start inhabiting green spaces within metropolitan areas. Hence, the transmission of pathogens causing tick-borne diseases is an important threat to public health. Using volunteered tick bite reports collected by two Dutch initiatives, here we present a method to model tick bite risk using human exposure and tick hazard predictors. Our method represents a step forward in risk modelling, since we combine a well-known ensemble learning method, Random Forest, with four count data models of the (zero-inflated) Poisson family. This combination allows us to better model the disproportions inherent in the volunteered tick bite reports. Unlike canonical machine learning models, our method can capture the overdispersion or zero-inflation inherent in data, thus yielding tick bite risk predictions that resemble the original signal captured by volunteers. Mapping model predictions enables a visual inspection of the spatial patterns of tick bite risk in the Netherlands. The Veluwe national park and the Utrechtse Heuvelrug forest, which are large forest-urban interfaces with several cities, are areas with high tick bite risk. This is expected, since these are popular places for recreation and tick activity is high in forests. However, our model can also predict high risk in less-intensively visited recreational areas, such as the patchy forests in the northeast of the country, the natural areas along the coastline, or some of the Frisian Islands. Our model could help public health specialists to design mitigation strategies for tick-borne diseases, and to target risky areas with awareness and prevention campaigns.

Using volunteered observations to map human exposure to ticks

Lyme borreliosis (LB) is the most prevalent tick-borne disease in Europe and its incidence has steadily increased over the last two decades. In the Netherlands alone, more than 20,000 citizens are affected by LB each year. Because of this, two Dutch citizen science projects were started to monitor tick bites. Both projects have collected nearly 50,000 geo-located tick bite reports over the period 2006–2016. The number of tick bite reports per area unit is a proxy of tick bite risk. This risk can also be modelled as the result of the interaction of hazard (e.g. tick activity) and human exposure (e.g. outdoor recreational activities). Multiple studies have focused on quantifying tick hazard. However, quantifying human exposure is a harder task. In this work, we make a first step to map human exposure to ticks by combining tick bite reports with a tick hazard model. Our results show human exposure to tick bites in all forested areas of the Netherlands. This information could facilitate the cooperation between public health specialists and forest managers to create better mitigation campaigns for tick-borne diseases, and it could also support the design of improved plans for ecosystem management.

Progress, challenges, and the role of public engagement to improve tick-borne disease literacy

Vector-borne diseases have increased worldwide, facilitated by globalization and variations in climate. Tick and tick-borne disease researchers, veterinarians, medical practitioners, and public health specialists are working to share their expertise on tick ecology, disease transmission, diagnostics, and treatment in order to control tick-borne epidemics and potential pandemics. This review will be a brief overview of the current status of tick-borne diseases, challenges on the scientific and public fronts, and the role of public engagement in improving citizen education within the context of ticks and tick-borne disease research.

Using citizen science to describe the prevalence and distribution of tick bite and exposure to tick-borne diseases in the United States

Tick-borne pathogens are increasing their range and incidence in North America as a consequence of numerous factors including improvements in diagnostics and diagnosis, range expansion of primary vectors, changes in human behavior, and an increasing understanding of the diversity of species of pathogens that cause human disease. Public health agencies have access to human incidence data on notifiable diseases e.g., Borrelia burgdorferi, the causative agent of Lyme disease, and often local pathogen prevalence in vector populations. However, data on exposure to vectors and pathogens can be difficult to determine e.g., if disease does not occur. We report on an investigation of exposure to ticks and tick-borne bacteria, conducted at a national scale, using citizen science participation. 16,080 ticks were submitted between January 2016 and August 2017, and screened for B. burgdorferi, B. miyamotoi, Anaplasma phagocytophilum, and Babesia microti. These data corroborate entomologic investigations of tick distributions in North America, but also identify patterns of local disease risk and tick contact with humans throughout the year in numerous species of ticks and associated pathogens.

Long term survival, health, social functioning, and education in patients with European Lyme neuroborreliosis: nationwide population based cohort study

OBJECTIVE

To estimate long term survival, health, and educational/social functioning in patients with Lyme neuroborreliosis compared with the general population.

DESIGN

Nationwide population based cohort study using national registers.

SETTING

Denmark.

PARTICIPANTS

All Danish residents diagnosed during 1986-2016 as having Lyme neuroborreliosis (n=2067), defined as a positive Borrelia burgdorferi intrathecal antibody test and a clinical diagnosis of Lyme borreliosis, and a comparison cohort from the general population matched on sex and date of birth (n=20 670).

MAIN OUTCOME MEASURES

Mortality rate ratios, incidence rate ratios of comorbidities, and differences in educational and social outcomes.

RESULTS

Mortality among patients with Lyme neuroborreliosis was not higher than in the general population (mortality rate ratio 0.90, 95% confidence interval 0.79 to 1.03). Lyme neuroborreliosis patients had increased risk of haematological (incidence rate ratio 3.07, 2.03 to 4.66) and non-melanoma skin cancers (1.49, 1.18 to 1.88). At diagnosis, Lyme neuroborreliosis patients had slightly higher employment and lower disability pension rates. After five years, patients and comparison cohort members had similar numbers of hospital contacts (difference -0.22, 95% confidence interval -0.45 to 0.02, in-hospital days/year; 0.37, -0.10 to 0.83, outpatient visits/year), employment rates (difference 1.5%, -2.1% to 5.1%), income (difference -1000, -20 000 to 18 000, Danish kroner), days of sick leave (difference -0.3, -3.5 to 3.0, per year), rates of receipt of a disability pension (difference -0.9%, -3.2% to 1.3%), and number of children (difference -0.10, -0.27 to 0.08). More patients were married (difference 4.8%, 2.2% to 7.4%) and had completed high school education (difference 7%, 1% to 12%).

CONCLUSION

A verified diagnosis of Lyme neuroborreliosis had no substantial effect on long term survival, health, or educational/social functioning. Nevertheless, the diagnosis decreased labour market involvement marginally and was associated with increased risk of haematological and non-melanoma skin cancers.