ABSTRACT
<p><b>OBJECTIVE</b>To report the postmortem findings of a case of highly pathogenic H5N1 avian influenza virus occurring in human beings.</p><p><b>METHODS</b>Postmortem examination was carried out in a deceased caused by highly pathogenic H5N1 avian influenza virus. Detailed light microscopy of major organs, including heart, lungs, liver, spleen, kidneys and brain, was performed. The lung tissue was further investigated by histochemistry, immunohistochemistry and electron microscopy.</p><p><b>RESULTS</b>Major histopathologic changes in lungs secondary to highly pathogenic H5N1 avian influenza virus included diffuse alveolar damage, hyaline membrane formation and focal hemorrhage. Some of the alveolar spaces contained lightly eosinophilic liquid, lymphocytes, macrophages, plasma cells and small number of neutrophils. Congested capillaries were commonly seen in the alveolar septa which were focally rimmed by hyaline membrane. Immunohistochemical study showed that the lymphocytes were mainly of T lineage and macrophages were also demonstrated.</p><p><b>CONCLUSIONS</b>Highly pathogenic H5N1 avian influenza virus causes pathologic changes mostly in lungs, including diffuse alveolar damage and acute exudative changes (involving mainly T lymphocytes and macrophages). The resulting parenchymal destruction, consolidation, pulmonary edema and hemorrhage eventually lead to respiratory distress and death.</p>