AA amyloidosis in vaccinated growing chickens.

Systemic amyloid-A (AA) amyloidosis in birds occurs most frequently in waterfowl such as Pekin ducks. In chickens, AA amyloidosis is observed as amyloid arthropathy. Outbreaks of systemic amyloidosis in flocks of layers are known to be induced by repeated inflammatory stimulation, such as those resulting from multiple vaccinations with oil-emulsified bacterins. Outbreaks of fatal AA amyloidosis were observed in growing chickens in a large scale poultry farm within 3 weeks of vaccination with multiple co-administered vaccines. This study documents the histopathological changes in tissues from these birds. Amyloid deposits were also observed at a high rate in the tissues of apparently healthy chickens. Vaccination should therefore be considered as a potential risk factor for the development of AA amyloidosis in poultry.