Highly pathogenic avian influenza H5Nx in Poland in 2020/2021: a descriptive epidemiological study of a large-scale epidemic

Abstract

Introduction Highly pathogenic avian influenza (HPAI) outbreaks caused by the Gs/Gd lineage of H5Nx viruses occur in Poland with increased frequency. The article provides an update on the HPAI situation in the 2020/2021 season and studies the possible factors that caused the exceptionally fast spread of the virus. Material and Methods Samples from poultry and wild birds delivered for HPAI diagnosis were tested by real-time RT-PCR and a representative number of detected viruses were submitted for partial or full-genome characterisation. Information yielded by veterinary inspection was used for descriptive analysis of the epidemiological situation. Results The scale of the epidemic in the 2020/2021 season was unprecedented in terms of duration (November 2020–August 2021), number of outbreaks in poultry (n = 357), wild bird events (n = 92) and total number of affected domestic birds (approximately ~14 million). The major drivers of the virus spread were the harsh winter conditions in February 2020 followed by the introduction of the virus to high-density poultry areas in March 2021. All tested viruses belonged to H5 clade 2.3.4.4b with significant intra-clade diversity and in some cases clearly distinguished clusters. Conclusion The HPAI epidemic in 2020/2021 in Poland struck with unprecedented force. The conventional control measures may have limited effectiveness to break the transmission chain in areas with high concentrations of poultry.

Avian influenza overview March – June 2022

“…Information extracted from the scientific literature There were two studies on the phenotype of HPAI viruses in poultry in Europe. Smietanka et al (2022) described the epidemiology of the HPAI H5N8 virus, clade 2.3.4.4b, infection in Poland in 2021/2022 in poultry of different species and purposes: chicken layers (both breeders and hens laying eggs for consumption), meat turkeys, fattening ducks, breeder geese, fattening geese, broiler chickens and breeder ducks. The disease usually began with the drop in feed and/or water consumption that was accompanied (or quickly followed) by increased mortality and a drop in egg production (the latter not always observed in hens at the onset of clinical problems), depression, on some occasions shortness of breath, other respiratory signs (conjunctivitis, nasal discharge, sneezing) and diarrhoea.…”

Highly Pathogenic Avian Influenza (HPAI H5Nx, Clade 2.3.4.4.b) in Poultry and Wild Birds in Sweden: Synopsis of the 2020–2021 Season

“…The sequenced viruses detected in poultry and captive birds clustered phylogenetically with the sequences detected in wild birds ( Figure 4 ). Reports of HPAI outbreaks in other European countries also describe wild birds as the main source of introduction of HPAI to poultry [ 33 , 34 ]. Except for non-commercial flocks, all poultry were confined indoors during the 2020–2021 season as there was a nationwide housing order enforced in Sweden.…”

“…Several countries in Europe confirmed secondary spread of HPAI between poultry farms during the 2020–2021 season [ 29 , 34 ]. From the epidemiological investigations and the phylogenetic analysis, secondary spread between farms through direct or indirect contact was not confirmed in Sweden.…”

“…Also, the poultry population in Sweden consists mainly of chickens and the population of ducks and geese is very small. Many cases of secondary spread reported from other European countries have involved anseriform birds [ 29 , 34 , 39 , 40 ]. Another factor that may mitigate the risk of spread between farms is the long history of prevention of Salmonella spp., Campylobacter spp.…”

“…This may be the result of a variety of factors such as genetics [ 48 ], husbandry routines, and biosecurity levels. In other countries, duck and/or geese production has been severely affected by HPAI [ 34 , 39 ]. In Sweden, no cases of HPAI were confirmed in commercial anseriform poultry, but as discussed above, this production is very limited.…”