Integrating tick density and park visitor behaviors to assess the risk of tick exposure in urban parks on Staten Island, New York

Background Public green spaces are important for human health, but they may expose visitors to ticks and tick-borne pathogens. We sought to understand risk and drivers of tick-preventative behavior in three popular parks on Staten Island, NY, USA by integrating tick hazard and park visitors’ behaviors. Methods From 20 May to 19 August 2019, ticks were collected via drag cloth sampling in multiple parks, sites, and habitats to estimate tick density. Human behavior was assessed by observing usage (time spent and activity type) in each site and habitat. To evaluate risk of tick exposure, we compared park usage by demographics across sites and compared individual exposure time per site and habitat. To assess visitors’ tick prevention behaviors, a knowledge, attitude, and practices (KAP) survey was administered. Results Three tick species (Ixodes scapularis, Amblyomma americanum and Haemaphysalis longicornis) were collected. The density of nymphs was heterogenous across parks, with the greatest density in unmaintained herbaceous habitats and trails. The fewest people entered the highest tick risk park and within-park locations. The KAP survey revealed that most respondents (N= 190) could not identify a nymphal stage tick when shown examples of various arthropods. Interviewees identified parks as the main location for tick exposure, but most believed they themselves had minimal risk for tick encounter. Consequently, many visitors did not conduct tick checks. People were most likely to practice tick checks if they knew multiple prevention methods and perceived a high likelihood of tick encounter. Conclusions By integrating acarological indices and park visitor behaviors we found a mismatch between the areas with higher tick densities and areas more frequently used by park visitors. However, this exposure risk varied among demographic groups and the type of activities. Moreover, the use of preventative measures was associated with the perceived probability of tick encounter and knowledge of tick habitat, which would modify the ultimate risk of tick encounter and disease given exposure. Our research is a first step towards identifying visitor risk, attitudes, and practices that could be targeted by optimized messaging strategies for tick bite prevention among park visitors.

Mechanistic movement models reveal ecological drivers of tick-borne pathogen spread

Identifying ecological drivers of tick-borne pathogen spread has great value for tick-borne disease management. However, theoretical investigations into the consequences of host movement behaviour on pathogen spread dynamics in heterogeneous landscapes remain limited because spatially explicit epidemiological models that incorporate more realistic mechanisms governing host movement are rare. We built a mechanistic movement model to investigate how the interplay between multiple ecological drivers affects the risk of tick-borne pathogen spread across heterogeneous landscapes. We used the model to generate simulations of tick dispersal by migratory birds and terrestrial hosts across theoretical landscapes varying in resource aggregation, and we performed a sensitivity analysis to explore the impacts of different parameters on the infected tick spread rate, tick infection prevalence and infected tick density. Our findings highlight the importance of host movement and tick population dynamics in explaining the infected tick spread rate into new regions. Tick infection prevalence and infected tick density were driven by predictors related to the infection process and tick population dynamics, respectively. Our results suggest that control strategies aiming to reduce tick burden on tick reproduction hosts and encounter rate between immature ticks and pathogen amplification hosts will be most effective at reducing tick-borne disease risk.

Distribution of Dermacentor andersoni (Acari: Ixodidae) in Grassland Regions of Alberta, Canada

The geographic distribution of the Rocky Mountain wood tick, Dermacentor andersoni Stiles, was determined in Alberta, Canada, by drag sampling at 86 and 89 sites during 2011 and 2012, respectively. Tick density and prevalence varied between years, averaging (range) 1.0 (0–26.2) and 5.9 (0–110) ticks/1,000 m2 in 2011 and 2012, respectively. Ticks were detected at 24.4% and 42.7% of the sites sampled in each respective year. Tick density and presence declined in a northerly direction to 51.6°N and in a westerly direction to ca. 113°W, except for a small area of high density at the edge of the Rocky Mountains in the southeastern portion of the province. Ticks were most abundant in the Dry Mixedgrass and Montane natural subregions and in areas with Brown Chernozemic, Regosol, and Solodized Solonetzic great soil groups. A logistic regression model indicated that tick presence was increased in the Dry Mixedgrass natural subregion and in regions with greater temperatures during the previous summer and normal winter precipitation but was reduced in areas with Dark Brown Chernozemic soils. The model will be useful for predicting tick presence and the associated risk of tick-borne diseases in the province.

Climate change and tick-borne encephalitis in the Greater Alpine region.

Tick-borne encephalitis (TBE) is a viral tick-borne disease. The distribution of human TBE cases ranges from the French departments bordering Germany through Central and Eastern Europe, the Caucasus and Kazakhstan to the Far East of Russia and China. In this expert opinion, TBE is described in the greater area of the European Alps, denoted as the Greater Alpine Region (GAR). It also includes reported tick-borne encephalitis cases and evidence for climate change impacts on tick density and distribution as well as the prevalence and intensity of TBE.

Landscape determinants of density of blacklegged ticks, vectors of Lyme disease, at the northern edge of their distribution in Canada

In eastern North America, including Canada, Lyme disease is caused by Borrelia burgdorferi sensu stricto and transmitted to humans by the blacklegged tick, Ixodes scapularis. The last decade has seen a growing incidence of Lyme disease in Canada, following the northward range expansion of I. scapularis tick populations from endemic areas in eastern United States. This may be attributable to movement of the many hosts that they parasitize, including songbirds, deer and small mammals. In this study, we wanted to test the effect of spatial, temporal and ecological variables, on blacklegged tick density and infection rates, near the northern limit of their distribution in Ontario and Quebec, Canada. We found an effect of both proportion of forested areas and distance to roads, on density of I. scapularis ticks and prevalence of infection by B. burgdorferi. We also found an effect of both sampling year and ordinal sampling data on prevalence of infection by B. burgdorferi. In six adjacent sites showing evidence of reproducing I. scapularis populations, we found that forest composition and structure influenced density of I. scapularis ticks. Our results suggest that blacklegged tick density and infection rate in Canada may be influenced by a variety of factors.

How the Distance Between Drag-Cloth Checks Affects the Estimate of Adult and Nymphal Ixodes scapularis (Acari: Ixodidae) Density

Drag-cloth sampling is the most commonly used method to sample for ticks. A cloth is dragged along the ground and checked for ticks at regular intervals to count ticks before they drop off. The distance between drag-cloth checks differs between studies, which could result in lower density estimates for studies with greater distances between checks. Here, we measured this effect by 1) calculating the rate at which nymphal and adult Ixodes scapularis Say ticks drop off the cloth per meter dragged and 2) measuring tick density by drag-cloth sampling with three different drag-cloth check interval distances. We found a higher drop-off rate for adult ticks, 0.083/m, than nymphal ticks, 0.047/m. The estimated density of ticks decreased with increasing check interval distance. Our results not only highlight the importance of accounting for check interval distance when estimating tick density, but also provide the first estimate of nymphal I. scapularis drop-off rate.

Model of Risk of Exposure to Lyme Borreliosis and Tick-Borne Encephalitis Virus-Infected Ticks in the Border Area of the Czech Republic (South Bohemia) and Germany (Lower Bavaria and Upper Palatinate)

In Europe, Lyme borreliosis (LB) and tick-borne encephalitis (TBE) are the two vector-borne diseases with the largest impact on human health. Based on data on the density of host-seeking Ixodes ricinus ticks and pathogen prevalence and using a variety of environmental data, we have created an acarological risk model for a region where both diseases are endemic (Czech Republic—South Bohemia and Germany—Lower Bavaria, Upper Palatinate). The data on tick density were acquired by flagging 50 sampling sites three times in a single season. Prevalence of the causative agents of LB and TBE was determined. Data on environmental variables (e.g., altitude, vegetation cover, NDVI, land surface temperature) were obtained from various sources and processed using geographical information systems. Generalized linear models were used to estimate tick density, probability of tick infection, and density of infected ticks for the whole area. A significantly higher incidence of human TBE cases was recorded in South Bohemia compared to Bavarian regions, which correlated with a lower tick density in Bavaria. However, the differences in pathogen prevalence rates were not significant. The model outputs were made available to the public in the form of risk maps, indicating the distribution of tick-borne disease risk in space.