Research Open Access
Like 0



Over a 3-week period in late June/early July 2023, Poland experienced an outbreak caused by highly pathogenic avian influenza (HPAI) A(H5N1) virus in cats.


This study aimed to characterise the identified virus and investigate possible sources of infection.


We performed next generation sequencing and phylogenetic analysis of detected viruses in cats.


We sampled 46 cats, and 25 tested positive for avian influenza virus. The identified viruses belong to clade, genotype CH (H5N1 A/Eurasian wigeon/Netherlands/3/2022-like). In Poland, this genotype was responsible for several poultry outbreaks between December 2022 and January 2023 and has been identified only sporadically since February 2023. Viruses from cats were very similar to each other, indicating one common source of infection. In addition, the most closely related virus was detected in a dead white stork in early June. Influenza A(H5N1) viruses from cats possessed two amino acid substitutions in the PB2 protein (526R and 627K) which are two molecular markers of virus adaptation in mammals. The virus detected in the white stork presented one of those mutations (627K), which suggests that the virus that had spilled over to cats was already partially adapted to mammalian species.


The scale of HPAI H5N1 virus infection in cats in Poland is worrying. One of the possible sources seems to be poultry meat, but to date no such meat has been identified with certainty. Surveillance should be stepped up on poultry, but also on certain species of farmed mammals kept close to infected poultry farms.


Article metrics loading...

Loading full text...

Full text loading...



  1. Adlhoch C, Fusaro A, Gonzales JL, Kuiken T, Mirinaviciute G, Niqueux É, et al. Avian influenza overview March - April 2023. EFSA J. 2023;21(6):e08039. PMID: 37293570 
  2. Adlhoch C, Baldinelli F, Fusaro A, Terregino C. Avian influenza, a new threat to public health in Europe? Clin Microbiol Infect. 2022;28(2):149-51.  https://doi.org/10.1016/j.cmi.2021.11.005  PMID: 34763057 
  3. Adlhoch C, Fusaro A, Gonzales JL, Kuiken T, Marangon S, Niqueux É, et al. Avian influenza overview June - September 2022. EFSA J. 2022;20(10):e07597. PMID: 36247870 
  4. European Commission. Commission Delegated Regulation (EU) 2020/689 of 17 December 2019 supplementing Regulation (EU) 2016/429 of the European Parliament and of the Council as regards rules for surveillance, eradication programmes, and disease-free status for certain listed and emerging diseases. Official Journal of the European Union. Luxembourg: Publications Office of the European Union. 3.6.2020:L174/211. Available from: http://data.europa.eu/eli/reg_del/2020/689/oj
  5. Government of the Republic of Poland. Rozporządzenie Ministra Rolnictwa i Rozwoju Wsi z dnia 23 marca 2023 r. w sprawie wprowadzenia „Krajowego programu mającego na celu wykrycie zakażeń wirusami wywołującymi grypę ptaków (Avian influenza) u drobiu i dzikich ptaków na 2023 r. [Regulation of the Minister of Agriculture and Rural Development of 23 March 2023 on the introduction of the "National program aimed at detecting infections with viruses causing avian influenza (Avian influenza) in poultry and wild birds for 2023]. Dz.U z dnia 31 marca 2023, poz. 618. 2023. Polish. Available from: https://isap.sejm.gov.pl/isap.nsf/download.xsp/WDU20230000618/O/D20230618.pdf
  6. Spackman E, Senne DA, Myers TJ, Bulaga LL, Garber LP, Perdue ML, et al. Development of a real-time reverse transcriptase PCR assay for type A influenza virus and the avian H5 and H7 hemagglutinin subtypes. J Clin Microbiol. 2002;40(9):3256-60.  https://doi.org/10.1128/JCM.40.9.3256-3260.2002  PMID: 12202562 
  7. Slomka MJ, Pavlidis T, Banks J, Shell W, McNally A, Essen S, et al. Validated H5 Eurasian real-time reverse transcriptase-polymerase chain reaction and its application in H5N1 outbreaks in 2005-2006. Avian Dis. 2007;51(1) Suppl;373-7.  https://doi.org/10.1637/7664-060906R1.1  PMID: 17494587 
  8. Hoffmann B, Hoffmann D, Henritzi D, Beer M, Harder TC. Riems influenza a typing array (RITA): An RT-qPCR-based low density array for subtyping avian and mammalian influenza a viruses. Sci Rep. 2016;6(1):27211.  https://doi.org/10.1038/srep27211  PMID: 27256976 
  9. Śmietanka K, Świętoń E, Kozak E, Wyrostek K, Tarasiuk K, Tomczyk G, et al. Highly pathogenic avian influenza H5N8 in Poland in 2019-2020. J Vet Res (Pulawy). 2020;64(4):469-76.  https://doi.org/10.2478/jvetres-2020-0078  PMID: 33367134 
  10. Nguyen LT, Schmidt HA, von Haeseler A, Minh BQ. IQ-TREE: a fast and effective stochastic algorithm for estimating maximum-likelihood phylogenies. Mol Biol Evol. 2015;32(1):268-74.  https://doi.org/10.1093/molbev/msu300  PMID: 25371430 
  11. Hoang DT, Chernomor O, von Haeseler A, Minh BQ, Vinh LS. UFBoot2: Improving the Ultrafast Bootstrap Approximation. Mol Biol Evol. 2018;35(2):518-22.  https://doi.org/10.1093/molbev/msx281  PMID: 29077904 
  12. Bandelt HJ, Forster P, Röhl A. Median-joining networks for inferring intraspecific phylogenies. Mol Biol Evol. 1999;16(1):37-48.  https://doi.org/10.1093/oxfordjournals.molbev.a026036  PMID: 10331250 
  13. Suttie A, Deng Y-M, Greenhill AR, Dussart P, Horwood PF, Karlsson EA. Inventory of molecular markers affecting biological characteristics of avian influenza A viruses. Virus Genes. 2019;55(6):739-68.  https://doi.org/10.1007/s11262-019-01700-z  PMID: 31428925 
  14. Subbarao EK, London W, Murphy BR. A single amino acid in the PB2 gene of influenza A virus is a determinant of host range. J Virol. 1993;67(4):1761-4.  https://doi.org/10.1128/jvi.67.4.1761-1764.1993  PMID: 8445709 
  15. Hatta M, Gao P, Halfmann P, Kawaoka Y. Molecular basis for high virulence of Hong Kong H5N1 influenza A viruses. Science. 2001;293(5536):1840-2.  https://doi.org/10.1126/science.1062882  PMID: 11546875 
  16. Salomon R, Franks J, Govorkova EA, Ilyushina NA, Yen H-L, Hulse-Post DJ, et al. The polymerase complex genes contribute to the high virulence of the human H5N1 influenza virus isolate A/Vietnam/1203/04. J Exp Med. 2006;203(3):689-97.  https://doi.org/10.1084/jem.20051938  PMID: 16533883 
  17. Shinya K, Hamm S, Hatta M, Ito H, Ito T, Kawaoka Y. PB2 amino acid at position 627 affects replicative efficiency, but not cell tropism, of Hong Kong H5N1 influenza A viruses in mice. Virology. 2004;320(2):258-66.  https://doi.org/10.1016/j.virol.2003.11.030  PMID: 15016548 
  18. Steel J, Lowen AC, Mubareka S, Palese P. Transmission of influenza virus in a mammalian host is increased by PB2 amino acids 627K or 627E/701N. PLoS Pathog. 2009;5(1):e1000252.  https://doi.org/10.1371/journal.ppat.1000252  PMID: 19119420 
  19. Mehle A, Doudna JA. An inhibitory activity in human cells restricts the function of an avian-like influenza virus polymerase. Cell Host Microbe. 2008;4(2):111-22.  https://doi.org/10.1016/j.chom.2008.06.007  PMID: 18692771 
  20. Hatta M, Hatta Y, Kim JH, Watanabe S, Shinya K, Nguyen T, et al. Growth of H5N1 influenza A viruses in the upper respiratory tracts of mice. PLoS Pathog. 2007;3(10):1374-9.  https://doi.org/10.1371/journal.ppat.0030133  PMID: 17922570 
  21. Labadie K, Dos Santos Afonso E, Rameix-Welti MA, van der Werf S, Naffakh N. Host-range determinants on the PB2 protein of influenza A viruses control the interaction between the viral polymerase and nucleoprotein in human cells. Virology. 2007;362(2):271-82.  https://doi.org/10.1016/j.virol.2006.12.027  PMID: 17270230 
  22. Rameix-Welti MA, Tomoiu A, Dos Santos Afonso E, van der Werf S, Naffakh N. Avian Influenza A virus polymerase association with nucleoprotein, but not polymerase assembly, is impaired in human cells during the course of infection. J Virol. 2009;83(3):1320-31.  https://doi.org/10.1128/JVI.00977-08  PMID: 19019950 
  23. Fornek JL, Gillim-Ross L, Santos C, Carter V, Ward JM, Cheng LI, et al. A single-amino-acid substitution in a polymerase protein of an H5N1 influenza virus is associated with systemic infection and impaired T-cell activation in mice. J Virol. 2009;83(21):11102-15.  https://doi.org/10.1128/JVI.00994-09  PMID: 19692471 
  24. Knief U, Bregnballe T, Alfarwi I, Ballmann M, Brenninkmeijer A, Bzoma S, et al. Highly pathogenic avian influenza causes mass mortality in Sandwich tern (Thalasseus sandvicensis) breeding colonies across northwestern Europe. bioRxiv. 2023:2023.05.12.540367. Preprint.
  25. Gobbo F, Zanardello C, Bottinelli M, Budai J, Bruno F, De Nardi R, et al. Silent infection of highly pathogenic avian influenza virus (H5N1) clade in a commercial chicken broiler flock in Italy. Viruses. 2022;14(8):1600.  https://doi.org/10.3390/v14081600  PMID: 35893671 
  26. Kandeil A, Patton C, Jones JC, Jeevan T, Harrington WN, Trifkovic S, et al. Rapid evolution of A(H5N1) influenza viruses after intercontinental spread to North America. Nat Commun. 2023;14(1):3082.  https://doi.org/10.1038/s41467-023-38415-7  PMID: 37248261 
  27. Li J, Ishaq M, Prudence M, Xi X, Hu T, Liu Q, et al. Single mutation at the amino acid position 627 of PB2 that leads to increased virulence of an H5N1 avian influenza virus during adaptation in mice can be compensated by multiple mutations at other sites of PB2. Virus Res. 2009;144(1-2):123-9.  https://doi.org/10.1016/j.virusres.2009.04.008  PMID: 19393699 
  28. Song W, Wang P, Mok BW, Lau SY, Huang X, Wu WL, et al. The K526R substitution in viral protein PB2 enhances the effects of E627K on influenza virus replication. Nat Commun. 2014;5(1):5509.  https://doi.org/10.1038/ncomms6509  PMID: 25409547 
  29. Kosicki J, Profus P, Dolata P, Tobółka M. Food composition and energy demand of the white stork Ciconia ciconia breeding population. Literature survey and preliminary results from Poland. In: Tryjanowski P, Sparks T, Jerzak L (eds). The white stork in Poland: studies in biology, ecology and conservation. Poznań: Bogucki Wyd. Nauk; 2006. p. 169-83. Available from: https://www.researchgate.net/publication/237325391_Food_composition_and_energy_demand_of_the_White_Stork_Ciconia_ciconia_breeding_population_Literature_survey_and_preliminary_results_from_Poland
  30. Velkers FC, Blokhuis SJ, Veldhuis Kroeze EJB, Burt SA. The role of rodents in avian influenza outbreaks in poultry farms: a review. Vet Q. 2017;37(1):182-94.  https://doi.org/10.1080/01652176.2017.1325537  PMID: 28460593 
  31. Romero Tejeda A, Aiello R, Salomoni A, Berton V, Vascellari M, Cattoli G. Susceptibility to and transmission of H5N1 and H7N1 highly pathogenic avian influenza viruses in bank voles (Myodes glareolus). Vet Res. 2015;46(1):51.  https://doi.org/10.1186/s13567-015-0184-1  PMID: 25963535 
  32. Shriner SA, VanDalen KK, Mooers NL, Ellis JW, Sullivan HJ, Root JJ, et al. Low-pathogenic avian influenza viruses in wild house mice. PLoS One. 2012;7(6):e39206.  https://doi.org/10.1371/journal.pone.0039206  PMID: 22720076 
  33. World Health Organization (WHO). Ongoing avian influenza outbreaks in animals pose risk to humans. Situation analysis and advice to countries from FAO, WHO, WOAH. Geneva/Paris/Rome: WHO/WOAH/FAO; 12 July 2023. Available from: www.who.int/news/item/12-07-2023-ongoing-avian-influenza-outbreaks-in-animals-pose-risk-to-humans
  34. European Food Safety Authority; European Centre for Disease Prevention and Control; European Reference Laboratory for Avian Influenza; Adlhoch C, Fusaro A, Gonzales JL, et al. Scientific report: Avian influenza overview April–June 2023. EFSA J. 2023;21(7):8191.  https://doi.org/10.2903/j.efsa.2023.8191 

Data & Media loading...

Supplementary data

Submit comment
Comment moderation successfully completed
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error