Name a common disease caused by the influenza virus.

The flu, or influenza, is the disease directly caused by the influenza virus itself. Influenza is characterized by sudden onset of fever, chills, body aches, fatigue, cough, sore throat, and runny or stuffy nose. Importantly, influenza can lead to severe complications, especially in vulnerable populations, and is typically more pervasive during the winter months.

While pneumonia is a potential complication that can arise from influenza, it is not the primary disease caused by the influenza virus. Meningitis, an inflammation of the protective membranes covering the brain and spinal cord, is caused by different pathogens and does not have a direct association with the influenza virus. HIV/AIDS is caused by the human immunodeficiency virus and is unrelated to influenza. Thus, identifying the flu as the direct disease caused by the influenza virus is crucial in understanding its impact and the need for vaccination and treatment in affected individuals.