Acid stability among picornaviruses: Which listed viruses are acid-labile (readily inactivated by gastric acid) and therefore typically confined to the upper respiratory tract rather than the gut?

Introduction:
A classic distinguishing feature among picornaviruses is their response to acidic pH. Acid stability correlates with transmission route and tissue tropism. This item tests whether you can identify the acid-labile outlier responsible for common colds.

Given Data / Assumptions:

• Enteroviruses (polio, coxsackie, echo) typically survive gastric acidity.
• Rhinoviruses are associated with the upper respiratory tract.
• We choose the virus group inactivated by stomach acid.

Concept / Approach:
Rhinoviruses are acid-labile and grow best at cooler temperatures of the nasal mucosa, favoring transmission by respiratory secretions and fomites. In contrast, enteroviruses are acid-stable, enabling fecal–oral spread and intestinal replication.

Step-by-Step Solution:
Partition picornaviruses into respiratory (rhinoviruses) and enteric (enteroviruses). Recall the acid sensitivity profile. Select the acid-labile group: rhinoviruses. Exclude enteroviruses that tolerate gastric pH.

Verification / Alternative check:
Laboratory conditions for rhinovirus culture use near-neutral pH and lower temperatures; enteroviruses survive simulated gastric fluid, matching their epidemiology.

Why Other Options Are Wrong:
Echoviruses, Polioviruses, Coxsackieviruses – all are enteroviruses and are characteristically acid-stable.

None – incorrect because rhinoviruses are the well-known acid-labile group.

Common Pitfalls:
Confusing “labile” with “stable”; remember “rhino” for nose/respiratory and acid-labile.

Final Answer:
Rhinoviruses.