What are the Causes of Smallpox?

Smallpox is caused by infection with variola virus. After infection, the virus divides inside your body (initially in the lymph nodes and then in the spleen and bone marrow). The virus in due course of the disease reaches the blood vessels in your skin and the mucous membranes of your nose and throat and settles there. Sloughing of the lesions in the mouth releases large amounts of virus into your saliva. This makes you infective and you're most likely to transmit the disease.

The way smallpox spreads: Smallpox mostly spreads by droplets. When an infected person coughs, sneezes or talks, the virus is released in the droplets of cough, sneeze or saliva. People in direct contact with the infected person are likely to catch the infection.

Under rare circumstances, the airborne virus may spread through ventilation/air-conditioning systems in a building and infect people in other rooms of the building. Sometimes smallpox can also spread through contact with contaminated clothing and bedding.

Types of Smallpox

There are two main forms of smallpox:  Variola minor and Variola major.

• Variola minor is the milder form of the disease and is rarely fatal (causes death in less than 1 percent of people who are infected).
• Variola major is a more severe form of illness which kills one-third of the people it infects.

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