Capsid symmetry in human and animal RNA viruses: Which group below correctly lists viruses whose nucleocapsids exhibit helical symmetry?

Introduction / Context:
Viral capsids/nucleocapsids show either icosahedral or helical symmetry in most medically important viruses. Recognizing symmetry helps with identification, pathogenesis, and disinfection strategies.

Given Data / Assumptions:

• Candidate viruses: measles, mumps (Paramyxoviridae), influenza (Orthomyxoviridae), rabies (Rhabdoviridae).
• We ask which have helical nucleocapsids.

Concept / Approach:
Paramyxoviruses (measles, mumps), orthomyxoviruses (influenza), and rhabdoviruses (rabies) are classic examples of enveloped viruses with helical nucleocapsids, though overall virion shapes vary (e.g., bullet-shaped rabies virions).

Step-by-Step Solution:
Recall paramyxoviruses: non-segmented negative-sense RNA with helical nucleocapsid. Recall influenza: segmented negative-sense RNA; ribonucleoprotein complexes are helical. Recall rabies: rhabdovirus with characteristic bullet-shaped helical nucleocapsid. All listed viruses therefore share helical nucleocapsid symmetry.

Verification / Alternative check:
Electron microscopy images and structural studies confirm helical ribonucleoprotein arrangements in these families.

Why Other Options Are Wrong:

• Any single subset omits other correct examples, making them incomplete.

Common Pitfalls:
Confusing external virion shape with nucleocapsid symmetry; symmetry refers to the internal RNA-protein complex, not necessarily to the envelope contour.

Final Answer:
all of these