Novel reassortant clade 2.3.4.4 avian influenza A(H5N5) virus in wild birds and poultry, Croatia, 2016-2017

Abstract

Highly pathogenic avian influenza (HPAI) causes flock mortality as high as 100% in susceptible poultry species but it also poses a threat for humans, particularly viruses of A/goose/Guangdong/96-like (GD/96) lineage. The emergence of novel HPAI viruses in migratory birds is of concern because of the potential for virus spread during migration. In late 2016, novel GD/96 reassortant clade 2.3.4.4 group B avian influenza H5N5 virus was detected in wild birds and domestic poultry in Croatia, concurrently with numerous detections of H5N8 virus of the same clade and group. Sequencing of the full genome of the H5N8 index case isolate (October 2016) and of all three H5N5 isolates (December 2016 -March 2017) has shown that the novel H5N5 reassortant virus most likely emerged as a result of complex reassortment process in Asia from HPAI H5N8 viruses after the later viruses have became established in wild bird population. Concurrent findings of both, H5N5 and H5N8 viruses, at the same locations in Croatia indicate that the H5N5 reassortant virus was introduced from Asia as a subpopulation of H5N8 viruses by the same wild bird flyways. Although the novel H5N5 reassortant virus possesses haemagglutinin of the GD/96 lineage, the virus genome has typical avian virus traits. Apart from mutations T215A in M1 protein and P42S in NS1 protein which are associated to increased virulence in mice, none of the mutations related to increased affinity to human-type (α-2,6) receptors and mammalian host adaptation were found. Nevertheless, the virus poses a serious threat to the poultry industry since high pathogenicity for gallinaceous birds was confirmed by high intravenous pathogenicity index (2.87).

Spread of Highly Pathogenic Avian Influenza (HPAI) H5N5 Viruses in Europe in 2016–2017 Appears Related to the Timing of Reassortment Events

“…However, no changes in replication kinetics between the viruses were observed. The high in vitro cytopathogenicity and fast kinetics of virus replication are in accordance with the high IVPI scores that were reported for H5N5 viruses of genotypes H5N5-GT1 (3.00) ([21], unpublished results) and H5N5-GT2 (2.87–3.00) [22,24], which were comparable to H5N8 viruses (2.85–3.00) [13,22,23]. The H5N5 and H5N8 viruses carry the same HA, MP and NS gene segments, suggesting that the viral genetic factors associated with the high pathogenicity are likely present in these genes.…”

“…As previously reported, this genotype clustered phylogenetically with H5N8 viruses found in the Netherlands [21]. Therefore, H5N5-GT1 virus likely derived from reassortment of HPAI H5N8 and co-circulating LPAI viruses in the PA and NA genes [21,23,24]. As no viruses with the same gene constellation were detected and recent sequence data on genetically related LPAI viruses was missing, molecular clock analysis could not be used to estimate the timing of the reassortment event giving rise to this genotype.…”

“…During the HPAI H5N8 clade 2.3.4.4 group B epizootic in 2016–2017, multiple reassortant variants of subtype H5N5 were detected in Europe [19,20,21,22,23,24,25,26]. However, the number of birds detected with HPAI H5N5 virus was limited compared to H5N8 [19].…”

“…After the first detection of HPAI H5N5 virus in the Kamchatka region of Russia in October 2016 [20], a total of 24 outbreaks were reported in 11 European countries [19,20,21,22,23,24,25,26], mainly affecting wild birds. Infections of poultry and captive birds were reported during eight outbreaks [23,24,25]. Genetic analysis suggested that different H5N5 variants were introduced into Europe [21,23,26].…”

“…Genetic analysis suggested that different H5N5 variants were introduced into Europe [21,23,26]. These H5N5 viruses contained the same HA cleavage site (PLREKRRKR/GLF) as was observed in the majority of the H5N8 isolates [20,21,22,24], and showed intravenous pathogenicity index (IVPI) scores in chickens comparable to H5N8 [22,24]. However, the limited number of infected birds may suggest that the H5N5 viruses exhibit characteristics different from H5N8, such as decreased infectivity, transmissibility or pathogenicity.…”