Fig 3.

Serially passaging Sin Nombre virus results in increased viral replication in hamster lungs without histological changes associated with HPS. Histological analysis was carried out on lung samples from hamsters infected with passaged Sin Nombre virus and compared to time-matched samples from Andes virus-infected animals. In the initial passage (p1) of Sin Nombre virus, nucleoprotein antigen and RNA were undetectable by immunohistochemistry and in situ hybridization. However, by p5 and continuing through p20, viral antigen and RNA were readily detectable in pulmonary endothelial cells from hamsters infected with the passaged virus, with a distribution and intensity similar to that observed in Andes-infected hamsters. Despite increased replication, no histological lesions were noted in the lungs of hamsters infected with the passaged virus. By comparison, time-matched samples collected from Andes-infected hamsters demonstrated perivascular edema, which ultimately leads to diffuse pulmonary edema and death.