👉 A virus is a type of infectious organism that causes disease in humans and animals. It has two main types: RNA viruses, which are the most common, and DNA viruses, which can also cause diseases if they enter the body through infected cells. Viruses have a single gene that encodes for proteins called nucleocapsids, which make up the outer shell of the virus. The genetic material of the virus is contained in the nucleocapsid, which is surrounded by a protein coat (