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      Competition Between Strains of Borrelia afzelii in Immature Ixodes ricinus Ticks Is Not Affected by Season


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          Vector-borne pathogens often consist of genetically distinct strains that can establish co-infections in the vertebrate host and the arthropod vector. Co-infections (or mixed infections) can result in competitive interactions between strains with important consequences for strain abundance and transmission. Here we used the spirochete bacterium, Borrelia afzelii, as a model system to investigate the interactions between strains inside its tick vector, Ixodes ricinus. Larvae were fed on mice infected with either one or two strains of B. afzelii. Engorged larvae were allowed to molt into nymphs that were subsequently exposed to three seasonal treatments (artificial summer, artificial winter, and natural winter), which differed in temperature and light conditions. We used strain-specific qPCRs to quantify the presence and abundance of each strain in the immature ticks. Co-infection in the mice reduced host-to-tick transmission to larval ticks and this effect was maintained in the resultant nymphs at 1 and 4 months after the larva-to-nymph molt. Competition between strains in co-infected ticks reduced the abundance of both strains. This inter-strain competition occurred in the three life stages that we investigated: engorged larvae, recently molted nymphs, and overwintered nymphs. The abundance of B. afzelii in the nymphs declined by 40.5% over a period of 3 months, but this phenomenon was not influenced by the seasonal treatment. Future studies should investigate whether inter-strain competition in the tick influences the subsequent strain-specific transmission success from the tick to the vertebrate host.

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          Most cited references72

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          The ecology of genetically diverse infections.

          Microparasite infections often consist of genetically distinct clonal lineages. Ecological interactions between these lineages within hosts can influence disease severity, epidemiology, and evolution. Many medical and veterinary interventions have an impact on genetic diversity within infections, but there is little understanding of the long-term consequences of such interventions for public and animal health. Indeed, much of the theory in this area is based on assumptions contradicted by the available data.
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            Multiple infections and the evolution of virulence.

            Infections that consist of multiple parasite strains or species are common in the wild and are a major public health concern. Theory suggests that these infections have a key influence on the evolution of infectious diseases and, more specifically, on virulence evolution. However, we still lack an overall vision of the empirical support for these predictions. We argue that within-host interactions between parasites largely determine how virulence evolves and that experimental data support model predictions. Then, we explore the main limitation of the experimental study of such 'mixed infections', which is that it draws conclusions on evolutionary outcomes from studies conducted at the individual level. We also discuss differences between coinfections caused by different strains of the same species or by different species. Overall, we argue that it is possible to make sense out of the complexity inherent to multiple infections and that experimental evolution settings may provide the best opportunity to further our understanding of virulence evolution. © 2013 Blackwell Publishing Ltd/CNRS.
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              Fundamental processes in the evolutionary ecology of Lyme borreliosis.

              The evolutionary ecology of many emerging infectious diseases, particularly vector-borne zoonoses, is poorly understood. Here, we aim to develop a biological, process-based framework for vector-borne zoonoses, using Borrelia burgdorferi sensu lato (s.l.), the causative agent of Lyme borreliosis in humans, as an example. We explore the fundamental biological processes that operate in this zoonosis and put forward hypotheses on how extrinsic cues and intrinsic dynamics shape B. burgdorferi s.l. populations. Additionally, we highlight possible epidemiological parallels between B. burgdorferi s.l. and other vector-borne zoonotic pathogens, including West Nile virus.

                Author and article information

                Front Cell Infect Microbiol
                Front Cell Infect Microbiol
                Front. Cell. Infect. Microbiol.
                Frontiers in Cellular and Infection Microbiology
                Frontiers Media S.A.
                19 December 2019
                : 9
                : 431
                [1] 1Laboratory of Ecology and Evolution of Parasites, Institute of Biology, University of Neuchâtel , Neuchâtel, Switzerland
                [2] 2Laboratory of Ecology and Epidemiology of Parasites, Institute of Biology, University of Neuchâtel , Neuchâtel, Switzerland
                [3] 3Department of Veterinary Microbiology, Western College of Veterinary Medicine, University of Saskatchewan , Saskatoon, SK, Canada
                Author notes

                Edited by: Ryan Oliver Marino Rego, Institute of Parasitology (ASCR), Czechia

                Reviewed by: Andrei Daniel Mihalca, University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, Romania; Yi-Pin Lin, Wadsworth Center, United States

                *Correspondence: Dolores Genné dolores.genne@ 123456unine.ch

                This article was submitted to Parasite and Host, a section of the journal Frontiers in Cellular and Infection Microbiology

                Copyright © 2019 Genné, Sarr, Rais and Voordouw.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                : 01 October 2019
                : 04 December 2019
                Page count
                Figures: 4, Tables: 4, Equations: 0, References: 79, Pages: 14, Words: 11687
                Funded by: Schweizerischer Nationalfonds zur F�rderung der Wissenschaftlichen Forschung 10.13039/501100001711
                Cellular and Infection Microbiology
                Original Research

                Infectious disease & Microbiology
                borrelia afzelii,co-infection,inter-strain competition,ixodes ricinus,transmission,vector-borne pathogen,lyme disease


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