The evolving story of Borrelia burgdorferi sensu lato transmission in Europe

Abstract

Beside mosquitoes, ticks are well-known vectors of different human pathogens. In the Northern Hemisphere, Lyme borreliosis (Eurasia, LB) or Lyme disease (North America, LD) is the most commonly occurring vector-borne infectious disease caused by bacteria of the genus Borrelia which are transmitted by hard ticks of the genus Ixodes. The reported incidence of LB in Europe is about 22.6 cases per 100,000 inhabitants annually with a broad range depending on the geographical area analyzed. However, the epidemiological data are largely incomplete, because LB is not notifiable in all European countries. Furthermore, not only differ reporting procedures between countries, there is also variation in case definitions and diagnostic procedures. Lyme borreliosis is caused by several species of the Borrelia (B.) burgdorferi sensu lato (s.l.) complex which are maintained in complex networks including ixodid ticks and different reservoir hosts. Vector and host influence each other and are affected by multiple factors including climate that have a major impact on their habitats and ecology. To classify factors that influence the risk of transmission of B. burgdorferi s.l. to their different vertebrate hosts as well as to humans, we briefly summarize the current knowledge about the pathogens including their astonishing ability to overcome various host immune responses, regarding the main vector in Europe Ixodes ricinus, and the disease caused by borreliae. The research shows, that a higher standardization of case definition, diagnostic procedures, and standardized, long-term surveillance systems across Europe is necessary to improve clinical and epidemiological data.

FtlA and FtlB Are Candidates for Inclusion in a Next-Generation Multiantigen Subunit Vaccine for Lyme Disease

“…We refer to pathogenic Borreliella species collectively as the LD spirochetes. LD spirochetes are maintained in nature in an enzootic cycle involving Ixodes species ticks and diverse vertebrate reservoirs ( 5 , 6 ). The CDC reported in 2016 that Ixodes scapularis and Ixodes pacificus ticks, the primary vectors for LD in North America, are present in 49.2% of United States counties ( 7 ).…”

Environment, animal hosts and human activity on predicting space-time variations of Lyme Borreliosis incidence in France: a Bayesian two-part model

“…12 Anthropogenic data characterizing human outdoor activity or human exposure to infected tick is challenging to collect. 8 Yet, recent citizen science research have shown promising results on characterizing human exposure to tick bite. 13 In addition, large-scale exploration of these above variables in relation to human LB occurrence in a comprehensive framework has not yet been done.…”

“…7 The presence and abundance of infected ticks therefore depend on the distribution of animal hosts, as well as suitable climates and vegetation habitats, allowing host-seeking, molting, and the completion of Ixodes’ life cycle (egg, larvae, nymph and adult). 8 Spillover to humans can occur through the bite of infected ticks, during outdoors activities. Understanding the spatial heterogeneity of LB incidence in humans therefore necessitate to account for environmental, meteorological factors and animal hosts’ distribution that can influence the presence and abundance of infected ticks, as well as humans’ exposure to infectious tick bites.…”

Borrelia Ecology and Evolution: Ticks and Hosts and the Environment

“…Some of these changes are likely to be positive, improving survival conditions for vector and reservoir host, but others may be negative, depleting tick and/or reservoir host populations. These impacts on tick or host abundance, Borrelia infection prevalence in ticks and Borrelia population alterations may result in stable or changing risks for human to acquire the bacteria and to develop LB or RF [ 7 , 10 , 11 , 12 , 13 , 14 , 15 ]. As the human population is growing and space requirements for humans and their habitations are increasing, contact between humans, ticks and borreliae will also increase [ 15 ].…”

“…These impacts on tick or host abundance, Borrelia infection prevalence in ticks and Borrelia population alterations may result in stable or changing risks for human to acquire the bacteria and to develop LB or RF [ 7 , 10 , 11 , 12 , 13 , 14 , 15 ]. As the human population is growing and space requirements for humans and their habitations are increasing, contact between humans, ticks and borreliae will also increase [ 15 ]. There are still many open questions that need to be addressed surrounding this complex system.…”