Hantavirus Pulmonary Syndrome: Pathogenesis of an Emerging Infectious Disease

A recent outbreak of a severe pulmonary disease in the southwestern United States was etiologically linked to a previously unrecognized bantavirus. The virus has been isolated from its majorreservoir, the deer mouse, Peromyscus maniculatus,and recently named Sin Nombre virus. Clinically, the disease has become known as the bantavirus pulmonary syndrome (HPS). Since May 1993, 44 fatal cases of HPS have been identified through clinicopathological review and immunobistochemical(IHC) testing of tissues from 273 patients who died of an unexplained noncardiogenic pulmonary edema. In 158 cases for which suitable specimens were available, serologicaltesting and/or reverse transcription-polymerase chain reaction (RT-PCR) amplification of extracted RNA was also performed. IHC, serological, and PCR results were concordant for virtually all HPS and non-HPS patients when more than one assay was performed. The prodromal ilness of HPS is similar to that of many other viral diseases. Consistent bematological features include thrombocytopenia, bemoconcentration, neutropbilic leukocytosis with a left shift, and reactivel lymphocytes. Pulmonary bistopatbological features were similar in most of the fatal HPS cases (40/44) and consisted of an interstitial pneumonitis with a variable mononuclear cell infiltrate, edema, and focal byaline membranes. In four cases, bowever, pulmonary features were significantly different and included diffuse alveolar damage and variable degrees of severe air space disorganization. IHC analysis showed widespread presence of bantaviral antigens in endothelial cells of the microvasculature, particularly in the lung. Hantaviral antigens were also observed within follicular dendritic cells, macrophages, and lymphocytes. Hantaviral inclusions were observed in endothelial cells of lungs by thinsection electron microscopy, and their identity was verified by immunogold labeling. Virus-like particles were seen in pulmonary endothelial cells and macropbages. HPS is a newly recognized, often fatal disease, with a spectrum of microscopic morphological changes, which may be an important cause of severe and fatal illness presenting as adult respiratory distress syndrome.