Caught Right on the Spot: Isolation and Characterization of Clade 2.3.4.4b H5N8 High Pathogenicity Avian Influenza Virus from a Common Pochard (Aythya ferina) Being Attacked by a Peregrine Falcon (Falco peregrinus)

We isolated a high pathogenicity avian influenza (HPAI) virus from a common pochard (Aythya ferina) that was being attacked by a bird of prey in South Korea in December 2020. Genetic analyses indicated that the isolate was closely related to the clade 2.3.4.4b H5N8 HPAI viruses found in South Korea and Japan during the winter season of 2020-2021. The histopathological examination revealed multifocal necrotizing inflammation in the liver, kidney, and spleen. Viral antigens were detected in the liver, kidney, spleen, trachea, intestine, and pancreas, indicating the HPAI virus caused a systemic infection. The presence of immunoreactivity for the viral antigen was observed in the cells involved in multifocal necrotic inflammation. Notably, epitheliotropic-positive patterns were identified in the epithelial cells of the trachea, mucosal epithelium of the intestine, and ductular epithelium of the pancreas. These findings provide direct evidence supporting the possibility of HPAI transmission from infected waterfowl to predators.

Genome sequences of haemagglutinin cleavage site predict the pathogenicity phenotype of avian influenza virus: statistically validated data for facilitating rapid declarations and reducing reliance on in vivo testing

ABSTRACTBased on the pathogenicity in chickens, most H1-H16 avian influenza viruses (AIV) cause mild diseases, whereas some of the H5 and H7 AI viruses cause severe, systemic disease. The number of basic amino acids in the haemagglutinin (HA) cleavage site of AIV plays a critical role in pathogenicity. As we gain a greater understanding of the molecular mechanisms of pathogenicity, genome sequencing of the HA0 cleavage site has assumed a greater role in assessment of the potential pathogenicity of H5 and H7 viruses. We validated the use of HA cleavage site motif analysis by comparing molecular pathotyping data against experimental in vivo (intravenous pathogenicity index [IVPI] and lethality) data for determination of both low pathogenicity and high pathogenicity AI virus declaration with the goal of expediting pathotype confirmation and further reducing the reliance on in vivo testing. Our data provide statistical support to the continued use of molecular determination of pathotype for AI viruses based on the HA cleavage site sequence in the absence of an in vivo study determination. This approach not only expedites the declaration process of highly pathogenic AIV (HPAIV) but also reduces the need for experimental in vivo testing of H5 and H7 viruses.

Diverse infectivity, transmissibility, and pathobiology of clade 2.3.4.4 H5Nx highly pathogenic avian influenza viruses in chickens

Clade 2.3.4.4 Eurasian lineage H5Nx highly pathogenic avian influenza virus (HPAIV) has become the globally dominant clade and caused global outbreaks since 2014. The clade 2.3.4.4 viruses have evolved into eight hemagglutinin subgroups (2.3.4.4a-h). In this study, we evaluated the infectivity, pathobiology, and transmissibility of seven clade 2.3.4.4 viruses (two 2.3.4.4a, two 2.3.4.4b, one 2.3.4.4c and two 2.3.4.4e) in chickens. The two clade 2.3.4.4e viruses caused 100% mortality and transmissibility in chickens. However, clade 2.3.4.4a and c viruses showed 80-90% mortality and 67% transmissibility. Clade 2.3.4.4b viruses showed 100% mortality, but no transmission to co-housed chickens was observed based on lack of seroconversion. All the infected chickens died showing systemic infection, irrespective of subgroup. The results highlight that all the clade 2.3.4.4 HPAIVs used in this study caused high mortality in infected chickens, but the transmissibility of the viruses in chickens was variable in contrast to that of previous Eurasian-lineage H5N1 HPAIVs. Changes in the pathogenicity and transmissibility of clade 2.3.4.4 HPAIVs warrant careful monitoring of the viruses to establish effective control strategies.

Pathogenicity in Chickens and Turkeys of a 2021 United States H5N1 Highly Pathogenic Avian Influenza Clade 2.3.4.4b Wild Bird Virus Compared to Two Previous H5N8 Clade 2.3.4.4 Viruses

Highly pathogenic avian influenza viruses (HPAIVs) of subtype H5 of the Gs/GD/96 lineage remain a major threat to poultry due to endemicity in wild birds. H5N1 HPAIVs from this lineage were detected in 2021 in the United States (U.S.) and since then have infected many wild and domestic birds. We evaluated the pathobiology of an early U.S. H5N1 HPAIV (clade 2.3.4.4b, 2021) and two H5N8 HPAIVs from previous outbreaks in the U.S. (clade 2.3.4.4c, 2014) and Europe (clade 2.3.4.4b, 2016) in chickens and turkeys. Differences in clinical signs, mean death times (MDTs), and virus transmissibility were found between chickens and turkeys. The mean bird infective dose (BID50) of the 2021 H5N1 virus was approximately 2.6 log10 50% embryo infective dose (EID50) in chickens and 2.2 log10 EID50 in turkeys, and the virus transmitted to contact-exposed turkeys but not chickens. The BID50 for the 2016 H5N8 virus was also slightly different in chickens and turkeys (4.2 and 4.7 log10 EID50, respectively); however, the BID50 for the 2014 H5N8 virus was higher for chickens than turkeys (3.9 and ~0.9 log10 EID50, respectively). With all viruses, turkeys took longer to die (MDTs of 2.6-8.2 days for turkeys and 1-4 days for chickens), which increased the virus shedding period and facilitated transmission to contacts.

H5N1 highly pathogenic avian influenza clade 2.3.4.4b in wild and domestic birds: Introductions into the United States and reassortments, December 2021-April 2022

Highly pathogenic avian influenza viruses (HPAIVs) of the A/goose/Guangdong/1/1996 lineage H5 clade 2.3.4.4b continue to have a devastating effect on domestic and wild birds. Full genome sequence analyses using 1369 H5N1 HPAIVs detected in the United States (U.S.) in wild birds, commercial poultry, and backyard flocks from December 2021 to April 2022, showed three phylogenetically distinct H5N1 virus introductions in the U.S. by wild birds. Unreassorted Eurasian genotypes A1 and A2 entered the Northeast Atlantic states, whereas a genetically distinct A3 genotype was detected in Alaska. The A1 genotype spread westward via wild bird migration and reassorted with North American wild bird avian influenza viruses. Reassortments of up to five internal genes generated a total of 21 distinct clusters; of these, six genotypes represented 92% of the HPAIVs examined. By phylodynamic analyses, most detections in domestic birds were shown to be point-source transmissions from wild birds, with limited farm-to-farm spread.

Prediction of highly pathogenic avian influenza vaccine efficacy in chickens by comparison of in vitro and in vivo data: A meta-analysis and systematic review

Vaccines for avian influenza (AI) can protect poultry against disease, mortality, and virus transmission. Numerous factors, including: vaccine platform, immunogenicity, and relatedness to the field strain, are known to be important to achieving optimal AI vaccine efficacy. To better understand how these factors contribute to vaccine protection, a systematic meta-analysis was conducted to evaluate efficacy data for vaccines in chickens challenged with highly pathogenic (HP) AI. Data from a total of 120 individual trials from 25 publications were selected and evaluated. Two vaccine criteria were evaluated for their effects on two metrics of protection. The vaccine criteria were: 1) the relatedness of the vaccine antigen and challenge strain in the hemagglutinin 1 domain (HA1) protein sequence; 2) vaccine-induced antibody titers to the challenge virus (VIAC). The metrics of protection were: A) survival of vaccinated chickens vs unvaccinated controls; and B) reduction in oral virus-shedding by vaccinated vs unvaccinated controls 2-4 days post challenge. Three vaccine platforms were evaluated: oil-adjuvanted inactivated whole AI virus, recombinant herpes virus of turkeys (rHVT) vectored, and a non-replicating alpha-virus vectored RNA particle (RP) vaccine. Higher VIAC correlated with greater reduction of virus-shed and vaccine efficacy by all vaccine platforms. Both higher HA1 relatedness and higher VIAC using challenge virus as antigen correlated with better survival by inactivated vaccines and rHVT-vectored vaccines. However, rHVT-vectored and RP based vaccines were more tolerant of variation in the HA1; the relatedness of the HA1 of the vaccine and challenge virus did not significantly correlate with survival with rHVT-vectored vaccines. Protection was achieved with the lowest aa similarity for which there was data, 90-93 % for rHVT vaccines and 88 % for the RP vaccine.

Efficacy of multivalent recombinant herpesvirus of turkey vaccines against high pathogenicity avian influenza, infectious bursal disease, and Newcastle disease viruses

Vaccines are an essential tool for the control of viral infections in domestic animals. We generated recombinant vector herpesvirus of turkeys (vHVT) vaccines expressing computationally optimized broadly reactive antigen (COBRA) H5 of avian influenza virus (AIV) alone (vHVT-AI) or in combination with virus protein 2 (VP2) of infectious bursal disease virus (IBDV) (vHVT-IBD-AI) or fusion (F) protein of Newcastle disease virus (NDV) (vHVT-ND-AI). In vaccinated chickens, all three vHVT vaccines provided 90-100% clinical protection against three divergent clades of high pathogenicity avian influenza viruses (HPAIVs), and significantly decreased number of birds and oral viral shedding titers at 2 days post-challenge compared to shams. Four weeks after vaccination, most vaccinated birds had H5 hemagglutination inhibition antibody titers, which significantly increased post-challenge. The vHVT-IBD-AI and vHVT-ND-AI vaccines provided 100% clinical protection against IBDVs and NDV, respectively. Our findings demonstrate that multivalent HVT vector vaccines were efficacious for simultaneous control of HPAIV and other viral infections.

Reducing zoonotic avian influenza transmission at household poultry slaughter using a behaviour change tool for limited literacy audiences

Human infections in Egypt with highly pathogenic avian influenza (HPAI) likely due to airborne transmission of HPAI virus (HPAIV) during home slaughter of poultry predominately affect women and children, who are the primary caregivers of household poultry. This study developed a safe contained poultry slaughter procedure to reduce airborne HPAIV and zoonotic infections and simultaneously created an educational outreach tool for teaching the modified procedure. The tool designed for limited literacy audiences used two illustrated posters and handouts for teaching the safe contained poultry slaughter procedure. The posters were developed with advice of animal health professionals and then refined by target audience women's focus groups. These women's focus groups proved to be the critical step for assuring the understanding, acceptance, effectiveness and accuracy of the outreach tool. The safe contained poultry slaughter procedure was designed to be low or no cost, sustainable by using a universal implement found in village households and designed as a minor variation of standard poultry halal slaughter. It was crafted to be culturally appropriate and religiously acceptable.

Optimizing sample collection methods for detection of respiratory viruses in poultry housing environments

Viral respiratory diseases, such as avian influenza, Newcastle disease, infectious bronchitis, and infectious laryngotracheitis, have considerable negative economic implications for poultry. Ensuring the virus-free status of a premises by environmental sampling after cleaning and disinfection is essential for lifting a quarantine and/or safely restocking the premises following an outbreak. The objectives of this study were to identify optimal sample collection devices and to determine the locations in poultry housing which are best for poultry respiratory virus sample collection. Chickens exposed to infectious bronchitis virus, which was used as a representative virus for enveloped poultry respiratory viruses, were housed in floor-pens in either a curtain-sided wood framed house or a cement block house. Foam swabs, cellulose sponges, polyester swabs, dry cotton gauze and pre-moistened cotton gauze were evaluated for comparative efficiency in recovering viral RNA. Cotton gauze pre-moistened with the viral transport media had the highest sensitivity among the devices (wood-framed house: 78% positive, geometric mean titer [GMT] of 2.6 log₁₀ 50% egg infectious doses [EID₅₀ ] equivalents/ml; cement-block houses: 55% positive, GMT of 1.7 log₁₀ EID₅₀ equivalents/ml). Targeting virus deposition sites is also crucial for efficient virus elimination procedures and subsequent testing, therefore 10 locations within the houses were compared for virus detection. In both housing types the highest viral RNA loads were recovered from the top of drinker lines within the pen. Places the chickens could contact directly (e.g., feeder rim) or were contacted by caretaker feet (hallway floor) also yielded higher levels of viral RNA more consistently. These results will facilitate the establishment of efficient environmental sampling procedures for respiratory viruses of poultry. This article is protected by copyright. All rights reserved.

Transmission Dynamics of Low Pathogenicity Avian Influenza (H2N2) Viruses in Live Bird Markets of the Northeast United States of America, 2013-2019

Live bird market (LBM) surveillance was conducted in the Northeast United States (US) to monitor for the presence of avian influenza viruses (AIV) in domestic poultry and market environments. A total of 384 H2N2 low pathogenicity AIV (LPAIV) isolated from active surveillance efforts in the LBM system of New York, Connecticut, Rhode Island, New Jersey, Pennsylvania, and Maryland during 2013–2019 were included in this analysis. Comparative phylogenetic analysis showed that a wild-bird-origin H2N2 virus may have been introduced into the LBMs in Pennsylvania and independently evolved since March 2012 followed by spread to LBMs in New York City during late 2012–early 2013. LBMs in New York state played a key role in the maintenance and dissemination of the virus to LBMs in the Northeast US including reverse spread to Pennsylvania LBMs. The frequent detections in the domestic ducks and market environment with viral transmissions between birds and environment possibly led to viral adaptation and circulation in domestic gallinaceous poultry in LBMs, suggesting significant roles of domestic ducks and contaminated LBM environment as reservoirs in maintenance and dissemination of H2N2 LPAIV.

Low-pathogenicity influenza viruses replicate differently in laughing gulls and mallards

Wild aquatic birds are natural reservoirs of low-pathogenicity avian influenza viruses (LPAIVs). Laughing gulls inoculated with four gull-origin LPAIVs (H7N3, H6N4, H3N8, and H2N3) had a predominate respiratory infection. By contrast, mallards inoculated with two mallard-origin LPAIVs (H5N6 and H4N8) became infected and had similar virus titers in oropharyngeal (OP) and cloacal (CL) swabs. The trend toward predominate OP shedding in gulls suggest a greater role of direct bird transmission in maintenance, whereas mallards shedding suggests importance of fecal-oral transmission through water contamination. Additional infectivity and pathogenesis studies are needed to confirm this replication difference for LPAI viruses in gulls.

Erratum: Genetic Evolution and Transmission Dynamics of Clade 2.3.2.1a Highly Pathogenic Avian Influenza A/H5N1 Viruses in Bangladesh

[This corrects the article DOI: 10.1093/ve/veaa046.].

Efficacy of two vaccines against recent emergent antigenic variants of clade 2.3.2.1a highly pathogenic avian influenza viruses in Bangladesh

H5N1 highly pathogenic avian influenza viruses (HPAIVs) have caused outbreaks in poultry in Bangladesh since 2007. While clade 2.2.2 and 2.3.4.2 HPAIVs have not been detected since 2012, clade 2.3.2.1a viruses have caused continuous outbreaks since 2012 despite the use of vaccines. In this study, we evaluated the efficacy of two H5 vaccines licensed in Bangladesh, RE-6 inactivated vaccine, and a recombinant herpesvirus of turkeys vaccine with an H5 insert (rHVT-H5), for protection against recent field viruses in chickens. We selected three viruses for efficacy tests (A/chicken/Bangladesh/NRL-AI-3237/2017, A/crow/Bangladesh/NRL-AI-8471/2017 and A/chicken/Bangladesh/NRL-AI-8323/2017) from 36 H5 viruses isolated from Bangladesh between 2016 and 2018 by comparing the amino acid sequences at five antigenic sites (A-E) and analyzing hemagglutination inhibition (HI) titers with reference antisera. The RE-6 and rHVT-H5 vaccines both conferred 80-100% clinical protection (i.e. reduced morbidity and mortality) against the three challenge viruses with no significant differences in protection. In addition, both vaccines significantly decreased viral shedding from infected chickens as compared to challenge control chickens. Based on these metrics, the current licensed H5 vaccines protected chickens against the recent field viruses. However, the A/crow/Bangladesh/NRL-AI-8471/2017 virus exhibited antigenic divergence including: several unique amino acid changes in antigenic epitope sites A and B and was a serological outlier in cross HI tests as visualized on the antigenic map. The continuing emergence of such antigenic variants which could alter the dominant antigenicity of field viruses should be continuously monitored and vaccines should be updated if field efficacy declines.

Efficacy of recombinant Marek's disease virus vectored vaccines with computationally optimized broadly reactive antigen (COBRA) hemagglutinin insert against genetically diverse H5 high pathogenicity avian influenza viruses

The genetic and antigenic drift associated with the high pathogenicity avian influenza (HPAI) viruses of Goose/Guangdong (Gs/GD) lineage and the emergence of vaccine-resistant field viruses underscores the need for a broadly protective H5 influenza A vaccine. Here, we tested experimental vector herpesvirus of turkey (vHVT)-H5 vaccines containing either wild-type clade 2.3.4.4A-derived H5 inserts or computationally optimized broadly reactive antigen (COBRA) inserts with challenge by homologous and genetically divergent H5 HPAI Gs/GD lineage viruses in chickens. Direct assessment of protection was confirmed for all the tested constructs, which provided clinical protection against the homologous and heterologous H5 HPAI Gs/GD challenge viruses and significantly decreased oropharyngeal shedding titers compared to the sham vaccine. The cross reactivity was assessed by hemagglutinin inhibition (HI) and focus reduction assay against a panel of phylogenetically and antigenically diverse H5 strains. The COBRA-derived H5 inserts elicited antibody responses against antigenically diverse strains, while the wild-type-derived H5 vaccines elicited protection mostly against close antigenically related clades 2.3.4.4A and 2.3.4.4D viruses. In conclusion, the HVT vector, a widely used replicating vaccine platform in poultry, with H5 insert provides clinical protection and significant reduction of viral shedding against homologous and heterologous challenge. In addition, the COBRA-derived inserts have the potential to be used against antigenically distinct co-circulating viruses and future drift variants.

Pathobiological Origins and Evolutionary History of Highly Pathogenic Avian Influenza Viruses

High-pathogenicity avian influenza (HPAI) viruses have arisen from low-pathogenicity avian influenza (LPAI) viruses via changes in the hemagglutinin proteolytic cleavage site, which include mutation of multiple nonbasic to basic amino acids, duplication of basic amino acids, or recombination with insertion of cellular or viral amino acids. Between 1959 and 2019, a total of 42 natural, independent H5 (n = 15) and H7 (n = 27) LPAI to HPAI virus conversion events have occurred in Europe (n = 16), North America (n = 9), Oceania (n = 7), Asia (n = 5), Africa (n = 4), and South America (n = 1). Thirty-eight of these HPAI outbreaks were limited in the number of poultry premises affected and were eradicated. However, poultry outbreaks caused by A/goose/Guangdong/1/1996 (H5Nx), Mexican H7N3, and Chinese H7N9 HPAI lineages have continued. Active surveillance and molecular detection and characterization efforts will provide the best opportunity for early detection and eradication from domestic birds.

Lack of Susceptibility to SARS-CoV-2 and MERS-CoV in Poultry

We challenged chickens, turkeys, ducks, quail, and geese with severe acute respiratory syndrome coronavirus 2 or Middle East respiratory syndrome coronavirus. We observed no disease and detected no virus replication and no serum antibodies. We concluded that poultry are unlikely to serve a role in maintenance of either virus.

Low Pathogenicity Avian Influenza (H5N2) Viruses, Dominican Republic

Low pathogenicity avian influenza (H5N2) virus was detected in poultry in the Dominican Republic in 2007 and re-emerged in 2017. Whole-genome sequencing and phylogenetic analysis show introduction of an H5N2 virus lineage from Mexico into poultry in the Dominican Republic, then divergence into 3 distinct genetic subgroups during 2007–2019.

Highly Pathogenic Avian Influenza A(H7N3) Virus in Poultry, United States, 2020

An outbreak of low-pathogenicity avian influenza A(H7N3) virus of North American wild bird lineage occurred on commercial turkey farms in North Carolina and South Carolina, USA, during March-April 2020. The virus mutated to the highly pathogenic form in 1 house on 1 farm via recombination with host 28S rRNA.

H7N1 Low Pathogenicity Avian Influenza Viruses in Poultry in the United States During 2018

Here, we report three detections of H7N1 low pathogenicity avian influenza viruses (LPAIV) from poultry in Missouri (n = 2) and Texas (n = 1) during February and March 2018. Complete genome sequencing and comparative phylogenetic analysis suggest that the H7 LPAIV precursor viruses were circulating in wild birds in North America during the fall and winter of 2017 and spilled over into domestic poultry in Texas and Missouri independently during the spring of 2018.

Spotlight on avian pathology: can we reduce the pandemic threat of H9N2 avian influenza to human and avian health?

COVID-19 should be a "call to arms" for the poultry industry to reassess containment of the H9N2 subtype of low pathogenicity avian influenza viruses. Strains of this virus are a human pandemic threat and a severe economic burden on poultry production. Over the past 20 years they have spread throughout Asia, Africa, Middle East and parts of Europe. As a global industry, a critical need is to re-imagine production and marketing chains, especially in low and middle-income countries, where the structure of much of the industry facilitates virus transmission, especially, but not only, in improperly managed live poultry markets and related value chains. Better, appropriately matched vaccines are needed to support this process but such vaccines cannot, alone, overcome the existing defects in biosecurity, including high farm densities. None of this will occur unless the threat posed by this virus to global health security is recognized.

Genetic evolution and transmission dynamics of clade 2.3.2.1a highly pathogenic avian influenza A/H5N1 viruses in Bangladesh

Asian lineage A/H5N1 highly pathogenic avian influenza viruses (HPAIVs) have been responsible for continuous outbreaks in Bangladesh since 2007. Although clades 2.2.2 and 2.3.4.2 HPAIVs have disappeared since poultry vaccination was introduced in 2012, clade 2.3.2.1a viruses have continued to be detected in Bangladesh. In this study, we identified A/H9N2 (n = 15), A/H5N1 (n = 19), and A/H5N1-A/H9N2 (n = 18) mixed viruses from live bird markets, chicken farms, and wild house crows (Corvus splendens) in Bangladesh from 2016 to 2018. We analyzed the genetic sequences of the H5 HPAIVs, to better understand the evolutionary history of clade 2.3.2.1a viruses in Bangladesh. Although seven HA genetic subgroups (B1-B7) and six genotypes (G1, G1.1, G1.2, G2, G2.1, and G2.2) have been identified in Bangladesh, only subgroup B7 and genotypes G2, G2.1, and G2.2 were detected after 2016. The replacement of G1 genotype by G2 in Bangladesh was possibly due to vaccination and viral competition in duck populations. Initially, genetic diversity decreased after introduction of vaccination in 2012, but in 2015, genetic diversity increased and was associated with the emergence of genotype G2. Our phylodynamic analysis suggests that domestic Anseriformes, including ducks and geese, may have played a major role in persistence, spread, evolution, and genotype replacement of clade 2.3.2.1a HPAIVs in Bangladesh. Thus, improvements in biosecurity and monitoring of domestic Anseriformes are needed for more effective control of HPAI in Bangladesh.

Live bird markets as evolutionary epicentres of H9N2 low pathogenicity avian influenza viruses in Korea

Live bird markets (LBMs) in Korea have been recognized as a reservoir, amplifier, and source of avian influenza viruses (AIVs); however, little was known about the role of LBMs in the epidemiology of AIVs in Korea until recently. Through 10 years of surveillance (2006–2016) we have isolated and sequenced H9N2 viruses in Korean LBMs. To understand how H9N2 evolves and spreads in Korea, a statistical Bayesian phylogenetic model was used. Phylogenetic analysis suggests that three separate introductions of progenitor gene pools, Korean domestic duck-origin and two wild aquatic bird-origin AIVs, contributed to the generation of the five genotypes of H9N2 viruses in Korea. Phylogenetic reconstruction of ecological states infer that the LBMs are where chickens become infected with the virus, with domestic ducks playing a major role in the transmission and evolution of the H9N2 viruses. Three increases in the genetic diversity of H9N2 viruses were observed and coincided with transitions in host species and the locations (domestic farm, LBM, slaughterhouse, and wild aquatic bird habitat) where the viruses were isolated, accompanying genetic reassortment. Following the introduction of a wild aquatic bird-origin AIVs in 2008, six genes of the Korean lineage H9N2 virus were replaced with genes originating from wild aquatic birds, and viruses with this new genotype became predominant in Korean LBMs.

Pandemic potential of highly pathogenic avian influenza clade 2.3.4.4 A(H5) viruses

The panzootic caused by A/goose/Guangdong/1/96‐lineage highly pathogenic avian influenza (HPAI) A(H5) viruses has occurred in multiple waves since 1996. From 2013 onwards, clade 2.3.4.4 viruses of subtypes A(H5N2), A(H5N6), and A(H5N8) emerged to cause panzootic waves of unprecedented magnitude among avian species accompanied by severe losses to the poultry industry around the world. Clade 2.3.4.4 A(H5) viruses have expanded in distinct geographical and evolutionary pathways likely via long distance migratory bird dispersal onto several continents and by poultry trade among neighboring countries. Coupled with regional circulation, the viruses have evolved further by reassorting with local viruses. As of February 2019, there have been 23 cases of humans infected with clade 2.3.4.4 H5N6 viruses, 16 (70%) of which had fatal outcomes. To date, no HPAI A(H5) virus has caused sustainable human‐to‐human transmission. However, due to the lack of population immunity in humans and ongoing evolution of the virus, there is a continuing risk that clade 2.3.4.4 A(H5) viruses could cause an influenza pandemic if the ability to transmit efficiently among humans was gained. Therefore, multisectoral collaborations among the animal, environmental, and public health sectors are essential to conduct risk assessments and develop countermeasures to prevent disease and to control spread. In this article, we describe an assessment of the likelihood of clade 2.3.4.4 A(H5) viruses gaining human‐to‐human transmissibility and impact on human health should such human‐to‐human transmission occur. This structured analysis assessed properties of the virus, attributes of the human population, and ecology and epidemiology of these viruses in animal hosts.

Biosafety risk assessment for production of candidate vaccine viruses to protect humans from zoonotic highly pathogenic avian influenza viruses

A major lesson learned from the public health response to the 2009 H1N1 pandemic was the need to shorten the vaccine delivery timeline to achieve the best pandemic mitigation results. A gap analysis of previous pre-pandemic vaccine development activities identified possible changes in the Select Agent exclusion process that would maintain safety and shorten the timeline to develop candidate vaccine viruses (CVVs) for use in pandemic vaccine manufacture. Here, we review the biosafety characteristics of CVVs developed in the past 15 years to support a shortened preparedness timeline for A(H5) and A(H7) subtype highly pathogenic avian influenza (HPAI) CVVs. Extensive biosafety experimental evidence supported recent changes in the implementation of Select Agent regulations that eliminated the mandatory chicken pathotype testing requirements and expedited distribution of CVVs to shorten pre-pandemic and pandemic vaccine manufacturing by up to 3 weeks.

Agricultural and geographic factors shaped the North American 2015 highly pathogenic avian influenza H5N2 outbreak

The 2014-2015 highly pathogenic avian influenza (HPAI) H5NX outbreak represents the largest and most expensive HPAI outbreak in the United States to date. Despite extensive traditional and molecular epidemiological studies, factors associated with the spread of HPAI among midwestern poultry premises remain unclear. To better understand the dynamics of this outbreak, 182 full genome HPAI H5N2 sequences isolated from commercial layer chicken and turkey production premises were analyzed using evolutionary models able to accommodate epidemiological and geographic information. Epidemiological compartmental models embedded in a phylogenetic framework provided evidence that poultry type acted as a barrier to the transmission of virus among midwestern poultry farms. Furthermore, after initial introduction, the propagation of HPAI cases was self-sustainable within the commercial poultry industries. Discrete trait diffusion models indicated that within state viral transitions occurred more frequently than inter-state transitions. Distance and sample size were very strongly supported as associated with viral transition between county groups (Bayes Factor > 30.0). Together these findings indicate that the different types of midwestern poultry industries were not a single homogenous population, but rather, the outbreak was shaped by poultry industries and geographic factors.

Laboratory Methods for Assessing and Licensing Influenza Vaccines for Poultry

Avian influenza (AI) vaccines for poultry are based on hemagglutinin (HA) proteins, and protection is specific to the subtype. An estimated 313 billion doses have been used between 2002 and 2018 for high pathogenicity AI control. No universal vaccines are currently available. The majority of AI vaccines are inactivated whole influenza viruses that are grown in embryonating chicken eggs, emulsified in oil adjuvant systems, and injected subcutaneously or intramuscularly. Live virus-vectored vaccines such as recombinant viruses of fowl pox, Newcastle disease, and herpesvirus of turkeys containing inserts of AI virus HA genes have been used on a more limited basis. Also, vaccines have been licensed or registered based on baculovirus and defective replicating alphavirus (RNA particles) expressing HA protein or DNA vaccine with HA gene insert. In studies to evaluate vaccine efficacy and potency, the protocol design and its implementation should address the biosafety level needed for the work, provide information required for approval by Institutional Biosafety and Animal Care Committees, contain information on seed strain selection, provide needed information on animal subjects and their relevant parameters, and address the selection and use of challenge viruses. Various metrics have been used to directly measure vaccine-induced protection, including prevention of death, clinical signs, and lesions; prevention of decreases in egg production and alterations in egg quality; quantification of the reduction in virus replication and shedding from the respiratory tract and gastrointestinal tracts; and prevention of contact transmission in in vivo poultry experiments. In addition, indirect measures of vaccine potency and protection have been developed and validated against the direct measures and include serological assays in vaccinated poultry and the assessment of the content of HA antigen in the vaccine. These indirect assessments of protection are useful in determining if vaccine batches have a consistent ability to protect. For adequate potency, vaccines should contain 50 mean protective doses of antigen per dose, which corresponds to 0.3-7.8 μg of HA protein in inactivated vaccines, depending on immunogenicity and antigenic relatedness of individual seed strains.

Protection of White Leghorn chickens by recombinant fowlpox vector vaccine with an updated H5 insert against Mexican H5N2 avian influenza viruses

Despite decades of vaccination, surveillance, and biosecurity measures, H5N2 low pathogenicity avian influenza (LPAI) virus infections continue in Mexico and neighboring countries. One explanation for tenacity of H5N2 LPAI in Mexico is the antigenic divergence of circulating field viruses compared to licensed vaccines due to antigenic drift. Our phylogenetic analysis indicates that the H5N2 LPAI viruses circulating in Mexico and neighboring countries since 1994 have undergone antigenic drift away from vaccine seed strains. Here we evaluated the efficacy of a new recombinant fowlpox virus vector containing an updated H5 insert (rFPV-H5/2016), more relevant to the current strains circulating in Mexico. We tested the vaccine efficacy against a closely related subcluster 4 Mexican H5N2 LPAI (2010 H5/LP) virus and the historic H5N2 HPAI (1995 H5/HP) virus in White Leghorn chickens. The rFPV-H5/2016 vaccine provided hemagglutinin inhibition (HI) titers pre-challenge against viral antigens from both challenge viruses in almost 100% of the immunized birds, with no differences in number of birds seroconverting or HI titers among all tested doses (1.5, 2.0, and 3.1 log₁₀ mean tissue culture infectious doses/bird). The vaccine conferred 100% clinical protection and a significant decrease in oral and cloacal virus shedding from 1995 H5/HP virus challenged birds when compared to the sham controls at all tested doses. Virus shedding titers from vaccinated 2010 H5/LP virus challenged birds significantly decreased compared to sham birds especially at earlier time points. Our results confirm the efficacy of the new rFPV-H5/2016 against antigenic drift of LPAI virus in Mexico and suggest that this vaccine would be a good candidate, likely as a primer in a prime-boost vaccination program.

Domestic ducks play a major role in the maintenance and spread of H5N8 highly pathogenic avian influenza viruses in South Korea

The H5N8 highly pathogenic avian influenza viruses (HPAIVs) belonging to clade 2.3.4.4 spread from Eastern China to Korea in 2014 and caused outbreaks in domestic poultry until 2016. To understand how H5N8 HPAIVs spread at host species level in Korea during 2014-2016, a Bayesian phylogenetic analysis was used for ancestral state reconstruction and estimation of the host transition dynamics between wild waterfowl, domestic ducks and chickens. Our data support that H5N8 HPAIV most likely transmitted from wild waterfowl to domestic ducks, and then maintained in domestic ducks followed by dispersal of HPAIV from domestic ducks to chickens, suggesting domestic duck population plays a central role in the maintenance, amplification and spread of wild HPAIV to terrestrial poultry in Korea.

Pathobiology and innate immune responses of gallinaceous poultry to clade 2.3.4.4A H5Nx highly pathogenic avian influenza virus infection

In the 2014-2015 Eurasian lineage clade 2.3.4.4A H5 highly pathogenic avian influenza (HPAI) outbreak in the U.S., backyard flocks with minor gallinaceous poultry and large commercial poultry (chickens and turkeys) operations were affected. The pathogenesis of the first H5N8 and reassortant H5N2 clade 2.3.4.4A HPAI U.S. isolates was investigated in six gallinaceous species: chickens, Japanese quail, Bobwhite quail, Pearl guinea fowl, Chukar partridges, and Ring-necked pheasants. Both viruses caused 80-100% mortality in all species, except for H5N2 virus that caused 60% mortality in chickens. The surviving challenged birds remained uninfected based on lack of clinical disease and lack of seroconversion. Among the infected birds, chickens and Japanese quail in early clinical stages (asymptomatic and listless) lacked histopathologic findings. In contrast, birds of all species in later clinical stages (moribund and dead) had histopathologic lesions and systemic virus replication consistent with HPAI virus infection in gallinaceous poultry. These birds had widespread multifocal areas of necrosis, sometimes with heterophilic or lymphoplasmacytic inflammatory infiltrate, and viral antigen in parenchymal cells of most tissues. In general, lesions and antigen distribution were similar regardless of virus and species. However, endotheliotropism was the most striking difference among species, with only Pearl guinea fowl showing widespread replication of both viruses in endothelial cells of most tissues. The expression of IFN-γ and IL-10 in Japanese quail, and IL-6 in chickens, were up-regulated in later clinical stages compared to asymptomatic birds.

Rapid evolution of Mexican H7N3 highly pathogenic avian influenza viruses in poultry

Highly pathogenic avian influenza (HPAI) virus subtype H7N3 has been circulating in poultry in Mexico since 2012 and vaccination has been used to control the disease. In this study, eight Mexican H7N3 HPAI viruses from 2015–2017 were isolated and fully sequenced. No evidence of reassortment was detected with other avian influenza (AI) viruses, but phylogenetic analyses show divergence of all eight gene segments into three genetic clusters by 2015, with 94.94 to 98.78 percent nucleotide homology of the HA genes when compared to the index virus from 2012. The HA protein of viruses from each cluster showed a different number of basic amino acids (n = 5–7) in the cleavage site, and six different patterns at the predicted N-glycosylation sites. Comparison of the sequences of the Mexican lineage H7N3 HPAI viruses and American ancestral wild bird AI viruses to characterize the virus evolutionary dynamics showed that the nucleotide substitution rates in PB2, PB1, PA, HA, NP, and NS genes greatly increased once the virus was introduced into poultry. The global nonsynonymous and synonymous ratios imply strong purifying selection driving the evolution of the virus. Forty-nine positively selected sites out of 171 nonsynonymous mutations were identified in the Mexican H7N3 HPAI viruses, including 7 amino acid changes observed in higher proportion in North American poultry origin AI viruses isolates than in wild bird-origin viruses. Continuous monitoring and molecular characterization of the H7N3 HPAI virus is important for better understanding of the virus evolutionary dynamics and further improving control measures including vaccination.

Transmission Dynamics of Highly Pathogenic Avian Influenza Virus A(H5Nx) Clade 2.3.4.4, North America, 2014-2015

Eurasia highly pathogenic avian influenza virus (HPAIV) H5 clade 2.3.4.4 emerged in North America at the end of 2014 and caused outbreaks affecting >50 million poultry in the United States before eradication in June 2015. We investigated the underlying ecologic and epidemiologic processes associated with this viral spread by performing a comparative genomic study using 268 full-length genome sequences and data from outbreak investigations. Reassortant HPAIV H5N2 circulated in wild birds along the Pacific flyway before several spillover events transmitting the virus to poultry farms. Our analysis suggests that >3 separate introductions of HPAIV H5N2 into Midwest states occurred during March–June 2015; transmission to Midwest poultry farms from Pacific wild birds occurred ≈1.7–2.4 months before detection. Once established in poultry, the virus rapidly spread between turkey and chicken farms in neighboring states. Enhanced biosecurity is required to prevent the introduction and dissemination of HPAIV across the poultry industry.

New Reassortant Clade 2.3.4.4b Avian Influenza A(H5N6) Virus in Wild Birds, South Korea, 2017-18

We isolated new reassortant avian influenza A(H5N6) viruses from feces of wild waterfowl in South Korea during 2017–18. Phylogenetic analysis suggested that reassortment occurred between clade 2.3.4.4b H5N8 and Eurasian low pathogenicity avian influenza viruses circulating in wild birds. Dissemination to South Korea during the 2017 fall migratory season followed.

Intercontinental spread of Asian-origin H7 avian influenza viruses by captive bird trade in 1990's

Wild bird migration and illegal trade of infected poultry, eggs, and poultry products have been associated with the spread of avian influenza viruses (AIV). During 1992-1996, H7N1 and H7N8 low pathogenic AIV (LPAIV) were identified from captive wild birds; such as Pekin robin (Leiothrix lutea), magpie robin (Copsychus saularis), flycatcher sp. (genus Empidonax), a species of softbill and parakeet, sun conure (Aratinga solstitialis), painted conure (Pyrrhura picta), fairy bluebird (Irena puella), and common iora (Aegithina tiphia), kept in aviaries or quarantine stations in England, The Netherlands, Singapore and the United States (U.S.). In this study, we sequenced these H7 viruses isolated from quarantine facilities and aviaries using next-generation sequencing and conducted a comparative phylogenetic analysis of complete genome sequences to elucidate spread patterns. The complete genome sequencing and phylogenetic analysis suggested that H7 viruses originated from a common source, even though they were obtained from birds in distant geographical regions. All H7N1 and H7N8 viruses were LPAIV, except a H7N1 highly pathogenic AIV (HPAIV), A/Pekin robin/California/30412/1994(H7N1) virus. Our results support the continued need for regulation of the captive wild bird trade to reduce the risk of introduction and dissemination of both LPAIV and HPAIV throughout the world.

Reassortant Clade 2.3.4.4 of Highly Pathogenic Avian Influenza A(H5N6) Virus, Taiwan, 2017

A highly pathogenic avian influenza A(H5N6) virus of clade 2.3.4.4 was detected in a domestic duck found dead in Taiwan during February 2017. The endemic situation and continued evolution of various reassortant highly pathogenic avian influenza viruses in Taiwan warrant concern about further reassortment and a fifth wave of intercontinental spread.

A computationally designed H5 antigen shows immunological breadth of coverage and protects against drifting avian strains

Since the first identification of the H5N1 Goose/Guangdong lineage in 1996, this highly pathogenic avian influenza virus has spread worldwide, becoming endemic in domestic poultry. Sporadic transmission to humans has raised concerns of a potential pandemic and underscores the need for a broad cross-protective influenza vaccine. Here, we tested our previously described methodology, termed Computationally Optimized Broadly Reactive Antigen (COBRA), to generate a novel hemagglutinin (HA) gene, termed COBRA-2, that was based on H5 HA sequences from 2005 to 2006. The COBRA-2 HA virus-like particle (VLP) vaccines were used to vaccinate chickens and the immune responses were compared to responses elicited by VLP's expressing HA from A/whooper swan/Mongolia/244/2005 (WS/05), a representative 2005 vaccine virus from clade 2.2. To support this evaluation a hemagglutination inhibition (HAI) breadth panel was developed consisting of phylogenetically and antigenically diverse H5 strains in circulation from 2005 to 2006, as well as recent drift variants (2008 - 2014). We found that the COBRA-2 VLP vaccines elicited robust HAI titers against this entire breadth panel, whereas the VLP vaccine based upon the recommended WS/05 HA only elicited HAI responses against a subset of strains. Furthermore, while all vaccines protected chickens against challenge with the WS/05 virus, only the human COBRA-2 VLP vaccinated birds were protected (80%) against a recent drifted clade 2.3.2.1B, A/duck/Vietnam/NCVD-672/2011 (VN/11) virus. This is the first report to demonstrate seroprotective antibody responses against genetically diverse clades and sub-clades of H5 viruses and protective efficacy against a recent drifted variant using a globular head based design strategy.

Maternal antibody inhibition of recombinant Newcastle disease virus vectored vaccine in a primary or booster avian influenza vaccination program of broiler chickens

Maternally-derived antibodies (MDA) provide early protection from disease, but may interfere with active immunity in young chicks. In highly pathogenic avian influenza virus (HPAIV)-enzootic countries, broiler chickens typically have MDA to Newcastle disease virus (NDV) and H5 HPAIV, and their impact on active immunity from recombinant vectored vaccines is unclear. We assessed the effectiveness of a spray-applied recombinant NDV vaccine with H5 AIV insert (rNDV-H5) and a recombinant turkey herpesvirus (HVT) vaccine with H5 AIV insert (rHVT-H5) in commercial broilers with MDA to NDV alone (MDA:AIV^-NDV⁺) or to NDV plus AIV (MDA:AIV⁺NDV⁺) to provide protection against homologous HPAIV challenge. In Experiment 1, chicks were spray-vaccinated with rNDV-H5 at 3 weeks (3w) and challenged at 5 weeks (5w). All sham-vaccinated progeny lacked AIV antibodies and died following challenge. In rNDV-H5 vaccine groups, AIV and NDV MDA had completely declined to non-detectable levels by vaccination, enabling rNDV-H5 spray vaccine to elicit a protective AIV antibody response by 5w, with 70-78% survival and significant reduction of virus shedding compared to shams. In Experiment 2, progeny were vaccinated with rHVT-H5 and rNDV-H5 at 1 day (1d) or 3w and challenged at 5w. All sham-vaccinated progeny lacked AIV antibodies and died following challenge. In rHVT-H5(1d) vaccine groups, irrespective of rNDV-H5(3w) boost, AIV antibodies reached protective levels pre-challenge, as all progeny survived and virus shedding significantly decreased compared to shams. In contrast, rNDV-H5-vaccinated progeny had AIV and/or NDV MDA at the time of vaccination (1d and/or 3w) and failed to develop a protective immune response by 5w, resulting in 100% mortality after challenge. Our results demonstrate that MDA to AIV had minimal impact on the effectiveness of rHVT-H5, but MDA to AIV and/or NDV at the time of vaccination can prevent development of protective immunity from a primary or booster rNDV-H5 vaccine.

Pathobiology of Tennessee 2017 H7N9 low and high pathogenicity avian influenza viruses in commercial broiler breeders and specific pathogen free layer chickens

In March 2017, H7N9 highly pathogenic avian influenza (HPAI) virus was detected in 2 broiler breeder farms in the state of Tennessee, USA. Subsequent surveillance detected the low pathogenicity avian influenza (LPAI) virus precursor in multiple broiler breeder farms and backyard poultry in Tennessee and neighboring states. The pathogenesis of the H7N9 LPAI virus was investigated in commercial broiler breeders, the bird type mostly affected in this outbreak. Infectivity, transmissibility, and pathogenesis of the H7N9 HPAI and LPAI viruses were also studied in 4-week-old specific pathogen free (SPF) leghorn chickens. The mean bird infectious doses (BID₅₀) for the LPAI isolate was 5.6 log₁₀ mean egg infectious dose (EID₅₀) for broiler breeders and 4.3 log₁₀ EID₅₀ for SPF layer chickens, and no transmission to contact-exposed birds was observed. In both bird types, virus shedding was almost exclusively from the oropharyngeal route. These findings suggest sub-optimal adaptation for sustained transmission with the H7N9 LPAI isolate, indicating that factors other than the birds genetic background may explain the epidemiology of the outbreak. The BID₅₀ for the HPAI isolate in SPF layer chickens was more than 2 logs lower (<2 log₁₀ EID₅₀) than the LPAI isolate. Also, the HPAI virus was shed by both the oropharyngeal and cloacal routes and transmitted to contacts. Greater susceptibility and easier transmission of the H7N9 HPAI virus are features of the HP phenotype that could favor the spread of HPAI over LPAI viruses during outbreaks.

Mitigation strategies to reduce the generation and transmission of airborne highly pathogenic avian influenza virus particles during processing of infected poultry

Airborne transmission of H5N1 highly pathogenic avian influenza (HPAI) viruses has occurred among poultry and from poultry to humans during home or live-poultry market slaughter of infected poultry, and such transmission has been experimentally reproduced. In this study, we investigated simple, practical changes in the processing of H5N1 virus-infected chickens to reduce infectious airborne particles and their transmission. Our findings suggest that containing the birds during the killing and bleeding first step by using a disposable plastic bag, a commonly available cooking pot widely used in Egypt (halla), or a bucket significantly reduces generation of infectious airborne particles and transmission to ferrets. Similarly, lack of infectious airborne particles was observed when processing vaccinated chickens that had been challenged with HPAI virus. Moreover, the use of a mechanical defeatherer significantly increased total number of particles in the air compared to manual defeathering. This study confirms that simple changes in poultry processing can efficiently mitigate generation of infectious airborne particles and their transmission to humans.

Experimental infection of H5N1 and H5N8 highly pathogenic avian influenza viruses in Northern Pintail (Anas acuta)

The wide geographic spread of Eurasian Goose/Guangdong lineage highly pathogenic avian influenza (HPAI) clade 2.3.4.4 viruses by wild birds is of great concern. In December 2014, an H5N8 HPAI clade 2.3.4.4 Group A (2.3.4.4A) virus was introduced to North America. Long-distance migratory wild aquatic birds between East Asia and North America, such as Northern Pintail (Anas acuta), were strongly suspected of being a source of intercontinental transmission. In this study, we evaluated the pathogenicity, infectivity and transmissibility of an H5N8 HPAI clade 2.3.4.4A virus in Northern Pintails and compared the results to that of an H5N1 HPAI clade 2.3.2.1 virus. All of Northern Pintails infected with either H5N1 or H5N8 virus lacked clinical signs and mortality, but the H5N8 clade 2.3.4.4 virus was more efficient at replicating within and transmitting between Northern Pintails than the H5N1 clade 2.3.2.1 virus. The H5N8-infected birds shed high titre of viruses from oropharynx and cloaca, which in the field supported virus transmission and spread. This study highlights the role of wild waterfowl in the intercontinental spread of some HPAI viruses. Migratory aquatic birds should be carefully monitored for the early detection of H5 clade 2.3.4.4 and other HPAI viruses.

Detection of reassortant H5N6 clade 2.3.4.4 highly pathogenic avian influenza virus in a black-faced spoonbill (Platalea minor) found dead, Taiwan, 2017

A H5N6 highly pathogenic avian influenza virus (HPAIV) was detected in a black-faced spoonbill (Platalea minor) found dead in Taiwan during December 2017. Genome sequencing and phylogenetic analyses suggest the hemagglutinin gene belongs to H5 clade 2.3.4.4 Group B. All genes except neuraminidase gene shared high levels of nucleotide identity with H5N8 HPAIV identified from Europe during 2016-2017. Genetically similar H5N6 HPAIV was also identified from Japan during November 2017. Enhanced surveillance is required in this region.

Evolution, global spread, and pathogenicity of highly pathogenic avian influenza H5Nx clade 2.3.4.4

Novel subtypes of Asian-origin (Goose/Guangdong lineage) H5 highly pathogenic avian influenza (HPAI) viruses belonging to clade 2.3.4, such as H5N2, H5N5, H5N6, and H5N8, have been identified in China since 2008 and have since evolved into four genetically distinct clade 2.3.4.4 groups (A–D). Since 2014, HPAI clade 2.3.4.4 viruses have spread rapidly via migratory wild aquatic birds and have evolved through reassortment with prevailing local low pathogenicity avian influenza viruses. Group A H5N8 viruses and its reassortant viruses caused outbreaks in wide geographic regions (Asia, Europe, and North America) during 2014–2015. Novel reassortant Group B H5N8 viruses caused outbreaks in Asia, Europe, and Africa during 2016–2017. Novel reassortant Group C H5N6 viruses caused outbreaks in Korea and Japan during the 2016–2017 winter season. Group D H5N6 viruses caused outbreaks in China and Vietnam. A wide range of avian species, including wild and domestic waterfowl, domestic poultry, and even zoo birds, seem to be permissive for infection by and/or transmission of clade 2.3.4.4 HPAI viruses. Further, compared to previous H5N1 HPAI viruses, these reassortant viruses show altered pathogenicity in birds. In this review, we discuss the evolution, global spread, and pathogenicity of H5 clade 2.3.4.4 HPAI viruses.

Airborne Transmission of Highly Pathogenic Influenza Virus during Processing of Infected Poultry

Exposure to infected poultry is a suspected cause of avian influenza (H5N1) virus infections in humans. We detected infectious droplets and aerosols during laboratory-simulated processing of asymptomatic chickens infected with human- (clades 1 and 2.2.1) and avian- (clades 1.1, 2.2, and 2.1) origin H5N1 viruses. We detected fewer airborne infectious particles in simulated processing of infected ducks. Influenza virus–naive chickens and ferrets exposed to the air space in which virus-infected chickens were processed became infected and died, suggesting that the slaughter of infected chickens is an efficient source of airborne virus that can infect birds and mammals. We did not detect consistent infections in ducks and ferrets exposed to the air space in which virus-infected ducks were processed. Our results support the hypothesis that airborne transmission of HPAI viruses can occur among poultry and from poultry to humans during home or live-poultry market slaughter of infected poultry.

Reoccurrence of Avian Influenza A(H5N2) Virus Clade 2.3.4.4 in Wild Birds, Alaska, USA, 2016

We report reoccurrence of highly pathogenic avian influenza A(H5N2) virus clade 2.3.4.4 in a wild mallard in Alaska, USA, in August 2016. Identification of this virus in a migratory species confirms low-frequency persistence in North America and the potential for re-dissemination of the virus during the 2016 fall migration.

Lessons learned from research and surveillance directed at highly pathogenic influenza A viruses in wild birds inhabiting North America

Following detections of highly pathogenic (HP) influenza A viruses (IAVs) in wild birds inhabiting East Asia after the turn of the millennium, the intensity of sampling of wild birds for IAVs increased throughout much of North America. The objectives for many research and surveillance efforts were directed towards detecting Eurasian origin HP IAVs and understanding the potential of such viruses to be maintained and dispersed by wild birds. In this review, we highlight five important lessons learned from research and surveillance directed at HP IAVs in wild birds inhabiting North America: (1) Wild birds may disperse IAVs between North America and adjacent regions via migration, (2) HP IAVs can be introduced to wild birds in North America, (3) HP IAVs may cross the wild bird-poultry interface in North America, (4) The probability of encountering and detecting a specific virus may be low, and (5) Population immunity of wild birds may influence HP IAV outbreaks in North America. We review empirical support derived from research and surveillance efforts for each lesson learned and, furthermore, identify implications for future surveillance efforts, biosecurity, and population health. We conclude our review by identifying five additional areas in which we think future mechanistic research relative to IAVs in wild birds in North America are likely to lead to other important lessons learned in the years ahead.

Highly Pathogenic Avian Influenza Viruses and Generation of Novel Reassortants, United States, 2014-2015

Asian highly pathogenic avian influenza A(H5N8) viruses spread into North America in 2014 during autumn bird migration. Complete genome sequencing and phylogenetic analysis of 32 H5 viruses identified novel H5N1, H5N2, and H5N8 viruses that emerged in late 2014 through reassortment with North American low-pathogenicity avian influenza viruses.

Highly Pathogenic Avian Influenza A(H7N9) Virus, Tennessee, USA, March 2017

In March 2017, highly pathogenic avian influenza A(H7N9) was detected at 2 poultry farms in Tennessee, USA. Surveillance data and genetic analyses indicated multiple introductions of low pathogenicity avian influenza virus before mutation to high pathogenicity and interfarm transmission. Poultry surveillance should continue because low pathogenicity viruses circulate and spill over into commercial poultry.

Infection with Some Infectious Bursal Disease Virus Pathotypes Produces Virus in Chicken Muscle Tissue and the Role of Humoral Immunity as a Mitigation Strategy

Infectious bursal disease virus (IBDV) causes important economic losses and negatively affects global trade in poultry and poultry products. This study determined the presence of IBDV in primary lymphoid tissues and muscle tissue of infected broilers and the role of vaccination as a mitigation strategy. In the first study, specific-pathogen-free (SPF) broiler chickens were challenged with STC (classical [cIBDV]), Indiana (variant [varIBDV]), rA (very virulent [vvIBDV]), or Ohio (serotype 2, avirulent) IBDV. Infection was confirmed in all groups, but only the cIBDV group experienced morbidity or mortality. Virus was only isolated in low titers from a few breast and/or thigh muscle tissue samples from cIBDV and vvIBDV-infected chickens. For the second study, SPF broilers from three different treatment groups were challenged with IBDV viruses that currently circulate in the United States, varIBDV or vvIBDV: 1) maternal antibody-positive (MAb+), vaccinated with recombinant HVT-IBDV vaccine (Vaxxitek^®, Merial; MAb+/Vax); 2) MAb+, not-vaccinated (MAb+/Unvax); and 3) maternal antibody-negative, not-vaccinated chickens (MAb-/Unvax). MAb+/Vax and MAb+/Unvax chickens had significantly lower virus titers in primary lymphoid tissues compared to MAb-/Unvax chickens. No virus was detected in muscle tissues from any of the groups challenged with varIBDV, confirming the results of the first experiment. Only 1 of 36 (MAb+/Vax) and 2 of 36 (MAb+/Unvax) muscle samples were positive at minimal amounts (10^1.97 EID₅₀/ml) in vvIBDV challenge, compared to the 9 of 36 muscle samples that were positive in the MAb-/Unvax group. This study indicates that only cIBDV and vvIBDV strains can be found in muscle at low titers of SPF meat chickens and that the breeder vaccination with MAb transfer to progeny with or without accompanying progeny vaccination, as practiced in the United States, was an effective mitigation strategy for vvIBDV-challenged birds.