{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,1]],"date-time":"2026-05-01T20:40:05Z","timestamp":1777668005731,"version":"3.51.4"},"reference-count":13,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2026,4,28]],"date-time":"2026-04-28T00:00:00Z","timestamp":1777334400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Viruses"],"abstract":"<jats:p>The 2022 highly pathogenic avian influenza (HPAI) outbreak of H5N1 clade 2.3.4.4b was one of the major avian influenza outbreaks, leading to multiple spillover events infecting domestic and wild bird flocks, as well as mammals. The sustained spread was a result of viral circulation in wild birds across migratory flyways in North America. Pennsylvania has a significant poultry population that supports both retail and live bird markets. The state also features migratory bird stopovers on the Atlantic flyway, increasing exposure to HPAI infections. This study investigates clinical presentation and sequence data from H5N1 clade 2.3.4.4b viruses during the 2022 outbreak in Pennsylvania. Eight different H5N1 clade 2.3.4.4b genotypes were detected (A1, B1.1, B1.2, B1.3, B2.2, B3.3, B3.5, and one minor genotype) during the first year. The earliest detection was genotype A1, a fully Eurasian virus, in commercial poultry in April 2022. All other genotypes identified were reassortants of A1 with North American avian influenza gene segments (denoted with \u201cB\u201d). Genotype B3.3 was a rare genotype prior to the initial spillover into the live bird market system, but remained predominant among backyard flocks in Pennsylvania and surrounding states until September 2023. Genotype B3.3 has not been detected in migratory waterfowl since, suggesting the genotype has waned and is no longer in circulation. This study sheds light on the genotype diversity of H5N1 during the 2022 outbreak in Pennsylvania poultry, contributing to the understanding of virus evolution and its potential impacts.<\/jats:p>","DOI":"10.3390\/v18050502","type":"journal-article","created":{"date-parts":[[2026,4,29]],"date-time":"2026-04-29T07:43:51Z","timestamp":1777448631000},"page":"502","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Genotype Diversity of Highly Pathogenic Avian Influenza H5N1 Clade 2.3.4.4b in Pennsylvania Poultry During Disease Outbreak from April 2022 to March 2023"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7780-3026","authenticated-orcid":false,"given":"Deepanker","family":"Tewari","sequence":"first","affiliation":[{"name":"Pennsylvania Veterinary Laboratory, Harrisburg, PA 17110, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5674-6846","authenticated-orcid":false,"given":"Manoj K.","family":"Sekhwal","sequence":"additional","affiliation":[{"name":"Department of Veterinary and Biomedical Sciences, Penn State University, State College, PA 18432, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9904-5799","authenticated-orcid":false,"given":"Chrislyn","family":"Nicholson","sequence":"additional","affiliation":[{"name":"Animal and Plant Health Inspection Service, Harrisburg, PA 17110, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8613-2009","authenticated-orcid":false,"given":"Mary L.","family":"Killian","sequence":"additional","affiliation":[{"name":"National Veterinary Services Laboratories, Ames, IA 50010, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Corey","family":"Zellers","sequence":"additional","affiliation":[{"name":"Pennsylvania Veterinary Laboratory, Harrisburg, PA 17110, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Julia","family":"Livengood","sequence":"additional","affiliation":[{"name":"Pennsylvania Veterinary Laboratory, Harrisburg, PA 17110, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kristina","family":"Lantz","sequence":"additional","affiliation":[{"name":"National Veterinary Services Laboratories, Ames, IA 50010, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mia","family":"Torchetti","sequence":"additional","affiliation":[{"name":"National Veterinary Services Laboratories, Ames, IA 50010, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alex","family":"Hamberg","sequence":"additional","affiliation":[{"name":"Pennsylvania Department of Agriculture, Harrisburg, PA 17110, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,4,28]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"109860","DOI":"10.1016\/j.virol.2023.109860","article-title":"H5N1 highly pathogenic avian influenza clade 2.3.4.4b in wild and domestic birds: Introductions into the United States and reassortments, December 2021\u2013April 2022","volume":"587","author":"Youk","year":"2023","journal-title":"Virology"},{"key":"ref_2","unstructured":"U.S. Department of Agriculture, Animal and Plant Health Inspection Service (2024, September 25). 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Microbes Infect."}],"container-title":["Viruses"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1999-4915\/18\/5\/502\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,29]],"date-time":"2026-04-29T07:48:35Z","timestamp":1777448915000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1999-4915\/18\/5\/502"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,28]]},"references-count":13,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2026,5]]}},"alternative-id":["v18050502"],"URL":"https:\/\/doi.org\/10.3390\/v18050502","relation":{},"ISSN":["1999-4915"],"issn-type":[{"value":"1999-4915","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,28]]}}}