Tick-borne encephalitis virus (TBEV) causes a severe and potentially fatal neuroinfection in humans. Despite its high medical relevance, no specific antiviral therapy is currently available. Here we demonstrate that treatment with a nucleoside analog, 7-deaza-2'-C-methyladenosine (7-deaza-2'-CMA), substantially improved disease outcomes, increased survival, and reduced signs of neuroinfection and viral titers in the brains of mice infected with a lethal dose of TBEV. To investigate the mechanism of action of 7-deaza-2'-CMA, two drug-resistant TBEV clones were generated and characterized. The two clones shared a signature amino acid substitution, S603T, in the viral NS5 RNA-dependent RNA polymerase (RdRp) domain. This mutation conferred resistance to various 2'-C-methylated nucleoside derivatives, but no cross-resistance was seen with other nucleoside analogs, such as 4'-C-azidocytidine and 2'-deoxy-2'-beta-hydroxy-4'-azidocytidine (RO-9187). All-atom molecular dynamics simulations revealed that the S603T RdRp mutant repels a water molecule that coordinates the position of a metal ion cofactor as 2'-C-methylated nucleoside analogs approach the active site. To investigate its phenotype, the S603T mutation was introduced into a recombinant TBEV strain (Oshima-IC) generated from an infectious cDNA clone and into a TBEV replicon that expresses a reporter luciferase gene (Oshima-REP-luc2A). The mutants were replication impaired, showing reduced growth and a small plaque size in mammalian cell culture and reduced levels of neuroinvasiveness and neurovirulence in rodent models. These results indicate that TBEV resistance to 2'-C-methylated nucleoside inhibitors is conferred by a single conservative mutation that causes a subtle atomic effect within the active site of the viral NS5 RdRp and is associated with strong attenuation of the virus.IMPORTANCE This study found that the nucleoside analog 7-deaza-2'-C-methyladenosine (7-deaza-2'-CMA) has high antiviral activity against tick-borne encephalitis virus (TBEV), a pathogen that causes severe human neuroinfections in large areas of Europe and Asia and for which there is currently no specific therapy. Treating mice infected with a lethal dose of TBEV with 7-deaza-2'-CMA resulted in significantly higher survival rates and reduced the severity of neurological signs of the disease. Thus, this compound shows promise for further development as an anti-TBEV drug. It is important to generate drug-resistant mutants to understand how the drug works and to develop guidelines for patient treatment. We generated TBEV mutants that were resistant not only to 7-deaza-2'-CMA but also to a broad range of other 2'-C-methylated antiviral medications. Our findings suggest that combination therapy may be used to improve treatment and reduce the emergence of drug-resistant viruses during nucleoside analog therapy for TBEV infection.

• Klíčová slova
• antiviral agents, antiviral therapy, escape mutant, tick-borne encephalitis virus, tick-borne pathogens,
• Publikační typ
• časopisecké články MeSH

Tick-borne encephalitis (TBE) is an acute febrile illness with neurological manifestations that is prevalent in forested areas of moderate climate in Europe and Asia. TBE virus is transmitted by ticks and rarely by unpasteurized milk and dairy products. The disease burden is attributed mainly to resulting long-term disability, especially in individuals over 50 y of age. Currently, there is no causative treatment, but a very effective vaccination is available with a good safety profile. The vaccination requires 3 basic doses to be fully effective and regular boosters afterwards. An accelerated vaccination schedule enables a patient to reach reasonably protective titres within 3 to 4 weeks from the first injection. The risk of travel-related TBE is estimated to be less than the risk of acquiring typhoid fever while visiting highly endemic regions in South Asia, but more than the risk of acquiring Japanese encephalitis, meningococcal invasive disease, or rabies. The pre-travel risk assessment of acquiring TBE should consider known risk factors which include 1) the country and regions to be visited; 2) April to November season; 3) altitude less than 1500 m above the sea level; 4) duration of stay; 5) the extent of tick-exposure associated activities including leisure and professional outdoor activities within the endemic area; and 6) age and comorbidities of the traveler. A major challenge, however, is the very low awareness of the risk of contracting TBE in those who travel to industrialized European countries.

• Klíčová slova
• endemic country, flavivirus, tick-borne encephalitis, tick-borne encephalitis virus, travel medicine, vaccination,
• MeSH
• cestování * MeSH
• endemické nemoci * MeSH
• klíšťová encefalitida epidemiologie   prevence a kontrola   MeSH
• lidé MeSH
• virové vakcíny aplikace a dávkování   imunologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Geografické názvy
• Asie epidemiologie   MeSH
• Evropa epidemiologie   MeSH
• Názvy látek
• virové vakcíny MeSH