Environmental stability: Which of the following viruses is relatively thermostable (i.e., can better withstand heat compared with many other enveloped respiratory viruses)?

Introduction / Context:
Virion stability in the environment varies with structure and composition. Enveloped viruses are generally more labile to heat, desiccation, and detergents, whereas many nonenveloped, icosahedral RNA viruses are more resistant. Identifying thermostable viruses informs disinfection practices and food/water safety.

Given Data / Assumptions:

• Hepatitis A virus (HAV) is a nonenveloped, positive-sense RNA picornavirus.
• Influenza virus, HIV, and rubella virus are enveloped and relatively heat-labile.
• “Relatively thermostable” implies comparative robustness, not absolute indestructibility.

Concept / Approach:
The presence or absence of a lipid envelope is a key determinant of environmental stability. Nonenveloped viruses like HAV possess sturdy capsids that resist temperature and pH changes better than lipid-enveloped viruses. HAV’s stability underlies transmission via the fecal–oral route and the need for adequate heating and chlorination in food and water handling.

Step-by-Step Solution:

Verification / Alternative check:
Public health guidelines emphasize heating shellfish and proper sanitation to inactivate HAV due to its resilience compared with enveloped respiratory viruses.

Why Other Options Are Wrong:

• Influenza virus: enveloped orthomyxovirus; heat and detergent sensitive.
• Rubella virus: enveloped togavirus; environment-labile.
• Human immunodeficiency virus: enveloped retrovirus; readily inactivated by heat and disinfectants.

Common Pitfalls:
Assuming medical severity correlates with environmental stability; stability is a structural property, not a measure of virulence.

Final Answer:
Hepatitis A virus