A viral disease is a condition caused by the invasion and reproduction of viruses in the human body or living organisms. Viruses are microorganisms that require host cells to multiply and can trigger an immune response. When a virus enters the body, it triggers an immune system reaction, which involves defense cells and molecules. Although this immune response is essential to control the viral infection, some viruses can evade it and weaken the immune system, which can lead to persistent or chronic infections in certain cases. A chronic viral disease persists in the body for a long period, often years or even the entire life of the infected individual. These diseases can be asymptomatic for a long time and can manifest in the form of relapses or intermittent outbreaks.
The prevalence of viral diseases varies depending on the populations and the data sources used. A general global prevalence estimate in millions for some of these diseases is provided below:
