Respiratory viruses with club-shaped peplomers: Which agent classically has surface spikes (peplomers) that appear club-shaped and commonly infects the human respiratory tract?

Introduction / Context:
“Peplomers” are the glycoprotein spikes seen on the surface of enveloped viruses. Coronaviruses are named for their corona-like appearance due to prominent, club-shaped spike (S) proteins, and they commonly infect the upper and lower respiratory tract.

Given Data / Assumptions:

• We are comparing surface morphology across common viruses.
• Target organ system: respiratory tract.
• Select the agent with club-shaped peplomers.

Concept / Approach:
Coronaviruses are enveloped and have large, club-shaped spikes responsible for receptor binding and membrane fusion. Astroviruses and noroviruses are non-enveloped enteric viruses lacking peplomer spikes; their infections primarily involve the gastrointestinal tract.

Step-by-Step Solution:
Identify peplomers → requires an enveloped virus. Coronaviruses: enveloped with club-shaped S glycoprotein; respiratory tropism common. Astrovirus and norovirus → non-enveloped, GI pathogens, no peplomers. Select Coronavirus.

Verification / Alternative check:
Electron micrographs show a “crown” of clubs on coronaviruses; clinical correlation with colds, SARS-like illnesses, and other respiratory syndromes supports the choice.

Why Other Options Are Wrong:
Astrovirus and norovirus lack envelopes and do not have club-shaped spikes; “All of these” is therefore incorrect; adenovirus has fiber projections but is non-enveloped and not club-peplomer based.

Common Pitfalls:
Assuming all surface projections are “peplomers.” Only enveloped viruses display peplomer spikes; non-enveloped viruses have capsid features instead.

Final Answer:
Coronavirus.