Influenza is caused by:

Explanation

Influenza is caused specifically by the influenza virus because it belongs to the Orthomyxoviridae family, which has unique properties - it is an enveloped, negative-sense RNA virus with a segmented genome that determines the typical flu symptoms (fever, cough, sore throat, body aches). Other viruses you mentioned - herpesviruses (DNA viruses), variola virus causing smallpox (Poxviridae, DNA virus), and adenoviruses (DNA viruses) - belong to completely different viral families with distinct structures, replication strategies, and disease profiles. They cause illnesses like cold sores, chickenpox/shingles (herpes family), smallpox (variola), or respiratory and eye infections (adenovirus), but not influenza. In short, disease causation is tied to the specific virus family and its biology, so only influenza viruses can cause flu.