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Influenza is a disease caused by a virus, specifically the influenza virus, which stores its genetic information in the form of ribonucleic acid (RNA). One key characteristic of the influenza virus is its high variability, allowing it to easily evade the human immune defenses. It is believed that the virus originated from water birds, but it has spread across various bird and mammal species. In addition to humans, animals such as poultry, dolphins, and ferrets can also contract the flu. There are many subtypes of influenza viruses, distinguished by the specific forms of the H and N proteins found on the virus's surface. Currently, 16 types of H proteins and 9 types of N proteins are known. When referring to a strain such as H1N1, the "H1" and "N1" denote the specific types of these surface proteins.
