Smallpox is a very serious disease; it is contagious and sometimes fatal. Smallpox is caused by a germ called variola virus.
The symptoms of smallpox begin with high fever, head and body aches, and sometimes vomiting. These symptoms are followed by a rash that spreads from the head and extremities toward the center of the body, then progresses to raised bumps that eventually scab over and fall off after about three weeks, leaving a pitted scar.
Smallpox can cause:
Natural cases of smallpox have been eradicated. The last natural case of smallpox was in Somalia in 1977.
The incubation period for smallpox is about 12 to 14 days (range: 7 to 17 days) after exposure.
The disease usually requires face-to-face contact with a contagious person for several hours. Contact with infected skin could also transmit the virus. Spread by contact with inanimate objects (e.g., clothing, towels, linens) would be less common.
People with smallpox are contagious from when their temperature goes over 101°F (38.3°C). They stay contagious until all their scabs fall off.
Not everybody who talks with a smallpox patient will get the disease. People with smallpox can infect about half of the people who live in their household. On average, each infected person can infect about 5 other people. Those other people show symptoms about 15 days after exposure.
The most common way to transmit smallpox would be from prolonged face-to-face contact. People infected with smallpox exhale little droplets that carry the virus to the nose or mouth of bystanders. The greatest risk comes from prolonged face-to-face contact (6 feet or less, most often after 1 or more hours), with an infected person, especially one who is coughing. Indirect contact through fine-particle aerosolization or contaminated inanimate objects can spread the virus as well, though less efficiently.
Special precautions need to be taken to thoroughly clean all bedding and clothing of smallpox patients with bleach and hot water. Disinfectants such as household bleach or hospital-approved quaternary ammonia disinfectants can be used for cleaning contaminated surfaces.
Animals and insects do not carry or transmit smallpox disease. Smallpox is not spread by food or water.