Infectious diseases caused by viruses that can reproduce parasitically in the human body and cause disease. The main manifestations are systemic symptoms of toxicity such as fever, headache, general malaise and local symptoms caused by inflammatory damage due to the virus host and invasion of tissues and organs. There are two types of infections, most of which are occult (subclinical infections), while a few occur as overt infections. Overt infection can be divided into two types: acute infection and persistent infection. 1, acute infection: the onset of acute, rapid progress, the course of the disease is generally a few days to a few weeks. Except for a small number of deaths and sequelae during the acute phase, most cases are eventually cured by the clearance of the virus from tissues and organs. 2, persistent infection: the virus exists in the host body for a long time, which can be several months to years, resulting in chronic persistent infection, and can be divided into the following three types: (1) latent infection. When the virus and human immunity is in a relative balance, the virus can be long-term latent in human tissue, does not cause symptoms. Once the body’s immunity is reduced, the virus can repopulate and cause symptoms. Examples include latent infections caused by herpes simplex virus, EBV and varicella-zoster virus. (2) Chronic infection. Virus exists in human tissues and organs for a long time, causing chronic persistent lesions, such as chronic hepatitis B caused by hepatitis B virus. (3) Lentiviral infection. The incubation period is long, up to several years, and the lesions develop gradually, eventually leading to death. Aplastic anemia is a group of bone marrow hematopoietic failure syndromes caused by various etiologies, characterized by hypoplasia of bone marrow hematopoietic cells and reduction of peripheral blood cells, with anemia, bleeding and infection as the main clinical manifestations. The exact cause is not yet clear, but the development of reoccurrence may be related to chemical drugs, radiation, viral infection and genetic factors. The reoccurrence is mainly seen in young adults, and there are 2 peak periods of its incidence, namely the age group of 15-25 years and the older age group of 60 years and above. The incidence is slightly higher in males than in females. According to the severity of bone marrow failure and the progression of clinical course, it is classified into heavy and non-heavy remitting disease as well as acute and chronic remitting disease.