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"Lyme disease Environmental aspects."
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Lyme disease : the ecology of a complex system
A synthetic review of research on the ecology of Lyme disease in North America.
Book
Lyme borreliosis
Lyme borreliosis (Lyme disease) is caused by spirochaetes of the Borrelia burgdorferi sensu lato species complex, which are transmitted by ticks. The most common clinical manifestation is erythema migrans, which eventually resolves, even without antibiotic treatment. However, the infecting pathogen can spread to other tissues and organs, causing more severe manifestations that can involve a patient's skin, nervous system, joints, or heart. The incidence of this disease is increasing in many countries. Laboratory evidence of infection, mainly serology, is essential for diagnosis, except in the case of typical erythema migrans. Diagnosed cases are usually treated with antibiotics for 2–4 weeks and most patients make an uneventful recovery. No convincing evidence exists to support the use of antibiotics for longer than 4 weeks, or for the persistence of spirochaetes in adequately treated patients. Prevention is mainly accomplished by protecting against tick bites. There is no vaccine available for human beings.
Journal Article
Interactions between Borrelia burgdorferi and ticks
Borrelia burgdorferi is the causative agent of Lyme disease and is transmitted to vertebrate hosts by Ixodes spp. ticks. The spirochaete relies heavily on its arthropod host for basic metabolic functions and has developed complex interactions with ticks to successfully colonize, persist and, at the optimal time, exit the tick. For example, proteins shield spirochaetes from immune factors in the bloodmeal and facilitate the transition between vertebrate and arthropod environments. On infection, B. burgdorferi induces selected tick proteins that modulate the vector gut microbiota towards an environment that favours colonization by the spirochaete. Additionally, the recent sequencing of the Ixodes scapularis genome and characterization of tick immune defence pathways, such as the JAK–STAT, immune deficiency and cross-species interferon-γ pathways, have advanced our understanding of factors that are important for B. burgdorferi persistence in the tick. In this Review, we summarize interactions between B. burgdorferi and I. scapularis during infection, as well as interactions with tick gut and salivary gland proteins important for establishing infection and transmission to the vertebrate host.Borrelia burgdorferi has a complex life cycle with several different hosts, causing Lyme disease when it infects humans. In this Review, Fikrig and colleagues discuss how B. burgdorferi infects and interacts with its tick vector to ensure onward transmission.
Journal Article
Effects of Tick-Control Interventions on Tick Abundance, Human Encounters with Ticks, and Incidence of Tickborne Diseases in Residential Neighborhoods, New York, USA
Tickborne diseases (TBDs) such as Lyme disease result in ≈500,000 diagnoses annually in the United States. Various methods can reduce the abundance of ticks at small spatial scales, but whether these methods lower incidence of TBDs is poorly understood. We conducted a randomized, replicated, fully crossed, placebo-controlled, masked experiment to test whether 2 environmentally safe interventions, the Tick Control System (TCS) and Met52 fungal spray, used separately or together, affected risk for and incidence of TBDs in humans and pets in 24 residential neighborhoods. All participating properties in a neighborhood received the same treatment. TCS was associated with fewer questing ticks and fewer ticks feeding on rodents. The interventions did not result in a significant difference in incidence of human TBDs but did significantly reduce incidence in pets. Our study is consistent with previous evidence suggesting that reducing tick abundance in residential areas might not reduce incidence of TBDs in humans.
Journal Article
Determinants of vector-borne avian pathogen occurrence in a mosaic of habitat fragmentation in California
Background
As habitat fragmentation increases, ecological processes, including patterns of vector-borne pathogen prevalence, will likely be disrupted, but ongoing investigations are necessary to examine this relationship. Here, we report the differences in the prevalence of Lyme disease (
Borrelia burgdorferi
sensu lato, s.l.) and haemoproteosis (
Haemoproteus
spp.) pathogens in avian populations of a fragmented habitat.
B. burgdorferi
s.l. is a generalist pathogen that is transmitted by
Ixodes pacificus
vectors in California, and
Haemoproteus
is an avian parasite transmitted by
Culicoides
vectors.
Methods
To determine whether biotic (avian and mammalian abundance) or abiotic characteristics (patch size and water availability) correlated with infection prevalence change, we screened 176 birds sampled across seven sites in oak woodland habitat in northern California.
Results
While biotic factors correlated with an increase in both pathogens, infection prevalence of
Haemoproteus
spp. was only associated with individual-level traits, specifically foraging substrate and diet, and
B. burgdorferi
s.l. was associated with community-level characteristics, both total mammal and, specifically, rodent abundance. Proximity to water was the only abiotic factor found to be significant for both pathogens and reinforces the importance of water availability for transmission cycles. Larger patch sizes did not significantly affect infection prevalence of
Haemoproteus,
but did increase the prevalence of
B. burgdorferi.
Conclusions
These results highlight that while environmental factors (specifically habitat fragmentation) have a limited role in vector-borne pathogen prevalence, the indirect impact to biotic factors (community composition) can have consequences for both
Haemoproteus
and
B. burgdorferi
prevalence in birds. Given the pervasiveness of habitat fragmentation, our results are of broad significance.
Graphical abstract
Journal Article
Estimated Effects of Projected Climate Change on the Basic Reproductive Number of the Lyme Disease Vector Ixodes scapularis
The extent to which climate change may affect human health by increasing risk from vector-borne diseases has been under considerable debate.
We quantified potential effects of future climate change on the basic reproduction number (R0) of the tick vector of Lyme disease, Ixodes scapularis, and explored their importance for Lyme disease risk, and for vector-borne diseases in general.
We applied observed temperature data for North America and projected temperatures using regional climate models to drive an I. scapularis population model to hindcast recent, and project future, effects of climate warming on R0. Modeled R0 increases were compared with R0 ranges for pathogens and parasites associated with variations in key ecological and epidemiological factors (obtained by literature review) to assess their epidemiological importance.
R0 for I. scapularis in North America increased during the years 1971-2010 in spatio-temporal patterns consistent with observations. Increased temperatures due to projected climate change increased R0 by factors (2-5 times in Canada and 1.5-2 times in the United States), comparable to observed ranges of R0 for pathogens and parasites due to variations in strains, geographic locations, epidemics, host and vector densities, and control efforts.
Climate warming may have co-driven the emergence of Lyme disease in northeastern North America, and in the future may drive substantial disease spread into new geographic regions and increase tick-borne disease risk where climate is currently suitable. Our findings highlight the potential for climate change to have profound effects on vectors and vector-borne diseases, and the need to refocus efforts to understand these effects.
Journal Article
Masting by beech trees predicts the risk of Lyme disease
Background
The incidence of Lyme borreliosis and other tick-borne diseases is increasing in Europe and North America. There is currently much interest in identifying the ecological factors that determine the density of infected ticks as this variable determines the risk of Lyme borreliosis to vertebrate hosts, including humans. Lyme borreliosis is caused by the bacterium
Borrelia burgdorferi
sensu lato (s.l.) and in western Europe, the hard tick
Ixodes ricinus
is the most important vector.
Methods
Over a 15-year period (2004–2018), we monitored the monthly abundance of
I. ricinus
ticks (nymphs and adults) and their
B. burgdorferi
s.l. infection status at four different elevations on a mountain in western Switzerland. We collected climate variables in the field and from nearby weather stations. We obtained data on beech tree seed production (masting) from the literature, as the abundance of
Ixodes
nymphs can increase dramatically 2 years after a masting event. We used generalized linear mixed effects models and AIC-based model selection to identify the ecological factors that influence inter-annual variation in the nymphal infection prevalence (NIP) and the density of infected nymphs (DIN).
Results
We found that the NIP decreased by 78% over the study period. Inter-annual variation in the NIP was explained by the mean precipitation in the present year, and the duration that the DNA extraction was stored in the freezer prior to pathogen detection. The DIN decreased over the study period at all four elevation sites, and the decrease was significant at the top elevation. Inter-annual variation in the DIN was best explained by elevation site, year, beech tree masting index 2 years prior and the mean relative humidity in the present year. This is the first study in Europe to demonstrate that seed production by deciduous trees influences the density of nymphs infected with
B. burgdorferi
s.l. and hence the risk of Lyme borreliosis.
Conclusions
Public health officials in Europe should be aware that masting by deciduous trees is an important predictor of the risk of Lyme borreliosis.
Graphical Abstract
Journal Article
A systematic review of the effectiveness and utility of Lyme disease prevention measures in Canada, the United States, and Europe
Background
This systematic review aimed to assess the effectiveness of interventions which reduce human-tick encounters, prevent tick bites, and reduce the risk of
Borrelia burgdorferi
transmission, and to evaluate knowledge on the cost, environmental impact, social impact and acceptability, and public health impact of these interventions.
Methods
The search was conducted in Medline, Embase, Global Health, CAB Abstracts, Cochrane CENTRAL, Scopus, and Econlit for relevant literature in March 2022 and was updated in November 2024 and followed PRISMA guidelines for systematic reviews. Inclusion was applied at citation and full text, after which articles were assessed for risk of bias and data was extracted by two independent reviewers. Studies were summarized by intervention type (landscape management, host animal parasitism and movement, chemical/natural/botanical applications, personal protection) and a multi-study synthesis of tick suppression effects was conducted for interventions that reported the density of infected nymphs as the primary outcome.
Results
One hundred and twenty-seven studies published between 1977 and 2024 were included in this systematic review. Most studies (
n
= 62) were classified as host-targeted interventions. Twenty-five studies were included in the multi-study synthesis of tick suppression effects, which suggested that chemical tick control methods are the most effective and consistent intervention type with 93.8% mean suppression of questing nymphs.
Conclusion
While some strategies such as chemical acaricides were shown to have greater effectiveness, factors such as social acceptability and resistance, environmental impact, cost, and feasibility should be considered when selecting the most appropriate intervention to maximize the utility of the intervention.
Journal Article
Lyme Disease Risks in Europe under Multiple Uncertain Drivers of Change
Debates over whether climate change could lead to the amplification of Lyme disease (LD) risk in the future have received much attention. Although recent large-scale disease mapping studies project an overall increase in Lyme disease risk as the climate warms, such conclusions are based on climate-driven models in which other drivers of change, such as land-use/cover and host population distribution, are less considered.
The main objectives were to project the likely future ecological risk patterns of LD in Europe under different assumptions about future socioeconomic and climate conditions and to explore similarity and uncertainty in the projected risks.
An integrative, spatially explicit modeling study of the ecological risk patterns of LD in Europe was conducted by applying recent advances in process-based modeling of tick-borne diseases, species distribution mapping, and scenarios of land-use/cover change. We drove the model with stakeholder-driven, integrated scenarios of plausible future socioeconomic and climate change [the Shared Socioeconomic Pathway (SSPs) combined with the Representative Concentration Pathways (RCPs)].
The model projections suggest that future temperature increases may not always amplify LD risk: Low emissions scenarios (RCP2.6) combined with a sustainability socioeconomic scenario (SSP1) resulted in reduced LD risk. The greatest increase in risk was projected under intermediate (RCP4.5) rather than high-end (RCP8.5) climate change scenarios. Climate and land-use change were projected to have different roles in shaping the future regional dynamics of risk, with climate warming being likely to cause risk expansion in northern Europe and conversion of forest to agriculture being likely to limit risk in southern Europe.
Projected regional differences in LD risk resulted from mixed effects of temperature, land use, and host distributions, suggesting region-specific and cross-sectoral foci for LD risk management policy. The integrated model provides an improved explanatory tool for the system mechanisms of LD pathogen transmission and how pathogen transmission could respond to combined socioeconomic and climate changes. https://doi.org/10.1289/EHP4615.
Journal Article
Factors influencing Lyme borreliosis risk perception in Europe: a cross-sectional multi-country survey study
Background
Lyme borreliosis (LB) is the most common vector-borne disease in Europe. Research on factors that shape LB risk perception in Europe is limited. This study explores the potential drivers of LB risk perception in the general adult (18–65 years) population of twenty European countries, such as urbanicity, socioeconomic status, dog ownership, gender, age, and tick and LB diagnosis history.
Methods
Data were obtained from a 2022 survey of 28,034 adults aged 18–65 years in twenty European countries. The survey included questions on knowledge, attitudes, and practices related to ticks and LB. Respondents were categorized into three income levels (low, middle, or high) based on country-specific income tertiles. Descriptive statistics were calculated, and differences in responses to survey items by income level were assessed using chi-square tests. Risk perception was measured from a survey question asking respondents to rate their risk of contracting LB on a five-point scale from “very low risk” to “very high risk.” Ordinal logistic regression modeled the relationship between predictor variables and LB risk perception.
Results
Having a past LB diagnosis (adjusted odds ratio [AOR]: 3.96, 95% confidence interval [CI]: 3.38–4.64) was most strongly tied to increased LB risk perception. Knowing someone with a past LB diagnosis or having a past tick bite, were also significantly associated with higher risk perception (AOR: 2.11, 95% CI: 1.97–2.27, and AOR: 1.71, 95% CI: 1.60–1.84, respectively). High-income respondents were most likely to report a past tick bite (55.4%, 95% CI: 53.5–57.3%) and a past LB diagnosis (13.5%, 95% CI: 12.1–14.8%).
Conclusions
Experience with ticks and LB (i.e., via bites or diagnoses) may play a key role in shaping LB risk perception among European adults. Dog ownership and demographic factors such as gender and age may also influence LB risk perception. These results could help LB educational campaigns addressing knowledge and perception gaps.
Journal Article