Virus Structure and Classification (2B) Practice Test

In a surveillance study, an unknown respiratory virus (Virus X) was isolated from nasopharyngeal swabs and purified. Treatment of intact virions with 0.1% Triton X-100 reduced infectivity to <1% of baseline, while treatment with RNase A had no effect unless detergent was added first. Viral replication in cultured cells was inhibited by a compound that blocks RNA-dependent RNA polymerase (RdRP). Electron microscopy showed pleomorphic particles with surface projections.

Which classification best fits Virus X based on these observations?

A respiratory isolate (Virus X) was tested in cultured epithelial cells. Infectivity decreased by 3.5 log10 after 10 minutes of exposure to 70% ethanol, but was unchanged after incubation with RNase A (with intact virions present). When purified virions were treated with a nonionic detergent before RNase A exposure, the viral genome became RNase-sensitive. In a separate assay, viral replication was not inhibited by a DNA polymerase inhibitor that blocks host nuclear DNA synthesis. Based on these observations, which classification best fits Virus X?