Highly Pathogenic Avian Influenza H5N8 in Poland in 2019-2020

Abstract

Introduction: Repeated incursions of highly pathogenic avian influenza virus (HPAIV) H5 subtype of Gs/GD lineage pose a serious threat to poultry worldwide. We provide a detailed analysis of the spatio-temporal spread and genetic characteristics of HPAIV Gs/GD H5N8 from the 2019/20 epidemic in Poland.

Material and methods: Samples from poultry and free-living birds were tested by real-time RT-PCR. Whole genome sequences from 24 (out of 35) outbreaks were generated and genetic relatedness was established. The clinical status of birds and possible pathways of spread were analysed based on the information provided by veterinary inspections combined with the results of phylogenetic studies.

Results: Between 31 December 2019 and 31 March 2020, 35 outbreaks in commercial and backyard poultry holdings and 1 case in a wild bird were confirmed in nine provinces of Poland. Most of the outbreaks were detected in meat turkeys and ducks. All characterised viruses were closely related and belonged to a previously unrecognised genotype of HPAIV H5N8 clade 2.3.4.4b. Wild birds and human activity were identified as the major modes of HPAIV spread.

Conclusion: The unprecedentedly late introduction of the HPAI virus urges for re-evaluation of current risk assessments. Continuous vigilance, strengthening biosecurity and intensifying surveillance in wild birds are needed to better manage the risk of HPAI occurrence in the future.

Keywords: H5N8; epidemic; highly pathogenic avian influenza.

Fig. 1

Location of HPAI H5N8 outbreaks in Poland between 31 December 2019 and 31 March, 2020 (white dots: commercial farms; purple dots: backyard holdings; asterisk: wild bird)

Fig. 2

Maximum clade credibility phylogenetic tree of the HA gene segment of H5N8 viruses sequenced in the present study and sequences available in the EpiFlu GISAID database. The European H5N8 viruses from the 2018/2020 epidemic are highlighted with blue and green. The names of Polish strains are coloured red and are labelled according to the legend. The posterior probability values are indicated next to the nodes