The molecular background of infectivity and pathogenicity of avian influenza (AI) and Newcastle disease (ND) viruses are described, especially the role of proteolytic cleavage in the activation of haemagglutinin and fusion polypeptides of AI and ND virus, respectively, which results in virulence of these viruses. The significance of amino acid sequences of the proteolytic enzyme recognition site, which correlate to virulence and whose determination can replace pathogenicity tests performed in animals is discussed. The inclusion of these results in the official definition of the diseases is explained. The consequences of long-term evolutionary forces on the ecology and the present manifestation of epidemiology are also treated. Special emphasis is laid on the discovery that highly pathogenic avian influenza (HPAI) viruses may emerge in chicken flocks persistently infected by low pathogenic avian influenza (LPAI) viruses, due to the generation and selection of basic amino acids at the proteolytic cleavage site. Events of AI epizootics (in the United States, Mexico and Italy) and an ND outbreak (in Australia) that emerged due to in situ changes of amino acid sequence at the proteolytic cleavage site and an increase of pathogenicity are treated in some details. The proposal for the inclusion of novel scientific results in the definition of AI, put forward by an expert committee is also discussed (5).
|Translated title of the contribution||Avian influenza and Newcastle disease: Pathogenicity, epidemiology and evolution - Comments on the definition of the diseases|
|Number of pages||14|
|Journal||Magyar Allatorvosok Lapja|
|Publication status||Published - Feb 1 2004|
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