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Smallpox is an acute, highly infectious viral disease that can lead to death or complications. It has killed more people over the course of history than any other infectious disease. It cannot be treated but can be prevented by vaccination.
The virus
The name smallpox comes from the Latin word for “spotted”, referring to the raised bumps and lesions that appear on infected persons. In old English, it was referred to as “small pockes” (meaning sac), thus leading to the now common name of smallpox. The variola virus, which causes smallpox, is a member of the orthopoxvirus family. There are two clinical forms of smallpox:
- Variola major: the most severe and most common type of smallpox (accounting for more than 90% of cases), with a fatality rate of 30%.
- Variola minor (or alastrim): a milder version of smallpox, with a death rate of 1% or less.
Transmission
The variola virus spreads from person to person. It is generally transmitted by aerosols and the droplets in an infected person’s breath. It can also be spread through direct contact with infected bodily fluids and contaminated objects such as bedding and clothing.
The virus has an incubation period of 7-17 days. During this period an infected person looks and feels healthy and cannot transmit the virus to others. However, this changes when the infected person moves into the sudden onset of fever (prodrome stage), followed by development two to three days later of a rash of sores all over the body. It is during this period that a person is most contagious. Sores that have also developed in the mucous membranes of the mouth and nose break open. Large amounts of the virus are then released into the respiratory tract of the infected person, and his or her breathing or coughing sends the virus into the air. The patient remains infectious to others until the end of the fi nal disease stage: when the last scab falls off.
Thirty percent of infected persons die during the course of the disease. Those that do survive are immune to the disease for the rest of their life but often subject to devastating complications. It is estimated that between 65-80% of survivors are marked with deep-pitted scars (pockmarks), mostly found on their face. Blindness, another complication of the disease, reached levels of 90% in some outbreaks during history.
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