Viruses can cause cell death by direct invasion of host cells and continuous replication within the cell. The manifestations due to viral infection depend on the type of virus, and its specific affinity for a particular tissue or cell. The specific disease features that appear need to be determined by the location of viral infestation, such as the digestive system, respiratory system, nervous system, or individual organs, which may all have different features. However, common features include fever, inflammation and tissue necrosis: 1. Fever: When a patient is infected by a virus due to a decrease in their own immunity, the function of the thermoregulatory center is affected, causing it to become impaired, resulting in a fever in the organism. In addition, after virus infection, the body will produce corresponding inflammation, when its own defense system will resist the abnormality at the inflammation by fever; 2. Inflammation: When the virus invades certain systems or organs of the body, it will destroy the cells of local tissues, thus causing local inflammation; 3. Tissue necrosis: When the inflammation keeps developing and is not treated in time, it will lead to the situation of necrosis on the surface of tissues or organs. In addition, HIV infection can destroy the autoimmune system, hepatitis B virus infection can affect the liver, and influenza virus can cause respiratory symptoms, such as sore throat, coughing and phlegm or even affect normal breathing. Some viral infections can result in lifelong immunity, such as chickenpox and measles, and skin symptoms are mostly itching and herpes. When the virus invades the gastrointestinal tract, it causes nausea, vomiting, abdominal pain, and diarrhea. The symptoms of viral infection can be mild or severe. Patients are advised to seek active treatment to avoid other complications or irreversible damage.