Pathogenesis and pathobiology of avian influenza virus infection in birds

Authors: Pantin Jackwood, Mary; Swayne, David

Submitted to: OIE Scientific and Technical Review
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2009
Publication Date: 7/1/2009
Citation: Pantin Jackwood, M.J., Swayne, D.E. 2009. Pathogenesis and pathobiology of avian influenza virus infection in birds. OIE Scientific and Technical Review. 28(1):113-136.

Interpretive Summary: Avian Influenza (AI) viruses vary in their ability to grow, cause disease and death in different bird species. AI viruses can cause mild disease (low pathogenicity (LP)) or be of the deadly form (high pathogenicity (HP)) in chickens and related terrestrial birds. Both LPAI and HPAI viruses either do not grow or cause only mild disease in domestic ducks and wild birds. However, the H5N1 HPAI viruses have evolved over the past decade with the unique capacity to grow and cause disease in domestic ducks and some wild birds including severe disease, similar to that produced in chickens. Song birds and pigeons are difficult to infect and are unlikely to harbor the H5N1 HPAI virus, but some wild ducks and geese can be severely affected and could spread the virus over intermediate distances.

Technical Abstract: Avian Influenza (AI) viruses vary in their ability to produce infection, disease and death in different bird species. Based on the pathobiological features in chickens, AI viruses are categorized as, low (LP) and high pathogenicity (HP). Typically, LPAI (low pathogenicity avian influenza) viruses cause asymptomatic infections in wild aquatic birds, but when introduced into domesticated poultry, infections may be asymptomatic or produce clinical signs and lesions reflecting pathophysiological damage to the respiratory, digestive and reproductive systems. The HPAI (high pathogenicity avian influenza) viruses have primarily been seen in gallinaceous poultry, producing high morbidity and mortality rates, and systemic disease with necrosis and inflammation in multiple visceral organs, nervous and cardiovascular systems, and the integument. Although HPAI viruses have rarely infected domestic waterfowl or wild birds, the Eurasian-African H5N1 HPAI viruses have evolved over the past decade with the unique capacity to infect and cause disease in domestic ducks and wild birds producing a range of syndromes including asymptomatic respiratory and digestive tract infections; systemic disease limited to 2-3 critical organs usually the brain, heart and pancreas; and severe disseminated infection and death a seen in gallinaceous poultry. Although experimental studies using intranasal inoculation have produced infection in a variety of wild bird species, the inefficiency of the contact transmission in some of them, for example passerines and columbiforms, suggests they are unlikely to be a reservoir for the viruses, while some others like wild anseriforms, can be severely affected and could serve as a dissemination host over intermediate distances.