Avian influenza overview February - May 2018

Experimental infection of chickens, Pekin ducks, Eurasian wigeons and Barnacle geese with two recent highly pathogenic avian influenza H5N1 clade 2.3.4.4b viruses

Multiple genotypes of highly pathogenic avian influenza (HPAI) H5 clade 2.3.4.4b viruses have caused epizootics in wild birds and poultry. The HPAI H5N1 genotype C virus caused a modest epizootic, whereas the occurrence of the HPAI H5N1 genotype AB virus in 2021 resulted in the largest avian influenza epizootic in Europe to date. Here we studied the pathogenicity of two HPAI H5N1 viruses by experimentally infecting chickens, Pekin ducks, Eurasian wigeons and Barnacle geese. Our study demonstrates that pathogenicity of the H5N1-2021-AB virus is lower in Pekin ducks, Eurasian wigeons and Barnacle geese compared to the H5N1-2020-C virus, whereas virus shedding was high for both viruses. After inoculation with H5N1-2021-C viral antigen expression was higher in the brain of Pekin ducks, Eurasian wigeons and Barnacle geese, which caused higher mortality compared to inoculation with H5N1-2021-AB virus. Subclinical infections occurred in Pekin ducks and Eurasian wigeons and mortality was reduced in Barnacle geese after inoculation with H5N1-2021-AB virus while H5N1-2020-C virus caused high morbidity and mortality in these species. This H5N1-2021-AB virus trait may have contributed to efficient spread of the virus in wild bird populations. Therefore, high mortality, virus shedding and long-lasting viral antigen expression found in Barnacle geese may have increased the risk for introduction into poultry.

In Ovo Models to Predict Virulence of Highly Pathogenic Avian Influenza H5-Viruses for Chickens and Ducks

Highly pathogenic avian influenza (HPAI) H5-viruses are circulating in wild birds and are repeatedly introduced to poultry causing outbreaks in the Netherlands since 2014. The largest epizootic ever recorded in Europe was caused by HPAI H5N1 clade 2.3.4.4b viruses in the period 2021-2022. The recent H5-clade 2.3.4.4 viruses were found to differ in their virulence for chickens and ducks. Viruses causing only mild disease may remain undetected, increasing the risk of virus spread to other farms, wild birds and mammals. We developed in ovo models to determine the virulence of HPAI viruses for chickens and ducks, which are fast and have low costs. The virulence of five contemporary H5-viruses was compared studying replication rate, average time to death and virus spread in the embryo. Remarkable differences in virulence were observed between H5-viruses and between poultry species. The H5N1-2021 virus was found to have a fast replication rate in both the chicken and duck in ovo models, but a slower systemic virus dissemination compared to three other H5-clade 2.3.4.4b viruses. The results show the potential of in ovo models to quickly determine the virulence of novel HPAI viruses, and study potential virulence factors which can help to better guide the surveillance in poultry.

Clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus (HPAIV) from the 2021/22 epizootic is highly duck adapted and poorly adapted to chickens

The 2021/2022 epizootic of high pathogenicity avian influenza (HPAIV) remains one of the largest ever in the UK, being caused by a clade 2.3.4.4b H5N1 HPAIV. This epizootic affected more than 145 poultry premises, most likely through independent incursion from infected wild birds, supported by more than 1700 individual detections of H5N1 from wild bird mortalities. Here an H5N1 HPAIV, representative of this epizootic (H5N1-21), was used to investigate its virulence, pathogenesis and transmission in layer chickens and Pekin ducks, two species of epidemiological importance. We inoculated both avian species with decreasing H5N1-21 doses. The virus was highly infectious in ducks, with high infection levels and accompanying shedding of viral RNA, even in ducks inoculated with the lowest dose, reflecting the strong waterfowl adaptation of the clade 2.3.4.4 HPAIVs. Duck-to-duck transmission was very efficient, coupled with high environmental contamination. H5N1-21 was frequently detected in water sources, serving as likely sources of infection for ducks, but inhalable dust and aerosols represented low transmission risks. In contrast, chickens inoculated with the highest dose exhibited lower rates of infection compared to ducks. There was no evidence for experimental H5N1-21 transmission to any naive chickens, in two stocking density scenarios, coupled with minimal and infrequent contamination being detected in the chicken environment. Systemic viral dissemination to multiple organs reflected the pathogenesis and high mortalities in both species. In summary, the H5N1-21 virus is highly infectious and transmissible in anseriformes, yet comparatively poorly adapted to galliformes, supporting strong host preferences for wild waterfowl. Key environmental matrices were also identified as being important in the epidemiological spread of this virus during the continuing epizootic.

Experimental and natural infections of white-tailed sea eagles (Haliaeetus albicilla) with high pathogenicity avian influenza virus of H5 subtype

White-tailed sea eagle (Haliaeetus albicilla), a regionally rare species of raptor, is threatened in several countries. To assess the risk of H5 high pathogenicity avian influenza (HPAI) viral infection in rare bird species, we performed experimental infections with a GS/GD96-lineage H5N6 HPAI virus of clade 2.3.4.4e in white-tailed sea eagles. Additionally, during the winter of 2020–2021 in Japan, we accidentally encountered a white-tailed sea eagle that had a fatal outcome due to natural infection with a GS/GD96-lineage H5N8 HPAI virus of clade 2.3.4.4b, allowing us to compare experimental and natural infections in the same rare raptor species. Our experiments demonstrated the susceptibility of white-tailed sea eagles to the GS/GD96-lineage H5 HPAI virus with efficient replication in systemic organs. The potential for the viruses to spread within the white-tailed sea eagle population through indirect transmission was also confirmed. Comprehensive comparisons of both viral distribution and histopathological observations between experimentally and naturally infected white-tailed sea eagles imply that viral replication in the brain is responsible for the disease severity and mortality in this species. These findings provide novel insights into the risk assessment of H5 HPAI viral infection in white-tailed sea eagles, proper diagnostic procedures, potential risks to artificially fed eagle populations and persons handling superficially healthy eagles, potential impact of intragastric infection on eagle outcomes, and possibility of severity of the disease being attributed to viral replication in the brain.

Evolutionary Dynamics of H5 Highly Pathogenic Avian Influenza Viruses (Clade 2.3.4.4B) Circulating in Bulgaria in 2019-2021

The first detection of a Highly Pathogenic Avian Influenza (HPAI) H5N8 virus in Bulgaria dates back to December 2016. Since then, many outbreaks caused by HPAI H5 viruses from clade 2.3.4.4B have been reported in both domestic and wild birds in different regions of the country. In this study, we characterized the complete genome of sixteen H5 viruses collected in Bulgaria between 2019 and 2021. Phylogenetic analyses revealed a persistent circulation of the H5N8 strain for four consecutive years (December 2016-June 2020) and the emergence in 2020 of a novel reassortant H5N2 subtype, likely in a duck farm. Estimation of the time to the most recent common ancestor indicates that this reassortment event may have occurred between May 2019 and January 2020. At the beginning of 2021, Bulgaria experienced a new virus introduction in the poultry sector, namely a HPAI H5N8 that had been circulating in Europe since October 2020. The periodical identification in domestic birds of H5 viruses related to the 2016 epidemic as well as a reassortant strain might indicate undetected circulation of the virus in resident wild birds or in the poultry sector. To avoid the concealed circulation and evolution of viruses, and the risk of emergence of strains with pandemic potential, the implementation of control measures is of utmost importance, particularly in duck farms where birds display no clinical signs.

Spatiotemporal reconstruction and transmission dynamics during the 2016-17 H5N8 highly pathogenic avian influenza epidemic in Italy

Effective control of avian diseases in domestic populations requires understanding of the transmission dynamics facilitating viral emergence and spread. In 2016-17, Italy experienced a significant avian influenza epidemic caused by a highly pathogenic A(H5N8) virus, which affected domestic premises housing around 2.7 million birds, primarily in the north-eastern regions with the highest density of poultry farms (Lombardy, Emilia-Romagna and Veneto). We perform integrated analyses of genetic, spatiotemporal and host data within a Bayesian phylogenetic framework. Using continuous and discrete phylogeography, we estimate the locations of movements responsible for the spread and persistence of the epidemic. The information derived from these analyses on rates of transmission between regions through time can be used to assess the success of control measures. Using an approach based on phylogenetic-temporal distances between domestic cases, we infer the presence of cryptic wild bird-mediated transmission, information that can be used to complement existing epidemiological methods for distinguishing transmission within the domestic population from incursions across the wildlife-domestic interface, a common challenge in veterinary epidemiology. Spatiotemporal reconstruction of the epidemic reveals a highly skewed distribution of virus movements with a high proportion of shorter distance local movements interspersed with occasional long-distance dispersal events associated with wild birds. We also show how such inference be used to identify possible instances of human-mediated movements where distances between phylogenetically linked domestic cases are unusually high.

Regional Transmission and Reassortment of 2.3.4.4b Highly Pathogenic Avian Influenza (HPAI) Viruses in Bulgarian Poultry 2017/18

Between 2017 and 2018, several farms across Bulgaria reported outbreaks of H5 highly-pathogenic avian influenza (HPAI) viruses. In this study we used genomic and traditional epidemiological analyses to trace the origin and subsequent spread of these outbreaks within Bulgaria. Both methods indicate two separate incursions, one restricted to the northeastern region of Dobrich, and another largely restricted to Central and Eastern Bulgaria including places such as Plovdiv, Sliven and Stara Zagora, as well as one virus from the Western region of Vidin. Both outbreaks likely originate from different European 2.3.4.4b virus ancestors circulating in 2017. The viruses were likely introduced by wild birds or poultry trade links in 2017 and have continued to circulate, but due to lack of contemporaneous sampling and sequences from wild bird viruses in Bulgaria, the precise route and timing of introduction cannot be determined. Analysis of whole genomes indicates a complete lack of reassortment in all segments but the matrix protein gene (MP), which presents as multiple smaller clusters associated with different European 2.3.4.4b viruses. Ancestral reconstruction of host states of the hemagglutinin (HA) gene of viruses involved in the outbreaks suggests that transmission is driven by domestic ducks into galliform poultry. Thus, according to present evidence, we suggest the surveillance of domestic ducks as they are an epidemiologically relevant species for subclinical infection. Monitoring the spread due to movement between farms within regions and links to poultry production systems in European countries can help to predict and prevent future outbreaks. The 2.3.4.4b lineage which caused the largest recorded poultry epidemic in Europe continues to circulate, and the risk of further transmission by wild birds during migration remains.

Emerging investigator series: use of behavioural endpoints in the regulation of chemicals

Interest in behavioural ecotoxicology is growing, partly due to technological and computational advances in recording behaviours but also because of improvements of detection capacity facilitating reporting effects at environmentally relevant concentrations. The peer-reviewed literature now contains studies investigating the effects of chemicals, including pesticides and pharmaceuticals, on migration, dispersal, aggression, sociability, reproduction, feeding and anti-predator behaviours in vertebrates and invertebrates. To understand how behavioural studies could be used in regulatory decision-making we: (1) assessed the legal obstacles to using behavioural endpoints in EU chemicals regulation; (2) analysed the known cases of use of behavioural endpoints in EU chemicals regulation; and (3) provided examples of behavioural endpoints of relevance for population level effects. We conclude that the only legal obstacle to the use of behavioural endpoints in EU chemicals regulation is whether an endpoint is considered to be relevant at the population level or not. We also conclude that ecotoxicity studies investigating behavioural endpoints are occasionally used in the EU chemicals regulation, and underscore that behavioural endpoints can be relevant at the population level. To improve the current use of behavioural studies in regulatory decision-making contribution from all relevant stakeholders is required. We have the following recommendations: (1) researchers should conduct robust, well-designed and transparent studies that emphasize the relevance of the study for regulation of chemicals; (2) editors and scientific journals should promote detailed, reliable and clearly reported studies; (3) regulatory agencies and the chemical industry need to embrace new behavioural endpoints of relevance at the population level.

No evidence of avian influenza antibodies in two species of raptor nestlings inhabiting Norway

Background

Since 2016, incursions of highly pathogenic avian influenza virus (HPAIV) H5N8 clade 2.3.4.4b have caused unprecedented clinical signs and mortality in white-tailed eagles (WTE; Haliaeetus albicilla) across Europe and have been found to be infecting other raptor species, such as the northern goshawk (NG; Accipiter gentilis). Before this study, no screening of Norwegian raptors had been undertaken.

Results

Plasma samples from 43 white-tailed eagle and 29 northern goshawk nestlings, from several locations across Norway were screened for antibodies to avian influenza viruses. No antibodies, and thus, no evidence of AIV exposure, were found in these Norwegian raptors. No clinical signs of AIV were observed in 43 white tailed eagles and 29 northern goshawks.

Conclusions

There are currently no indications that white-tailed eagles and northern goshawks inhabiting Norway are threatened by the recent HPAIV outbreaks in other areas of Europe. Ongoing monitoring should, however, be maintained to detect potential future outbreaks.

Adlhoch C, Kuiken T, Monne I, Mulatti P, Smietanka K, Staubach C, Guajardo IM, Baldinelli F. Avian influenza overview November 2018 - February 2019

No human infections due to highly pathogenic avian influenza (HPAI) A(H5N8) or A(H5N6) viruses ‐ detected in wild birds and poultry outbreaks in Europe ‐ have been reported so far and the risk of zoonotic transmission to the general public in Europe is considered very low. Between 16 November 2018 and 15 February 2019, two HPAI A(H5N8) outbreaks in poultry establishments in Bulgaria, two HPAI A(H5N6) outbreaks in wild birds in Denmark and one low pathogenic avian influenza (LPAI) A(H5N3) in captive birds in the Netherlands were reported in the European Union (EU). Genetic characterisation of the HPAI A(H5N6) viruses reveals that they cluster with the A(H5N6) viruses that have been circulating in Europe since December 2017. The wild bird species involved were birds of prey and were likely infected due to hunting or scavenging infected wild waterfowl. However, HPAI virus was not detected in other wild birds during this period. Outside the EU, two HPAI outbreaks were reported in poultry during the reporting period from western Russia. Sequence information on an HPAI A(H5N6) virus found in a common gull in western Russia in October 2018 suggests that the virus clusters within clade 2.3.4.4c and is closely related to viruses that transmitted zoonotically in China. An increasing number of outbreaks in poultry and wild birds in Asia, Africa and the Middle East was observed during the time period for this report. Currently there is no evidence of a new HPAI virus incursion from Asia into Europe. However, passive surveillance systems may not be sensitive enough if the prevalence or case fatality in wild birds is very low. Nevertheless, it is important to encourage and maintain a certain level of passive surveillance in Europe testing single sick or dead wild birds and birds of prey as they may be sensitive sentinel species for the presence of HPAI virus in the environment. A well‐targeted active surveillance might complement passive surveillance to collect information on HPAI infectious status of apparently healthy wild bird populations.

Assessment of low pathogenic avian influenza virus transmission via raw poultry meat and raw table eggs

A rapid qualitative assessment has been done by performing a theoretical analysis on the transmission of low pathogenic avian influenza (LPAI) via fresh meat from poultry reared or kept in captivity for the production of meat (raw poultry meat) or raw table eggs. A predetermined transmission pathway followed a number of steps from a commercial or non-commercial poultry establishment within the EU exposed to LPAI virus (LPAIV) to the onward virus transmission to animals and humans. The combined probability of exposure and subsequent LPAIV infection via raw poultry meat containing LPAIV is negligible for commercial poultry and humans exposed via consumption whereas it is very unlikely for non-commercial poultry, wild birds and humans exposed via handling and manipulation. The probability of LPAIV transmission from an individual infected via raw poultry meat containing LPAIV is negligible for commercial poultry and humans, whereas it is very unlikely for non-commercial poultry and wild birds. The combined probability of exposure and subsequent LPAIV infection via raw table eggs containing LPAIV is negligible for commercial poultry and humans and extremely unlikely to negligible for non-commercial poultry and wild birds. The probability of LPAIV transmission from an individual infected via raw table eggs containing LPAIV is negligible for commercial poultry and humans and very unlikely to negligible for non-commercial poultry and wild birds. Although the presence of LPAIV in raw poultry meat and table eggs is very unlikely to negligible, there is in general a high level of uncertainty on the estimation of the subsequent probabilities of key steps of the transmission pathways for poultry and wild birds, mainly due to the limited number of studies available, for instance on the viral load required to infect a bird via raw poultry meat or raw table eggs containing LPAIV.

Adlhoch C, Kuiken T, Mulatti P, Smietanka K, Staubach C, Muñoz Guajardo I, Amato L, Baldinelli F. Avian influenza overview May - August 2018

Between 16 May and 15 August 2018, three highly pathogenic avian influenza (HPAI) A(H5N8) outbreaks in poultry establishments and three HPAI A(H5N6) outbreaks in wild birds were reported in Europe. Three low pathogenic avian influenza (LPAI) outbreaks were reported in three Member States. Few HPAI and LPAI bird cases have been detected in this period of the year, in accordance with the seasonal expected pattern of LPAI and HPAI. There is no evidence to date that HPAI A(H5N8) and A(H5N6) viruses circulating in Europe have caused any human infections. The risk of zoonotic transmission to the general public in Europe is considered to be very low. Several HPAI outbreaks in poultry were reported during this period from Russia. The presence of the A(H5N2) and A(H5N8) viruses in parts of Russia connected with fall migration routes of wild birds is of concern for possible introduction and spread with wild birds migrating to the EU. Although few AI outbreaks were observed in Africa, Asia and the Middle East during the reporting period, the probability of AI virus introductions from non‐EU countries via wild birds particularly via the north‐eastern route from Russia is increasing, as the fall migration of wild birds will start in the coming weeks. Further, the lower temperatures in autumn and winter may facilitate the environmental survival of avian influenza viruses potentially introduced to Europe.