Pathology of highly pathogenic avian influenza H5N1 in the chicken Gallus domesticus

Four white leghorn chickens were challenged with Avian Influenza Virus (H5N1) via the ocular and nasal route to mimic the natural route of infection. Clinical Signs included depression, ruffled feathers and death. Gross examination revealed comb cyanosis, cutaneous hemorrhage, and edema of the head. They were in good body and feather condition, and there was no staining around the cloaca. Multifocal hemorrhage within the heart, pneumonia, splenic congestion, pulmonary hemorrhage and pneumonia, mulitfocal pancreatic necrosis, and multifocal to coalescing hemorrhage of the bursa of Fabricious was observed. Histology revealed multi-organ inflammation, hemorrhage and necrosis. Using immunohistochemistry, H5N1 was found in all tissues examined. The birds in this experiment were negative controls as part of a vaccine trial, and showed clinical signs, progression and lesions typical of HPAI in chickens. This paper will outline the clinical signs, pathology and pathogenesis of HPAI H5N1 in the chicken.