Viral pathogenesis refers to the process by which viruses cause disease in a host organism. It involves several stages, including viral entry, replication, and spread within the host. Once inside, viruses can evade the immune system, leading to cell damage and inflammation, which contribute to the symptoms of illness. The severity of viral pathogenesis can vary based on factors such as the type of virus, the host's immune response, and the presence of underlying health conditions. Understanding viral pathogenesis is crucial for developing effective treatments and vaccines against viral infections, such as influenza or HIV.