Habitat properties are key drivers of Borrelia burgdorferi (s.l.) prevalence in Ixodes ricinus populations of deciduous forest fragments

Background: The tick Ixodes ricinus has considerable impact on the health of humans and other terrestrial animals because it transmits several tick-borne pathogens (TBPs) such as B. burgdorferi (sensu lato), which causes Lyme borreliosis (LB). Small forest patches of agricultural landscapes provide many ecosystem services and also the disservice of LB risk. Biotic interactions and environmental filtering shape tick host communities distinctively between specific regions of Europe, which makes evaluating the dilution effect hypothesis and its influence across various scales challenging. Latitude, macroclimate, landscape and habitat properties drive both hosts and ticks and are comparable metrics across Europe. Therefore, we instead assess these environmental drivers as indicators and determine their respective roles for the prevalence of B. burgdorferi in I. ricinus. Methods: We sampled I. ricinus and measured environmental properties of macroclimate, landscape and habitat quality of forest patches in agricultural landscapes along a European macroclimatic gradient. We used linear mixed models to determine significant drivers and their relative importance for nymphal and adult B. burgdorferi prevalence. We suggest a new prevalence index, which is pool-size independent. Results: During summer months, our prevalence index varied between 0 and 0.4 per forest patch, indicating a low to moderate disservice. Habitat properties exerted a fourfold larger influence on B. burgdorferi prevalence than macroclimate and landscape properties combined. Increasingly available ecotone habitat of focal forest patches diluted and edge density at landscape scale amplified B. burgdorferi prevalence. Indicators of habitat attractiveness for tick hosts (food resources and shelter) were the most important predictors within habitat patches. More diverse and abundant macro- and microhabitat had a diluting effect, as it presumably diversifies the niches for tick-hosts and decreases the probability of contact between ticks and their hosts and hence the transmission likelihood.[br/] Conclusions: Diluting effects of more diverse habitat patches would pose another reason to maintain or restore high biodiversity in forest patches of rural landscapes. We suggest classifying habitat patches by their regulating services as dilution and amplification habitat, which predominantly either decrease or increase B. burgdorferi prevalence at local and landscape scale and hence LB risk. Particular emphasis on promoting LB-diluting properties should be put on the management of those habitats that are frequently used by humans. In the light of these findings, climate change may be of little concern for LB risk at local scales, but this should be evaluated further

The Freelisting Method

A freelist is a mental inventory of items an individual thinks of within a given category. Freelists reveal cultural " salience " of particular notions within groups, and variation in individuals' topical knowledge across groups. The ease and accuracy of freelist interviewing, or freelisting, makes it ideal for collecting data on health knowledge and beliefs from relatively large samples. Successful freelisting requires researchers to break the research topic into honed categories. Research participants presented with broad prompts tend to " unpack " mental subcategories and may omit (forget) common items or categories. Researchers should find subdomains to present individually for participants to unpack in separate smaller freelists. Researchers may focus the freelist prompts through successive freelisting, pile sorts, or focus group-interviews. Written freelisting among literate populations allows for rapid data collection, possibly from multiple individuals simultaneously. Among nonliterate peoples, using oral freelists remains a relatively rapid method; however, interviewers must prevent bystanders from " contaminating " individual interviewees' lists. Researchers should cross-check freelist responses with informal methods as much as practicable to contextualize and understand the references therein. With proper attention to detail, freelisting can amass high quality data on people's medical understanding, attitudes, and behaviors

Associations of passerine birds, rabbits, and ticks with <it>Borrelia miyamotoi and Borrelia andersonii</it> in Michigan, U.S.A.

<p>Abstract</p> <p>Background</p> <p>Wild birds contribute to maintenance and dissemination of vectors and microbes, including those that impact human, domestic animal, and wildlife health. Here we elucidate roles of wild passerine birds, eastern cottontail rabbits (<it>Sylvilagus floridanus</it>), and <it>Ixodes dentatus</it> ticks in enzootic cycles of two spirochetes, <it>Borrelia miyamotoi</it> and <it>B. andersonii</it> in a region of Michigan where the zoonotic pathogen <it>B. burgdorferi</it> co-circulates.</p> <p>Methods</p> <p>Over a four-year period, wild birds (n = 19,631) and rabbits (n = 20) were inspected for tick presence and ear tissue was obtained from rabbits. Samples were tested for <it>Borrelia</it> spirochetes using nested PCR of the 16S-23S rRNA intergenic spacer region (IGS) and bidirectional DNA sequencing. Natural xenodiagnosis was used to implicate wildlife reservoirs.</p> <p>Results</p> <p><it>Ixodes dentatus,</it> a tick that specializes on birds and rabbits and rarely bites humans, was the most common tick found, comprising 86.5% of the 12,432 ticks collected in the study. The relapsing fever group spirochete <it>B. miyamotoi</it> was documented for the first time in ticks removed from wild birds (0.7% minimum infection prevalence; MIP, in <it>I. dentatus</it>), and included two IGS strains. The majority of <it>B. miyamotoi</it>-positive ticks were removed from Northern Cardinals (<it>Cardinalis cardinalis</it>). <it>Borrelia andersonii</it> infected ticks removed from birds (1.6% MIP), ticks removed from rabbits (5.3% MIP), and rabbit ear biopsies (5%) comprised twelve novel IGS strains. Six species of wild birds were implicated as reservoirs for <it>B. andersonii.</it> Frequency of <it>I. dentatus</it> larval and nymphal co-feeding on birds was ten times greater than expected by chance. The relatively well-studied ecology of <it>I. scapularis</it> and the Lyme disease pathogen provides a context for understanding how the phenology of bird ticks may impact <it>B. miyamotoi</it> and <it>B. andersonii</it> prevalence and host associations.</p> <p>Conclusions</p> <p>Given the current invasion of <it>I. scapularis</it>, a human biting species that serves as a bridge vector for <it>Borrelia</it> spirochetes, human exposure to <it>B. miyamotoi</it> and <it>B. andersonii</it> in this region may increase. The presence of these spirochetes underscores the ecological complexity within which <it>Borrelia</it> organisms are maintained and the need for diagnostic tests to differentiate among these organisms.</p

Different populations of blacklegged tick nymphs exhibit differences in questing behavior that have implications for human lyme disease risk.

Animal behavior can have profound effects on pathogen transmission and disease incidence. We studied the questing (= host-seeking) behavior of blacklegged tick (Ixodes scapularis) nymphs, which are the primary vectors of Lyme disease in the eastern United States. Lyme disease is common in northern but not in southern regions, and prior ecological studies have found that standard methods used to collect host-seeking nymphs in northern regions are unsuccessful in the south. This led us to hypothesize that there are behavior differences between northern and southern nymphs that alter how readily they are collected, and how likely they are to transmit the etiological agent of Lyme disease to humans. To examine this question, we compared the questing behavior of I. scapularis nymphs originating from one northern (Lyme disease endemic) and two southern (non-endemic) US regions at field sites in Wisconsin, Rhode Island, Tennessee, and Florida. Laboratory-raised uninfected nymphs were monitored in circular 0.2 m2 arenas containing wooden dowels (mimicking stems of understory vegetation) for 10 (2011) and 19 (2012) weeks. The probability of observing nymphs questing on these stems (2011), and on stems, on top of leaf litter, and on arena walls (2012) was much greater for northern than for southern origin ticks in both years and at all field sites (19.5 times greater in 2011; 3.6-11.6 times greater in 2012). Our findings suggest that southern origin I. scapularis nymphs rarely emerge from the leaf litter, and consequently are unlikely to contact passing humans. We propose that this difference in questing behavior accounts for observed geographic differences in the efficacy of the standard sampling techniques used to collect questing nymphs. These findings also support our hypothesis that very low Lyme disease incidence in southern states is, in part, a consequence of the type of host-seeking behavior exhibited by southern populations of the key Lyme disease vector