Smallpox is a DNA virus, the full name is called smallpox virus, belongs to a poxvirus. Smallpox virus infection caused by the disease is called day but in the continuous process of natural evolution gradually mutated to form a large number of people can be infected in the population, and produce serious harmful smallpox virus, flower, initially is not harmful to the human body of the type of virus, there are mainly three types of subtypes, that is, large smallpox, small smallpox in smallpox three kinds of disease and infectious way exactly the same, the lethality decreasing in turn. Smallpox virus is a kind of DNA virus, its genetic material is DNA, can be transmitted through the air, in the history of once had an outbreak of pandemic, and later due to cowpox inoculation is effective in preventing smallpox, coupled with smallpox vaccine was introduced, smallpox virus has been basically extinct in China at present.