[Histopathologic study of avian influenza H5N1 infection in humans]

To identify histopathologic changes of major organs and to correlate clinical symptoms in patients infected by avian influenza H5N1.

Autopsy study was performed in two patients died of avian influenza HSN1 infection, following conventional protocols and strict safety procedures. Tissue samples from all major organs of two cases and lung samples of one case were collected and fixed in 4% formaldehyde. Histopathologic changes were evaluated by light microscope.

Diffuse alveolar damage (DAD) of the lung was seen in both cases. Lesions at various stages of development were seen involving different areas of the lung. At the early stages, the lungs exhibited exudative changes, including capillary congestion, necrosis of alveolar epithelial cells, and intra-alveolar edema. Hyaline membranes were prominent and diffusely distributed along alveoli. In the middle-late stages of the disease, the lungs exhibited proliferative and fibrotic changes, including proliferation of pneumocytes and bronchial epithelium, fibrosis of the interstitium and alveolar spaces. Lung biopsy tissue of one case showed DAD and interstitial fibrosis in a background of bronchiectasis. Lymph nodes and spleens showed quantity reduction of lymphocytes and active hemophagocytosis. Other changes in major organs included interstitial carditis in one case and acute renal tubular necrosis in one case. In one case, the brain showed edema with cytoplasmic eosinophilia, loss of structure, axon welling and focal necrosis around ventricle. Multiple foci of trophoblastic necrosis with dystrophic calcification were observed in placenta of one pregnant patient. Acute necrotizing deciduitis was found focally. Sections of fetal lung showed edema and scattered interstitial neutrophils were consistent with acute interstitial pneumonitis.

The respiratory tract is the major target of avian influenza A H5N1 virus infection. The changes of DAD in the lungs resulted in hypoxia, leading to multiple organ failure and death.