OBJECTIVETo explore histopathologic and ultrastructural characteristics of human avian influenza (AI) infection and related etiological pathogenesis.

METHODSPostmortem lung and heart samples were collected from the patient who died of avian influenza virus infection on November 29, 2003 in China. Light and electron microscopy, immunohistochemistry and histochemistry were used to investigate the pathological changes.

RESULTSThe main pathological findings included extensive pulmonary consolidation, hemorrhage, pulmonary edema and local hemorrhagic infarct. The lamina of alveoli and bronchioles were abundantly filled with protein-rich fluid, erythrocytes, fibrin and cell debris admixed with many neutrophilis, macrophages, lymphocytes and a few of monokaryon and multinuclear giant cells. Hyaline membranes were formed. Local pulmonary tissues were heavily damaged by hemorrhage and necrosis. Alveolar septum was disintegrated. Mesenchymal edema with a few of macrophages infiltration of heart was found. Electron microscopy showed the avian influenza A virus-like particles (type C and type A) of 80 - 120 nm diameter and envelopes in the cytoplasm of pneumocytes and endothelial cells.

CONCLUSIONSFatal pneumonia associated with highly pathogenic avian influenza A virus (H5N1) infection leads to extensive pulmonary consolidation, edema and marked hemorrhagic necrosis and inflammation. Electron microscopy can identify avian influenza A virus-like particles. The findings may offer an important theoretical basis for clinical diagnosis and treatment.