Smallpox transmission generally occurs through face-to-face contact, direct contact with contaminated fluids and objects, and rarely, through the air. When someone becomes infected, he or she will generally not feel sick for 10 to 12 days, even though the smallpox virus is multiplying in the body. The period between smallpox transmission and the beginning of smallpox symptoms is known as the incubation period.
Smallpox transmission can happen in one of several ways:
- Face-to-face contact
- Direct contact with infected fluids and contaminated objects
- Through the air.
Humans are the only natural hosts of variola (the virus that causes smallpox). Therefore, smallpox transmission does not occur through animals or insects.
Smallpox is a highly contagious disease. In most cases, smallpox transmission occurs by inhaling droplets of saliva, which are full of virus, during face-to-face contact with an infected person. Usually, fairly prolonged face-to-face contact (lasting 3 or more hours) is required.
Smallpox transmission can also occur through direct contact with infected bodily fluids or contaminated objects such as bedding or clothing. Those caring for people with smallpox need to use special safety measures to ensure that all bedding and clothing from the infected person is cleaned appropriately with bleach and hot water. Caretakers can use disinfectants such as bleach and ammonia to clean contaminated surfaces.
Through the Air
Rarely, smallpox has been spread by virus carried in the air (aerosolized) in enclosed settings such as buildings, buses, and trains. The smallpox virus is fragile. In laboratory experiments, 90 percent of aerosolized smallpox virus dies within 24 hours; in the presence of ultraviolet (UV) light, this percentage would be even greater. If an aerosol release of smallpox occurs, 90 percent of virus matter will be inactivated or dissipated in about 24 hours.