Smallpox (small pox) is a virulent infectious disease caused by the smallpox virus that infects people and provides lifelong immunity after recovery. Smallpox is one of the oldest and most deadly infectious diseases, highly contagious, heavy disease, no smallpox or smallpox vaccine people can be infected, mainly manifested as a serious viral blood disease, high mortality after contracting the disease. The most basic and effective and the easiest way to prevent it is to receive cowpox. Smallpox clinical manifestations of heavy and light, heavy smallpox mortality rate of about 25.5%, 45% of cases appear fusion rash, 79% have bleeding phenomenon; light smallpox mortality rate of 0.1% to 1.0%. Smallpox virus is a kind of pox virus, people are infected with no special drugs can be treated, patients in the face after recovery will be left with pockmarks, “smallpox” thus named. The smallpox virus is brick-shaped, about 200 nm x 300 nm, and is resistant to dryness and low temperatures, and can survive for months to a year and a half on scabs, dust, and clothing. Causes of smallpox The smallpox virus invades the body mainly through the mucous membranes of the respiratory tract and is transmitted through droplet inhalation or direct contact. Smallpox virus has two strains of viruses with different virulence, the virulent ones cause positive smallpox, i.e. typical smallpox; the weak ones cause light smallpox, i.e. smallpox-like.