H1N1 virus is sometimes mentioned in the news with reference to which one of the following diseases?

The correct answer is D, Swine flu. H1N1 is a subtype of influenza A virus, named by its two surface proteins: haemagglutinin (H1) and neuraminidase (N1). The 2009 pandemic strain was a reassortant carrying genes from swine, avian and human influenza viruses, which is why it was called swine flu.

• A) AIDS is wrong. It is caused by HIV, a retrovirus, not an influenza virus.
• B) Bird flu is wrong. Avian influenza is mainly associated with subtypes such as H5N1 and H7N9. H1N1 is not the bird flu subtype, though aspirants often confuse the two because both are influenza.
• C) Dengue is wrong. It is caused by a flavivirus spread by Aedes mosquitoes.

The core concept is influenza subtyping and zoonotic spillover. Pandemic preparedness and the One Health approach, which links human, animal and environmental health, are a useful Mains angle here. H1N1 now circulates as a seasonal influenza strain alongside other subtypes.

Trap: Seeing the letter H and assuming bird flu. Subtype names tell you the surface protein, not the host animal.