The general human disease-causing viruses may come from animals or their own latent viruses. Virus structure is simple, only contains a nucleic acid, must be parasitized in living cells, generally lead to human disease virus is mostly from animals, or their own latent virus. 1. Animals: Some animal viruses are common viruses for humans and animals, and animals carry viruses for transmission, such as mosquitoes carry West Nile virus, which spreads through biting humans, and infected with the virus, the human body will develop West Nile virus disease. 2. own latent virus: part of the virus can be latent in the body after infection, when the body’s immune function is low, only when the clinical manifestations, the more common herpes virus, chickenpox virus, herpes simplex virus, cytomegalovirus, EBV and so on.