Causes

Smallpox is caused by infection with the variola virus. The virus can be transmitted:

• Directly from person to person. Direct transmission of the virus requires fairly prolonged face-to-face contact. The virus can be transmitted through the air by droplets that escape when an infected person coughs, sneezes or talks.
• Indirectly from an infected person. In rare instances, airborne virus can spread farther, possibly through the ventilation system in a building, infecting people in other rooms or on other floors.
• Via contaminated items. Smallpox can also spread through contact with contaminated clothing and bedding, although the risk of infection from these sources is less common.
• As a terrorist weapon, potentially. A deliberate release of smallpox is a remote threat. However, because any release of the virus could spread the disease quickly, government officials have taken numerous precautions to protect against this possibility, such as stockpiling smallpox vaccine.