Akanbi, OlatundeTeifke, JensEkong, PiusIghodalo, E TOyetunde, I LOgunsan, E AMakinde, A A2019-11-012019-11-012007http://hdl.handle.net/123456789/3339Nigeria experienced an outbreak of Highly Pathogenic Avian Influenza (HPAI) H5N1 virus in both commercial and local poultry populations during January, 2006 as an extension of the global outbreaks. Up till August 2007, a total of 25 States of the 36 States of the Federation and the Federal Capital Territory (Abuja) have been affected by these outbreaks that occurred in about 200 premises, causing the death of millions of chickens. In younger birds and local chickens HPAI viruses caused rapid widespread mortality with minimal clinical evidence of disease while manifestation of clinical disease tended to be more overt with older flocks. Birds with HPAI typically presented with nonspecific signs of severe progressive depression, anorexia, decreased activity, huddling, and ruffled feathers. Somnolence, prostration, conjunctival pallor, catarrhal rhinitis, swollen and cyanotic combs and wattles sometimes congested and haemorrhagic, greenish-yellow diarrhoea, during high morbidity with mortalities up to 100% were observed in affected commercial and local flocks. Following confirmatory diagnosis by virus isolation, investigation of the organ predilections of the virus in formalin-fixed, paraffin-embedded (FFPE) tissues using histopathology and immunohistochemistry were carried out. Histologic lesions were observed in multiple organs and were characterized by hemorrhage, necrosis, mild inflammatory exudate, or a combination of these. In particular, the lung, heart, brain, spleen, pancreas, kidneys, combs and wattles were the most consistently affected tissues, which corroborated with the high predilection of viral antigen detected by immunohistochemistry in these organs. The advantage of immunohistochemistry over other diagnostic methods in HPAI diagnosis is invaluable in retrospective studies of FFPE tissues. In the near future, work up of cases which had similar lesions which may have been misdiagnosed or ignored due to the non incidence of HPAI in Nigeria prior to that period would be conducted.enEpidemiologyHPAIImmunohistochemistryArticle