PATHOGENICITY OF AVIAN INFLUENZA VIRUSES IN POULTRY

Authors: Swayne, David; Pantin Jackwood, Mary

Submitted to: OIE/FAO International Scientific Conference of Avian Influenza
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2005
Publication Date: 4/7/2005
Citation: Swayne, D.E., Pantin Jackwood, M.J. 2005. Pathogenicity of avian influenza viruses in poultry [abstract]. In: OIE/FAO International Scientific Conference on Avian Influenza, April 7-8, 2005. p.19.

Interpretive Summary:

Technical Abstract: Historically, the pathogenicity of avian influenza (AI) viruses has been defined by experimental studies in the major poultry species, chickens. All AI viruses are classified into two broad categories, low pathogenicity (LP) and high pathogenicity (HP), but pathobiological changes vary by virus strain and host species within each of the categories. Typically, AI viruses that are HP for chicken produce a similar severe, systemic disease in other galliforme birds, but usually produce mild disease or no infection in ducks. The 1959-1984 H5 HPAI viruses produced longer mean death times in chickens than the newer H5 and the H7 HPAI viruses, suggesting a shift to increased virulence for chickens. All the Asian H5N1 AI viruses are HP for chickens with large quantities of virus being shed from the oropharynx and slightly lesser amount from the cloaca. The Asia H5N1 AI viruses have changed from producing inconsistent infection in ducks to some strains being HP (HK 2002 viruses) and resulting in excretion of large virus quantities from respiratory, and to lesser extent, intestinal tracts. However, the quantities are still 2log10 less than seen in chickens. Across all bird species, the ability to produce severe disease and death is associated with the virus replicating to high titers in the host. In galliforme birds, the Asian H5N1 HPAI viruses replicate in vascular endothelial cells and/or multiple parenchymal organs and the brain. This leads to production of widespread necrosis and inflammation in multiple organs. With geese, emu, house finches and budgerigars, the virus infects neurons and glial cells producing neurological signs and mortality rates ranging from 0-75%. The heart and pancreas are also affected. In domestic ducks, the lesions have been mild and usually only present in the respiratory tract, but internal organs and the brain have been affected if using the 2002 HK H5N1 viruses. With 2003-2004 Asian H5N1 AI viruses, lethality in ducks has been age dependent.