title: Characterization of encephalitis in wild birds naturally infected by highly pathogenic avian influenza H5N1.
abstract: During the outbreak of highly pathogenic avian influenza (HPAI) H5N1 in Sweden in 2006, disease and mortality were observed in a number of wild bird species. Encephalitis was one of the most consistent and severe findings in birds submitted for postmortem examination. However, the distribution and severity of the inflammation varied among individuals. This study characterized the encephalitis and the phenotype of the cellular infiltrate in brains of 40 birds of various species naturally infected with HPAI H5N1. Brain sections stained with hematoxylin and eosin and immunostained for influenza A viral antigen were evaluated in parallel to brain sections immunostained with antibodies against T lymphocytes (CD3+), B lymphocytes (CD79a+), macrophages (Lectin RCA-1+), and astrocytes expressing glial fibrillary acidic protein. The virus showed marked neurotropism, and the neuropathology included multifocal to diffuse areas of gliosis and inflammation in the gray matter, neuronal degeneration, neuronophagia, vacuolation of the neuropil, focal necrosis, perivascular cuffing, and meningitis. Broad ranges in severity, neuroanatomical distribution, and type of cellular infiltrate were observed among the different bird species. Since neurotropism is a key feature of HPAI H5N1 infection in birds and other species and because the clinical presentation can vary, the characterization of the inflammation in the brain is important in understanding the pathogenesis of the disease and also has important diagnostic implications for sample selection.
authors.affiliation: Department of Pathology and Wildlife Diseases, National Veterinary Institute (SVA), 751 89, Uppsala, Sweden. Caroline.Brojer@sva.se
authors.forename: Caroline
authors.initials: C
authors.lastname: Bröjer
authors.forename: Erik O
authors.initials: EO
authors.lastname: Agren
authors.forename: Henrik
authors.initials: H
authors.lastname: Uhlhorn
authors.forename: Karin
authors.initials: K
authors.lastname: Bernodt
authors.forename: Désirée S
authors.initials: DS
authors.lastname: Jansson
authors.forename: Dolores
authors.initials: D
authors.lastname: Gavier-Widén
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000378:metabolism; D001715:Bird Diseases / Q000453:epidemiology / Q000473:pathology / Q000821:virology; D001717:Birds; D001921:Brain / Q000276:immunology* / Q000473:pathology / Q000821:virology; D018792:Encephalitis, Viral / Q000453:epidemiology / Q000473:pathology / Q000662:veterinary* / Q000821:virology; D007150:Immunohistochemistry / Q000662:veterinary; D053124:Influenza A Virus, H5N1 Subtype / Q000276:immunology*; D005585:Influenza in Birds / Q000150:complications* / Q000453:epidemiology / Q000821:virology; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013045:Species Specificity; D013548:Sweden / Q000453:epidemiology
chemical_list: D000956:Antigens, Viral