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Le virus Kemerovo, un orbivirus encéphalitique transmis par les tiques : études in vivo et in vitro

Abstract : Ticks represent a major risk to human and animal health and are responsible forimportant economic losses. It is the principal vector of pathogens in Europe and can transmit the widest variety of microorganisms (bacteria, parasites and viruses). Among these, about 170 tick-borne viruses have been identified to date. These viruses are arboviruses (arthropod-borne viruses) transmitted by hematophagous arthropod vectors such as ticks, mosquitoes, sandflies and biting midges. Complex interactions define the relationships between arboviruses and their vectors. The ability of an arthropod to transmit a virus is defined by its vector competence. The arthropod must ingest the virusduring a blood meal on infected vertebrate hosts and replicate it, and further transmit it to other hosts during the next blood meal. Arboviruses replicate within an arthropod vector and a vertebrate host. Animal arboviruses are mainly RNA viruses and have high mutation rates compared to DNA viruses. These mutations are mainly due to a lack of proofreading properties of their RNA-dependent RNA polymerase. Their life cycle within 2 very different hosts would lead to the fixation of beneficial mutations for infection and replication in these hosts. Arboviruses have a great capacity to generate variants (quasispecies) that are able to explore new environments and facilitate viral emergence.However, the genomic variability of insect-borne viruses has been extensively studied and host alternation could constrain arbovirus evolution. This hypothesis was then extrapolated to all arboviruses, including tick-borne viruses. However, ticks and insects have different life cycles and traits and the viruses are not subject to the same pressures.In this context, this PhD project was devised to study the interactions betweenKemerovo virus (KEMV) and its tick vectors at different levels. KEMV is an orbivirus discovered in 1962 in the Kemerovo region. KEMv and its two serotypes Tribeč (TRBV) and Lipovnik (LIPV)have all three been implicated in human cases of encephalitis in Russia and/or Central Europe. However, the interest in KEMV has declined in favour of the diagnosis of tick-borne encephalitis virus (TBEV) in these regions.The studies conducted during this thesis pertained to in vivo and in vitro models. First, the vector competence of Ixodes ricinus and Ixodes persulcatus ticks was studied. This work involved setting up a tick infection model with KEMV in the laboratory. The different criteria of vector competence were then tested for I. ricinus and I. persulcatus. In the course of this study, we were able to highlight the influence of (1) the virus genus on the infection technique used and (2) the species and origin of the ticks when testing vector competence.Finally, the second part of this work was the study of the influence of hostalternation on fitness, virulence and tropism of KEMV in an animal model. KEMV was adapted in cell culture according to 3 scenarii : 30 serial passages in mammalian or tick cells or alternated passages between the 2 cell types. For that purpose, it was necessary to collect information on KEMV biology in order to set up the different passages. The fitness of the different cell-adapted strains was studied in our animal model, the IFNAR-/- mouse, as well as the virulence. We were able to show a link between the virulence of the adapted strains and the sex and age of the mice, suggesting the selection of quasispecies during different passages.
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Camille Migné. Le virus Kemerovo, un orbivirus encéphalitique transmis par les tiques : études in vivo et in vitro. Microbiologie et Parasitologie. AgroParisTech, 2022. Français. ⟨NNT : 2022AGPT0002⟩. ⟨tel-03762291⟩

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