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Mansfield KL, Schilling M, Sanders C, Holding M, Johnson N. Arthropod-Borne Viruses of Human and Animal Importance: Overwintering in Temperate Regions of Europe during an Era of Climate Change. Microorganisms 2024; 12:1307. [PMID: 39065076 PMCID: PMC11278640 DOI: 10.3390/microorganisms12071307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2024] [Revised: 06/20/2024] [Accepted: 06/22/2024] [Indexed: 07/28/2024] Open
Abstract
The past three decades have seen an increasing number of emerging arthropod-borne viruses in temperate regions This process is ongoing, driven by human activities such as inter-continental travel, combined with the parallel emergence of invasive arthropods and an underlying change in climate that can increase the risk of virus transmission and persistence. In addition, natural events such as bird migration can introduce viruses to new regions. Despite the apparent regularity of virus emergence, arthropod-borne viruses circulating in temperate regions face the challenge of the late autumn and winter months where the arthropod vector is inactive. Viruses therefore need mechanisms to overwinter or they will fail to establish in temperate zones. Prolonged survival of arthropod-borne viruses within the environment, outside of both vertebrate host and arthropod vector, is not thought to occur and therefore is unlikely to contribute to overwintering in temperate zones. One potential mechanism is continued infection of a vertebrate host. However, infection is generally acute, with the host either dying or producing an effective immune response that rapidly clears the virus. There are few exceptions to this, although prolonged infection associated with orbiviruses such as bluetongue virus occurs in certain mammals, and viraemic vertebrate hosts therefore can, in certain circumstances, provide a route for long-term viral persistence in the absence of active vectors. Alternatively, a virus can persist in the arthropod vector as a mechanism for overwintering. However, this is entirely dependent on the ecology of the vector itself and can be influenced by changes in the climate during the winter months. This review considers the mechanisms for virus overwintering in several key arthropod vectors in temperate areas. We also consider how this will be influenced in a warming climate.
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Affiliation(s)
- Karen L. Mansfield
- Vector Borne Diseases, Virology Department, Animal and Plant Health Agency, Woodham Lane, Addlestone, Surrey KT15 3NB, UK; (K.L.M.); (M.S.)
| | - Mirjam Schilling
- Vector Borne Diseases, Virology Department, Animal and Plant Health Agency, Woodham Lane, Addlestone, Surrey KT15 3NB, UK; (K.L.M.); (M.S.)
| | | | - Maya Holding
- Virology and Pathogenesis Group, UK Health Security Agency, Porton Down, Salisbury SP4 0JG, UK;
| | - Nicholas Johnson
- Vector Borne Diseases, Virology Department, Animal and Plant Health Agency, Woodham Lane, Addlestone, Surrey KT15 3NB, UK; (K.L.M.); (M.S.)
- Faculty of Health and Medical Sciences, University of Surrey, Guildford GU2 7XH, UK
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Simkute E, Pautienius A, Grigas J, Sidorenko M, Radzijevskaja J, Paulauskas A, Stankevicius A. The Prevalence of Tick-Borne Encephalitis Virus in Wild Rodents Captured in Tick-Borne Encephalitis Foci in Highly Endemic Lithuania. Viruses 2024; 16:444. [PMID: 38543809 PMCID: PMC10974453 DOI: 10.3390/v16030444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2024] [Revised: 03/10/2024] [Accepted: 03/11/2024] [Indexed: 05/23/2024] Open
Abstract
Wild rodents are considered to be one of the most important TBEV-amplifying reservoir hosts; therefore, they may be suitable for foci detection studies. To investigate the effectiveness of viral RNA detection in wild rodents for suspected TBEV foci confirmation, we trapped small rodents (n = 139) in various locations in Lithuania where TBEV was previously detected in questing ticks. Murine neuroblastoma Neuro-2a cells were inoculated with each rodent sample to maximize the chances of detecting viral RNA in rodent samples. TBEV RNA was detected in 74.8% (CI 95% 66.7-81.1) of the brain and/or internal organ mix suspensions, and the prevalence rate increased significantly following sample cultivation in Neuro-2a cells. Moreover, a strong correlation (r = 0.88; p < 0.05) was found between the average monthly air temperature of rodent trapping and the TBEV RNA prevalence rate in cell culture isolates of rodent suspensions, which were PCR-negative before cultivation in cell culture. This study shows that wild rodents are suitable sentinel animals to confirm TBEV foci. In addition, the study results demonstrate that sample cultivation in cell culture is a highly efficient method for increasing TBEV viral load to detectable quantities.
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Affiliation(s)
- Evelina Simkute
- Laboratory of Immunology, Department of Anatomy and Physiology, Lithuanian University of Health Sciences, Tilzes Str. 18, LT-47181 Kaunas, Lithuania; (A.P.); (J.G.); (A.S.)
| | - Arnoldas Pautienius
- Laboratory of Immunology, Department of Anatomy and Physiology, Lithuanian University of Health Sciences, Tilzes Str. 18, LT-47181 Kaunas, Lithuania; (A.P.); (J.G.); (A.S.)
- Institute of Microbiology and Virology, Lithuanian University of Health Sciences, Tilzes Str. 18, LT-47181 Kaunas, Lithuania
| | - Juozas Grigas
- Laboratory of Immunology, Department of Anatomy and Physiology, Lithuanian University of Health Sciences, Tilzes Str. 18, LT-47181 Kaunas, Lithuania; (A.P.); (J.G.); (A.S.)
- Institute of Microbiology and Virology, Lithuanian University of Health Sciences, Tilzes Str. 18, LT-47181 Kaunas, Lithuania
| | - Marina Sidorenko
- Department of Biology, Faculty of Natural Sciences, Vytautas Magnus University, K. Donelaicio Str. 58, LT-44248 Kaunas, Lithuania; (M.S.); (J.R.); (A.P.)
| | - Jana Radzijevskaja
- Department of Biology, Faculty of Natural Sciences, Vytautas Magnus University, K. Donelaicio Str. 58, LT-44248 Kaunas, Lithuania; (M.S.); (J.R.); (A.P.)
| | - Algimantas Paulauskas
- Department of Biology, Faculty of Natural Sciences, Vytautas Magnus University, K. Donelaicio Str. 58, LT-44248 Kaunas, Lithuania; (M.S.); (J.R.); (A.P.)
| | - Arunas Stankevicius
- Laboratory of Immunology, Department of Anatomy and Physiology, Lithuanian University of Health Sciences, Tilzes Str. 18, LT-47181 Kaunas, Lithuania; (A.P.); (J.G.); (A.S.)
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Jaenson TGT, Petersson EH, Jaenson DGE, Kindberg J, Pettersson JHO, Hjertqvist M, Medlock JM, Bengtsson H. The importance of wildlife in the ecology and epidemiology of the TBE virus in Sweden: incidence of human TBE correlates with abundance of deer and hares. Parasit Vectors 2018; 11:477. [PMID: 30153856 PMCID: PMC6114827 DOI: 10.1186/s13071-018-3057-4] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Accepted: 08/10/2018] [Indexed: 02/06/2023] Open
Abstract
Background Tick-borne encephalitis (TBE) is one tick-transmitted disease where the human incidence has increased in some European regions during the last two decades. We aim to find the most important factors causing the increasing incidence of human TBE in Sweden. Based on a review of published data we presume that certain temperature-related variables and the population densities of transmission hosts, i.e. small mammals, and of primary tick maintenance hosts, i.e. cervids and lagomorphs, of the TBE virus vector Ixodes ricinus, are among the potentially most important factors affecting the TBE incidence. Therefore, we compare hunting data of the major tick maintenance hosts and two of their important predators, and four climatic variables with the annual numbers of human cases of neuroinvasive TBE. Data for six Swedish regions where human TBE incidence is high or has recently increased are examined by a time-series analysis. Results from the six regions are combined using a meta-analytical method. Results With a one-year time lag, the roe deer (Capreolus capreolus), red deer (Cervus elaphus), mountain hare (Lepus timidus) and European hare (Lepus europaeus) showed positive covariance; the Eurasian elk (moose, Alces alces) and fallow deer (Dama dama) negative covariance; whereas the wild boar (Sus scrofa), lynx (Lynx lynx), red fox (Vulpes vulpes) and the four climate parameters showed no significant covariance with TBE incidence. All game species combined showed positive covariance. Conclusions The epidemiology of TBE varies with time and geography and depends on numerous factors, i.a. climate, virus genotypes, and densities of vectors, tick maintenance hosts and transmission hosts. This study suggests that the increased availability of deer to I. ricinus over large areas of potential tick habitats in southern Sweden increased the density and range of I. ricinus and created new TBEV foci, which resulted in increased incidence of human TBE. New foci may be established by TBE virus-infected birds, or by birds or migrating mammals infested with TBEV-infected ticks. Generally, persistence of TBE virus foci appears to require presence of transmission-competent small mammals, especially mice (Apodemus spp.) or bank voles (Myodes glareolus). Electronic supplementary material The online version of this article (10.1186/s13071-018-3057-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Thomas G T Jaenson
- Department of Organismal Biology, Uppsala University, Norbyvägen 18d, SE-752 36, Uppsala, Sweden.
| | - Erik H Petersson
- Department of Aquatic Resources, Division of Freshwater Research, Swedish University of Agricultural Sciences, Stångholmsvägen 2, SE-178 93, Drottningholm, Sweden
| | - David G E Jaenson
- Department of Automatic Control, Lund University, SE-221 00, Lund, Sweden
| | - Jonas Kindberg
- Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden
| | - John H-O Pettersson
- Department of Infectious Disease Epidemiology and Modelling, Norwegian Institute of Public Health, Lovisenberggata 8, N-0456, Oslo, Norway.,Department of Medical Biochemistry and Microbiology (IMBIM), Zoonosis Science Center, Uppsala University, Uppsala, Sweden.,Marie Bashir Institute for Infectious Diseases and Biosecurity, Charles Perkins Centre, School of Life and Environmental Sciences and Sydney Medical School, the University of Sydney, Sydney, New South Wales, 2006, Australia.,Public Health Agency of Sweden, Nobels väg 18, SE-171 82, Solna, Sweden
| | - Marika Hjertqvist
- Public Health Agency of Sweden, Nobels väg 18, SE-171 82, Solna, Sweden
| | - Jolyon M Medlock
- Medical Entomology Group, Emergency Response Department, Public Health England, Porton Down, Salisbury, UK.,Health Protection Research Unit in Emerging Infections & Zoonoses, Porton Down, Salisbury, UK
| | - Hans Bengtsson
- Swedish Meteorological and Hydrological Institute (SMHI), Gothenburg, Sweden
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The role of the poly(A) tract in the replication and virulence of tick-borne encephalitis virus. Sci Rep 2016; 6:39265. [PMID: 27982069 PMCID: PMC5159820 DOI: 10.1038/srep39265] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Accepted: 11/21/2016] [Indexed: 12/11/2022] Open
Abstract
The tick-borne encephalitis virus (TBEV) is a flavivirus transmitted to humans, usually via tick bites. The virus causes tick-borne encephalitis (TBE) in humans, and symptoms range from mild flu-like symptoms to severe and long-lasting sequelae, including permanent brain damage. It has been suggested that within the population of viruses transmitted to the mammalian host, quasispecies with neurotropic properties might become dominant in the host resulting in neurological symptoms. We previously demonstrated the existence of TBEV variants with variable poly(A) tracts within a single blood-fed tick. To characterize the role of the poly(A) tract in TBEV replication and virulence, we generated infectious clones of Torö-2003 with the wild-type (A)3C(A)6 sequence (Torö-6A) or with a modified (A)3C(A)38 sequence (Torö-38A). Torö-38A replicated poorly compared to Torö-6A in cell culture, but Torö-38A was more virulent than Torö-6A in a mouse model of TBE. Next-generation sequencing of TBEV genomes after passaging in cell culture and/or mouse brain revealed mutations in specific genomic regions and the presence of quasispecies that might contribute to the observed differences in virulence. These data suggest a role for quasispecies development within the poly(A) tract as a virulence determinant for TBEV in mice.
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Bernardi Schneider A, Malone RW, Guo J, Homan J, Linchangco G, Witter ZL, Vinesett D, Damodaran L, Janies DA. Molecular evolution of Zika virus as it crossed the Pacific to the Americas. Cladistics 2016; 33:1-20. [DOI: 10.1111/cla.12178] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/20/2016] [Indexed: 01/10/2023] Open
Affiliation(s)
- Adriano Bernardi Schneider
- Department of Bioinformatics and Genomics University of North Carolina at Charlotte 9201 University City Blvd Charlotte 28223‐0001 NC USA
| | - Robert W. Malone
- Atheric Pharmaceutical 2981 Zion Road Troy VA 22974 USA
- Class of 2016 Harvard Medical School Global Clinical Scholars Research Training Program Boston MA USA
| | - Jun‐Tao Guo
- Department of Bioinformatics and Genomics University of North Carolina at Charlotte 9201 University City Blvd Charlotte 28223‐0001 NC USA
| | - Jane Homan
- ioGenetics LLC 3591 Anderson Street, Suite 218 Madison WI 53704 USA
| | - Gregorio Linchangco
- Department of Bioinformatics and Genomics University of North Carolina at Charlotte 9201 University City Blvd Charlotte 28223‐0001 NC USA
| | - Zachary L. Witter
- Department of Bioinformatics and Genomics University of North Carolina at Charlotte 9201 University City Blvd Charlotte 28223‐0001 NC USA
| | - Dylan Vinesett
- Department of Bioinformatics and Genomics University of North Carolina at Charlotte 9201 University City Blvd Charlotte 28223‐0001 NC USA
| | - Lambodhar Damodaran
- Department of Bioinformatics and Genomics University of North Carolina at Charlotte 9201 University City Blvd Charlotte 28223‐0001 NC USA
| | - Daniel A. Janies
- Department of Bioinformatics and Genomics University of North Carolina at Charlotte 9201 University City Blvd Charlotte 28223‐0001 NC USA
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Asghar N, Lindblom P, Melik W, Lindqvist R, Haglund M, Forsberg P, Överby AK, Andreassen Å, Lindgren PE, Johansson M. Tick-borne encephalitis virus sequenced directly from questing and blood-feeding ticks reveals quasispecies variance. PLoS One 2014; 9:e103264. [PMID: 25058476 PMCID: PMC4110009 DOI: 10.1371/journal.pone.0103264] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Accepted: 06/25/2014] [Indexed: 01/10/2023] Open
Abstract
The increased distribution of the tick-borne encephalitis virus (TBEV) in Scandinavia highlights the importance of characterizing novel sequences within the natural foci. In this study, two TBEV strains: the Norwegian Mandal 2009 (questing nymphs pool) and the Swedish Saringe 2009 (blood-fed nymph) were sequenced and phylogenetically characterized. Interestingly, the sequence of Mandal 2009 revealed the shorter form of the TBEV genome, similar to the highly virulent Hypr strain, within the 3′ non-coding region (3′NCR). A different genomic structure was found in the 3′NCR of Saringe 2009, as in-depth analysis demonstrated TBEV variants with different lengths within the poly(A) tract. This shows that TBEV quasispecies exists in nature and indicates a putative shift in the quasispecies pool when the virus switches between invertebrate and vertebrate environments. This prompted us to further sequence and analyze the 3′NCRs of additional Scandinavian TBEV strains and control strains, Hypr and Neudoerfl. Toro 2003 and Habo 2011 contained mainly a short (A)3C(A)6 poly(A) tract. A similar pattern was observed for the human TBEV isolates 1993/783 and 1991/4944; however, one clone of 1991/4944 contained an (A)3C(A)11 poly(A) sequence, demonstrating that quasispecies with longer poly(A) could be present in human isolates. Neudoerfl has previously been reported to contain a poly(A) region, but to our surprise the re-sequenced genome contained two major quasispecies variants, both lacking the poly(A) tract. We speculate that the observed differences are important factors for the understanding of virulence, spread, and control of the TBEV.
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Affiliation(s)
- Naveed Asghar
- School of Natural Science, Technology & Environmental Studies, Södertörn University, Huddinge, Sweden
| | - Pontus Lindblom
- Division of Medical Microbiology, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
| | - Wessam Melik
- School of Natural Science, Technology & Environmental Studies, Södertörn University, Huddinge, Sweden
| | - Richard Lindqvist
- Department of Clinical Microbiology, Virology, Umeå University, Umeå, Sweden
| | - Mats Haglund
- Department of Infectious Diseases, County Hospital, Kalmar, Sweden
| | - Pia Forsberg
- Division of Infectious Diseases, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
- Clinic of Infectious Diseases, Linköping University Hospital, Linköping, Sweden
| | - Anna K. Överby
- Department of Clinical Microbiology, Virology, Umeå University, Umeå, Sweden
| | - Åshild Andreassen
- Division of Infectious Disease Control, Department of Virology, Norwegian Institute of Public Health, Oslo, Norway
| | - Per-Eric Lindgren
- Division of Medical Microbiology, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
- Division of Medical Services, Department of Microbiology, County Hospital Ryhov, Jönköping, Sweden
| | - Magnus Johansson
- School of Natural Science, Technology & Environmental Studies, Södertörn University, Huddinge, Sweden
- School of Medicine, Örebro University, Örebro, Sweden
- iRiSC - Inflammatory Response and Infection Susceptibility Centre, Faculty of Medicine and Health, Örebro University, Örebro, Sweden
- * E-mail:
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Mlera L, Melik W, Bloom ME. The role of viral persistence in flavivirus biology. Pathog Dis 2014; 71:137-63. [PMID: 24737600 PMCID: PMC4154581 DOI: 10.1111/2049-632x.12178] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Revised: 04/08/2014] [Accepted: 04/09/2014] [Indexed: 12/30/2022] Open
Abstract
In nature, vector borne flaviviruses are persistently cycled between either the tick or mosquito vector and small mammals such as rodents, skunks, and swine. These viruses account for considerable human morbidity and mortality worldwide. Increasing and substantial evidence of viral persistence in humans, which includes the isolation of RNA by RT PCR and infectious virus by culture, continues to be reported. Viral persistence can also be established in vitro in various human, animal, arachnid, and insect cell lines in culture. Although some research has focused on the potential roles of defective virus particles, evasion of the immune response through the manipulation of autophagy and/or apoptosis, the precise mechanism of flavivirus persistence is still not well understood. We propose additional research for further understanding of how viral persistence is established in different systems. Avenues for additional studies include determining whether the multifunctional flavivirus protein NS5 has a role in viral persistence, the development of relevant animal models of viral persistence, and investigating the host responses that allow vector borne flavivirus replication without detrimental effects on infected cells. Such studies might shed more light on the viral–host relationships and could be used to unravel the mechanisms for establishment of persistence. Persistent infections by vector borne flaviviruses are an important, but inadequately studied topic.
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Affiliation(s)
- Luwanika Mlera
- Rocky Mountain Laboratories, Laboratory of Virology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
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8
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Lindblom P, Wilhelmsson P, Fryland L, Sjöwall J, Haglund M, Matussek A, Ernerudh J, Vene S, Nyman D, Andreassen A, Forsberg P, Lindgren PE. Tick-borne encephalitis virus in ticks detached from humans and follow-up of serological and clinical response. Ticks Tick Borne Dis 2013; 5:21-8. [PMID: 24275477 DOI: 10.1016/j.ttbdis.2013.07.009] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Accepted: 07/14/2013] [Indexed: 12/20/2022]
Abstract
The risk of tick-borne encephalitis virus (TBEV) infection after a tick bite remains largely unknown. To address this, we investigated the presence of TBEV in ticks detached from humans in an attempt to relate viral copy number, TBEV subtype, and tick feeding time with the serological and clinical response of the tick-bitten participants. Ticks, blood samples, and questionnaires were collected from tick-bitten humans at 34 primary health care centers in Sweden and in the Åland Islands (Finland). A total of 2167 ticks was received from 1886 persons in 2008-2009. Using a multiplex quantitative real-time PCR, 5 TBEV-infected ticks were found (overall prevalence 0.23%, copy range <4×10(2)-7.7×10(6)per tick). One unvaccinated person bitten by a tick containing 7.7×10(6) TBEV copies experienced symptoms. Another unvaccinated person bitten by a tick containing 1.8×10(3) TBEV copies developed neither symptoms nor TBEV antibodies. The remaining 3 persons were protected by vaccination. In contrast, despite lack of TBEV in the detached ticks, 2 persons developed antibodies against TBEV, one of whom reported symptoms. Overall, a low risk of TBEV infection was observed, and too few persons got bitten by TBEV-infected ticks to draw certain conclusions regarding the clinical outcome in relation to the duration of the blood meal and virus copy number. However, this study indicates that an antibody response may develop without clinical symptoms, that a bite by an infected tick not always leads to an antibody response or clinical symptoms, and a possible correlation between virus load and tick feeding time.
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Affiliation(s)
- Pontus Lindblom
- Division of Medical Microbiology, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden.
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Frey S, Essbauer S, Zöller G, Klempa B, Dobler G, Pfeffer M. Full genome sequences and preliminary molecular characterization of three tick-borne encephalitis virus strains isolated from ticks and a bank vole in Slovak Republic. Virus Genes 2013; 48:184-8. [DOI: 10.1007/s11262-013-0985-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 09/17/2013] [Indexed: 12/17/2022]
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10
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Chursov A, Kopetzky SJ, Leshchiner I, Kondofersky I, Theis FJ, Frishman D, Shneider A. Specific temperature-induced perturbations of secondary mRNA structures are associated with the cold-adapted temperature-sensitive phenotype of influenza A virus. RNA Biol 2012; 9:1266-74. [PMID: 22995831 PMCID: PMC3583857 DOI: 10.4161/rna.22081] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
For decades, cold-adapted, temperature-sensitive (ca/ts) strains of influenza A virus have been used as live attenuated vaccines. Due to their great public health importance it is crucial to understand the molecular mechanism(s) of cold adaptation and temperature sensitivity that are currently unknown. For instance, secondary RNA structures play important roles in influenza biology. Thus, we hypothesized that a relatively minor change in temperature (32-39°C) can lead to perturbations in influenza RNA structures and, that these structural perturbations may be different for mRNAs of the wild type (wt) and ca/ts strains. To test this hypothesis, we developed a novel in silico method that enables assessing whether two related RNA molecules would undergo (dis)similar structural perturbations upon temperature change. The proposed method allows identifying those areas within an RNA chain where dissimilarities of RNA secondary structures at two different temperatures are particularly pronounced, without knowing particular RNA shapes at either temperature. We identified such areas in the NS2, PA, PB2 and NP mRNAs. However, these areas are not identical for the wt and ca/ts mutants. Differences in temperature-induced structural changes of wt and ca/ts mRNA structures may constitute a yet unappreciated molecular mechanism of the cold adaptation/temperature sensitivity phenomena.
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Affiliation(s)
- Andrey Chursov
- Department of Genome Oriented Bioinformatics, Technische Universität München, Wissenschaftzentrum Weihenstephan, Freising, Germany
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11
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Jaenson TGT, Hjertqvist M, Bergström T, Lundkvist A. Why is tick-borne encephalitis increasing? A review of the key factors causing the increasing incidence of human TBE in Sweden. Parasit Vectors 2012; 5:184. [PMID: 22937961 PMCID: PMC3439267 DOI: 10.1186/1756-3305-5-184] [Citation(s) in RCA: 134] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2012] [Accepted: 08/17/2012] [Indexed: 12/30/2022] Open
Abstract
The highest annual incidence of human tick-borne encephalitis (TBE) in Sweden ever recorded by the Swedish Institute for Communicable Disease Control (SMI) occurred last year, 2011. The number of TBE cases recorded during 2012 up to 6th August 2012 indicates that the incidence for 2012 could exceed that of 2011. In this review of the ecology and epidemiology of TBE in Sweden our main aim is to analyse the possible reasons behind the gradually increasing incidence of human TBE during the last 20 years. The main TBE virus (TBEV) vector to humans in Sweden is the nymphal stage of the common tick Ixodes ricinus. The main mode of transmission and maintenance of TBEV in the tick population is considered to be when infective nymphs co-feed with uninfected but infectible larvae on rodents. In most locations the roe deer, Capreolus capreolus is the main host for the reproducing adult I. ricinus ticks. The high number of roe deer for more than three decades has resulted in a very large tick population. Deer numbers have, however, gradually declined from the early 1990s to the present. This decline in roe deer numbers most likely made the populations of small rodents, which are reservoir-competent for TBEV, gradually more important as hosts for the immature ticks. Consequently, the abundance of TBEV-infected ticks has increased. Two harsh winters in 2009-2011 caused a more abrupt decline in roe deer numbers. This likely forced a substantial proportion of the "host-seeking" ticks to feed on bank voles (Myodes glareolus), which at that time suddenly had become very numerous, rather than on roe deer. Thus, the bank vole population peak in 2010 most likely caused many tick larvae to feed on reservoir-competent rodents. This presumably resulted in increased transmission of TBEV among ticks and therefore increased the density of infected ticks the following year. The unusually warm, humid weather and the prolonged vegetation period in 2011 permitted nymphs and adult ticks to quest for hosts nearly all days of that year. These weather conditions stimulated many people to spend time outdoors in areas where they were at risk of being attacked by infective nymphs. This resulted in at least 284 human cases of overt TBE. The tick season of 2012 also started early with an exceptionally warm March. The abundance of TBEV-infective "hungry" ticks was presumably still relatively high. Precipitation during June and July was rich and will lead to a "good mushroom season". These factors together are likely to result in a TBE incidence of 2012 similar to or higher than that of 2011.
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Affiliation(s)
- Thomas G T Jaenson
- Medical Entomology Unit, Department of Systematic Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18d, Uppsala SE-752 36, Sweden.
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12
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Bertrand Y, Töpel M, Elväng A, Melik W, Johansson M. First dating of a recombination event in mammalian tick-borne flaviviruses. PLoS One 2012; 7:e31981. [PMID: 22384119 PMCID: PMC3285191 DOI: 10.1371/journal.pone.0031981] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2011] [Accepted: 01/19/2012] [Indexed: 11/18/2022] Open
Abstract
The mammalian tick-borne flavivirus group (MTBFG) contains viruses associated with important human and animal diseases such as encephalitis and hemorrhagic fever. In contrast to mosquito-borne flaviviruses where recombination events are frequent, the evolutionary dynamic within the MTBFG was believed to be essentially clonal. This assumption was challenged with the recent report of several homologous recombinations within the Tick-borne encephalitis virus (TBEV). We performed a thorough analysis of publicly available genomes in this group and found no compelling evidence for the previously identified recombinations. However, our results show for the first time that demonstrable recombination (i.e., with large statistical support and strong phylogenetic evidences) has occurred in the MTBFG, more specifically within the Louping ill virus lineage. Putative parents, recombinant strains and breakpoints were further tested for statistical significance using phylogenetic methods. We investigated the time of divergence between the recombinant and parental strains in a Bayesian framework. The recombination was estimated to have occurred during a window of 282 to 76 years before the present. By unravelling the temporal setting of the event, we adduce hypotheses about the ecological conditions that could account for the observed recombination.
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Affiliation(s)
- Yann Bertrand
- Department of Plant and Environmental Sciences, Göteborg University, Göteborg, Sweden.
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