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Imprint
Elucidation of virulence determinants of highly pathogenic non-H5, non-H7 avian influenza viruses
Project
Project code: FLI-IMVZ-08-Ri-0456, 279378352
Contract period: 01.07.2016
- 30.06.2019
Purpose of research: Applied research
The 16 hemagglutinin (HA) subtypes of avian influenza viruses (AIV) in birds are classified into low pathogenic (LP) or highly pathogenic (HP). Up to now, HP avian influenza (fowl plague) was only caused by viruses specifying subtypes H5 and H7 with a multiple basic cleavage site (CS) within the HA protein. Interestingly, there are four non-H5/H7 strains complying with the official definition of HPAIV; one H4N2 virus originated from quails in the USA and three H10 viruses isolated from birds in Europe. Virulence markers of those viruses are not known to date but can be investigated using reverse genetics systems for AIV that have been established in our laboratory. The H4N2 virus possesses a multiple basic CS at the HA but displayed low virulence in chickens and did not grow in cell culture without the addition of exogenous trypsin. The potential of H4N2 to shift to an HP phenotype will be investigated (1) after serial passages in embryonated chicken eggs or chickens, (2) by increasing the number of multiple basic amino acids at the HA CS, and (3) by reassortment with HPAI H5/H7 viruses. Conversely, H10 viruses possess a monobasic CS but exhibit variable pathogenicity in chickens after intranasal or intravenous infection. Host immune response, difference in the cleavability of the HA by proteases in the respiratory tract or the temperature of the latter vs. body temperature of birds may modulate disease outcome and will be investigated. Moreover, two H7N7 and H7N9 viruses which produced lethal infections in humans in 2003 in the Netherlands and in 2013-2014 in China, respectively, acquired their neuraminidase segments from H10 viruses. The genetic compatibility to reassort with human viruses and the ability to replicate to high titers in infected mammals, indicate a significant pandemic potential of H10 viruses. Therefore, knowledge with regard to virulence, pathogenesis, adaptation and treatment merit further investigations. Additionally, H10 and H7 subtypes (which are commonly isolated from birds in Europe) are genetically closely related. Thus, reassortment with H7 HPAIV needs to be experimentally analysed. In summary, the low virulent, recent H4N2 virus is the first naturally occurring non-H5/H7 avian virus with multibasic CS within the HA. In contrast, some H10 viruses with monobasic CS motifs are of high virulence in poultry and exhibit pandemic potential. Therefore, investigations on molecular genetics of these viruses will unravel interesting facets on the virulence of AIV which mitigate the potential health hazards for both animals and humans.
Adaptive mutations in seal H10N7 virus: (Dittrich et al. 2017). In the first period of this project, The impact of 8 unique mutations in the HA1 protein of seal H10N7 was studied in vitro. Results showed that the seal H10N7 virus exhibited dual receptor binding affinity to avian and mammal-type sialic acid receptors. Affinity to mammal-type receptors was conferred by Q220L in the rim of the receptor binding pocket which increased the affinity of an avian H10N4 virus to mammal-type receptors and completely abolished the affinity to avian-type receptors. Firstly, these results indicate that H10N7 acquired adaptive mutations in the HA1 subunit to enhance replication in mammalian cells and retained replication efficiency in the original avian host. Secondly, mutations in the same position were essential for the adaptation of avian H2N2 and H3N2 subtypes in humans and equine H3N8 virus in dogs, which emphasize the potential zoonotic role of seals as a mixing vessel or adaptation of AIV from birds to other mammals. Evolution of non-H5/H7 highly pathogenic (HP) avian influenza virus (AIV) (Gischke et al. 2020). In the first period of this project, using reverse genetic and animal experiments we studied the evolution of HPAIV from a unique H4N2 with a natural polybasic HA cleavage site (CS) resembling the classic HPAIV H5/H7 viruses. Removal of highly conserved glycosylation site adjacent to the HACS increased virus spread in different organs in chicken embryos, however, it did not affect the low virulence of H4N2 in chickens. Increased number of basic amino acids in the HACS negatively affected virus transmission and excretion in chickens. These results may explain why non-H5/H7 with polybasic HACS are not common in nature. Reassortment with HPAIV H5N1, but not HPAIV H7N7, increased virulence of H4N2 virus. This indicates that evolution of HPAIV H4N2 requires specific constellation of gene segments similar to those of H5N1, which may also explain why HPAIV H4N2 were not isolated until now. Dittrich A, Scheibner D, Salaheldin AH, Veits J, Gischke M, Mettenleiter TC, Abdelwhab EM. Impact of Mutations in the Hemagglutinin of H10N7 Viruses Isolated from Seals on Virus Replication in Avian and Human Cells. Viruses 2018; 10. doi pii: E83. doi: 10.3390/v10020083. Gischke M, Ulrich R, Fatola O I, Scheibner D, Salaheldin A H, Crossley B, Böttcher-Friebertshäuser E, Veits J, Mettenleiter TC, Abdelwhab EM. Insertion of basic amino acids in the hemagglutinin cleavage site of H4N2 avian influenza virus (AIV) reduced virus fitness in chickens which is restored by reassortment with highly pathogenic H5N1 AIV. International Journal of Molecular Science 2020. doi: 10.20944/preprints202002.0391.v1
Section overview
Subjects
- Animal health
- Special animal species
Framework programme
Funding programme
Excutive institution
FLI - Institute of Molecular Virology and Cell Biology (FLI - IMVZ)
