Epidemiologic and phylogenetic analyses suggest that the virus was repeatedly introduced and that the disease is maintained in wild boar.

Phylogenetic evidence from the recent resurgence of high-pathogenicity avian influenza (HPAI) virus subtype H5N1, clade 2.3.4.4b, observed in European wild birds and poultry since October 2021, suggests at least two different and distinct reservoirs. We propose contrasting hypotheses for this emergence: (i) resident viruses have been maintained, presumably in wild birds, in northern Europe throughout the summer of 2021 to cause some of the outbreaks that are part of the most recent autumn/winter 2021 epizootic, or (ii) further virus variants were reintroduced by migratory birds, and these two sources of reintroduction have driven the HPAI resurgence.

The spatial behaviour of hosts can seriously affect the transmission of pathogens and spatial spread of diseases. Understanding the relationship between host movements and disease dynamics is of prime importance for optimizing disease control efforts. African swine fever (ASF), a devastating disease of wild and domestic suids, has been spreading continuously through eastern Europe since 2007. The wild boar (Sus scrofa) has been implicated in the epidemiology of this disease, but the role of wild boar movements in ASF dynamics and spread has not been studied and remains largely speculative. Here, we examined whether monthly parameters of wild boar movements (dispersal distance of yearlings, home range size of adult males and females) can explain variation in the spatio-temporal dynamics of the ASF outbreak in the wild boar population in north-eastern Poland, 2014-2015. We expected to observe a positive relationship between host mobility and disease spread. Contrary to our expectations, we found that movements of wild boar, despite their seasonal variation, were poor predictors of ASF dynamics in space and time. During the 2 years of the study, ASF spread gradually at a steady pace of 1.5 km/month without significant changes across seasons. None of the analysed movement parameters explained variation in the measures of ASF occurrence and spread (i.e., number of cases, prevalence, size and expansion rate of the outbreak area). We believe that the factor limiting the influence of host movements on ASF dynamics is the severity of the disease, which quickly hampers extensive movements and restricts disease transmission to only the most immediate individuals. Three natural factors constrain direct disease transmission: wild boar social structure, the short duration of low-level virus shedding and high virus-induced lethality, followed by indirect transmission through infected carcasses. These most likely shape the gradual spread of ASF in space and its persistence in already infected areas.

We analyzed the highly pathogenic avian influenza (HPAI) H5 epizootic of 2016–17 in Europe by epidemiologic and genetic characteristics and compared it with 2 previous epizootics caused by the same H5 Guangdong lineage. The 2016–17 epizootic was the largest in Europe by number of countries and farms affected and greatest diversity of wild birds infected. We observed significant differences among the 3 epizootics regarding region affected, epidemic curve, seasonality, and outbreak duration, making it difficult to predict future HPAI epizootics. However, we know that in 2005–06 and 2016–17 the initial peak of wild bird detections preceded the peak of poultry outbreaks within Europe. Phylogenetic analysis of 2016–17 viruses indicates 2 main pathways into Europe. Our findings highlight the need for global surveillance of viral changes to inform disease preparedness, detection, and control.

Article summary line: Phylogenetic and epidemiologic evidence shows incursion of HPAIV into the food chain.

Broiler chickens with clinical signs of uneven growth, depression, and dull feathers were submitted to our laboratory and, at necropsy, lesions in proventriculus, gizzard, and intestines were detected. Fowl adenovirus serotype 1 (FAdV-1) was isolated from digestive tissues. The virus, assigned as FAdV-PL/G068/08, showed 99.5% nucleotide homology and 99.2% amino acid homology in hexon gene with chicken embryo lethal orphan (CELO) strain classified as the European reference of FAdV-1. One-day-old and 21-d-old SPF chickens were inoculated with FAdV-PL/068/08 by both nasal and ocular routes and then observed daily and examined by necropsy at 6, 10, and 14 d postinoculation. Experimental infection with isolated virus was fatal for younger chickens and major lesions occurred in the gizzards. No clinical or pathological changes were observed in chickens infected at 21 d of age, but the presence of intranuclear inclusion bodies in gizzard epithelial cells was detected. Molecular characterization was based on the long and short fibers genes sequencing and comparison of obtained sequences with other FAdV-1 strains. The homology between FAdV-PL/G068/08 and other sequences available in GenBank was between 98.9 and 99.8% (short fiber region) and 99.0 and 99.7% (long fiber region) at nucleotide level and between 98.4 and 100% (short fiber region) and 99.3 and 99.9% (long fiber region) at amino acid level. No correlation between identified amino acid changes in short and long fiber proteins and pathogenicity of studied FAdV-1 strains was observed. Although short and long proteins were indicated as factors influencing virus pathogenicity, the role of identified sequence differences in infectivity determination remain unclear.

Persistence of H5N1 high pathogenicity avian influenza virus (HPAIV), isolated during the epidemic in wild birds in Poland in 2006, was evaluated in three water samples derived from the sources known to host wild water birds (city pond, Vistula river mouth, and Baltic Sea). The virus was tested at two concentrations (10(4) and 10(6) median tissue culture infective dose per milliliter) and at three temperatures (4 C, 10 C, and 20 C), representing average seasonal temperatures in Poland. All tested water samples were filtered before virus inoculation, and one unfiltered sample (Baltic seawater) was also tested. Infectivity was determined twice a week over a 60-day trial period by microtiter endpoint titration. The persistence of the virus varied considerably depending on its concentration and also on physico-chemical parameters of the water, such as temperature and salinity. Avian influenza virus survival was the highest at 4 C and the lowest at 20 C. Prolonged infectivity of the virus in Baltic seawater (brackish, 7.8 ppt) was also seen. In distilled water, the virus retained its infectivity beyond the 60-day study period. Interestingly, a devastating effect of the unfiltered fraction of seawater was seen as the virus disappeared in this fraction the quickest in all studied combinations; thus, biologic factors may also affect infectivity of HPAIV.

The A(H5N8) highly pathogenic avian influenza (HPAI) epidemic occurred in 29 European countries in 2016/2017 and has been the largest ever recorded in the EU in terms of number of poultry outbreaks, geographical extent and number of dead wild birds. Multiple primary incursions temporally related with all major poultry sectors affected but secondary spread was most commonly associated with domestic waterfowl species. A massive effort of all the affected EU Member States (MSs) allowed a descriptive epidemiological overview of the cases in poultry, captive birds and wild birds, providing also information on measures applied at the individual MS level. Data on poultry population structure are required to facilitate data and risk factor analysis, hence to strengthen science-based advice to risk managers. It is suggested to promote common understanding and application of definitions related to control activities and their reporting across MSs. Despite a large number of human exposures to infected poultry occurred during the ongoing outbreaks, no transmission to humans has been identified. Monitoring the avian influenza (AI) situation in other continents indicated a potential risk of long-distance spread of HPAI virus (HPAIV) A(H5N6) from Asia to wintering grounds towards Western Europe, similarly to what happened with HPAIV A(H5N8) and HPAIV A(H5N1) in previous years. Furthermore, the HPAI situation in Africa with A(H5N8) and A(H5N1) is rapidly evolving. Strengthening collaborations at National, EU and Global levels would allow close monitoring of the AI situation, ultimately helping to increase preparedness. No human case was reported in the EU due to AIVs subtypes A(H5N1), A(H5N6), A(H7N9) and A(H9N2). Direct transmission of these viruses to humans has only been reported in areas, mainly in Asia and Egypt, with a substantial involvement of wild bird and/or poultry populations. It is suggested to improve the collection and reporting of exposure events of people to AI. (7) of the above mentioned Decision, the concerned experts were allowed to take part in the discussions and in the drafting phase of the EFSA Scientific report on Avian influenza monitoring (Art. 31) -overview October 2016 -August 2017, and have not been allowed to be, or act as, a chairman, a vice-chairman or rapporteur of the WG.