Rapid virulence shift of an H5N2 avian influenza virus during a single passage in mice
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Influenza A viruses must undergo adaptation to acquire virulence in new host species. In mouse models, host adaptation for virulence is generally performed through 5 to 20 lung-to-lung passages. However, highly pathogenic avian influenza viruses (e.g., H5N1 and H7N7 subtypes) have been observed to acquire virulence in mice after only a few in vivo passages. In this study, a low-pathogenic avian influenza H5N2 virus, A/Aquatic Bird/Korea/CN2/2009, which was a prevalent subtype in South Korea in 2009, was serially passaged in mice to evaluate its potential to become highly pathogenic. Unexpectedly, the virus became highly pathogenic in mice after a single lung-to-lung passage, resulting in 100% lethality with a mean death time (MDT) of 6.1 days postinfection (DPI). Moreover, the pathogenicity gradually increased after subsequent in vivo passages with an MDT of 5.2 and 4.2 DPI after the second and third passage, respectively. Our molecular analysis revealed that two amino acid changes in the polymerase complex (a glutamate-to-lysine substitution at position 627 of PB2 and a threonine-to-isoleucine substitution at position 97 of PA) were associated with the increased pathogenicity; the PB2 E627K mutation was responsible for the initial virulence conversion (0 to 100% lethality), while the PA T97I mutation acted as an accessory for the increased virulence.
This work was supported by Grants from the Korea Institute for Planning and Evaluation of Technology in Food, Agriculture, Forestry and Fisheries (IPET) through the Animal Disease Management Technology Development Program, funded by Ministry of Agriculture, Food and Rural Affairs (MAFRA) (Grant no. 316042-03-2-HD020) and the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health and Welfare, Republic of Korea (Grant no. HD16A1487).
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Conflict of interest
All authors confirm that they have no conflict of interest.
All animal experiments were performed in biosafety level 2 plus (BSL2+) facilities at Korea Research Institute of Bioscience and Biotechnology (KRIBB) (Daejeon, South Korea) and were approved by the Institutional Animal Use and Care Committee of the KRIBB in accordance with the recommendations in the National Institutes of Health Guide for the Care and Use of Laboratory Animals (KRIBB-AEC-15191).
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