Smallpox was a highly contagious human disease caused by the variola virus. There are two strains: variola major, with severe symptoms and a very high mortality (20-40%), and variola minor, with less severe symptoms and lower mortality (about 1%).

In 1967 the World Health Organization embarked on a World Eradication Program. In the preceding year, 10-15 million people had died of smallpox.

The last recorded natural case occurred in Somalia in 1977, but laboratory exposure has caused several small epidemics since. The last case in this country was in September 1978. An English laboratory accident exposed a 40-year-old medical photographer named Janet Parker to smallpox -- an incident that has lent support to arguments to destroy the remaining vials. Parker died. Her death had a ripple effect: The virologist in charge of the laboratory at the University of Birmingham felt so responsible for her death that he committed suicide.

The WHO declared the disease eradicated in 1980.

Smallpox is documented in literature dating back centuries though most people in the Western world would have difficulty in remembering a case.

Transmission occurs through droplet infection (coughs and sneezes) within a household, but only from someone who is obviously ill The virus passes through the respiratory tract, local lymph nodes and then enters the blood. Internal organs are infected next and then the virus re-enters the blood and spreads to the skin. These events occur during the incubation period (about 12 days), when the patient is still well.

The rash is the result of virus replication in the skin.

Immunity following smallpox is permanent; immunity after vaccination lasts up to ten years.

Early symptoms include

  • Sudden onset of fever
  • Headache
  • Backache
  • Vomiting
  • Inability to stand (prostration)
  • Delirium
10% of patients may exhibit a fleeting rash in the form of a reddening of the skin, not unlike the rash of German Measles. It would not be possible to diagnose smallpox at this stage from this early rash. After 2-3 days this early rash will settle and the true rash of smallpox will appear. This is diagnostic in the way it develops and in its distribution on the skin.

The rash starts as tiny discrete pink spots (macules), which enlarge and become slightly raised (papules).

Each of these progresses by the third day to become a tense blister, (known as vesicle) 6mm in diameter, deep in the skin. After a couple more days the fluid inside becomes cloudy and the lesions are described as pustules or by the older term of pocks. These then crust over; the crusts eventually falling off leaving a deep scar. The crusts contain the virus.

The distribution of this focal rash is characteristic, affecting the head, face arms and legs much more than the trunk. This distribution distinguishes it from chickenpox where the rash is found more on the body than the arms and legs. The blisters in chickenpox are much more shallow, thus leaving less in the way of disfiguring scars.

The toxic effects of the virus can cause death and can be correlated with the severity of the rash to a degree. The rash can cover the whole body in very severe cases. Sometimes the illness can be so severe as to cause death before the rash is fully developed. Death usually occurs on day 11-15 of the rash.

Vaccination programmes have ceased in the general population due to the eradication of the illness. Edward Jenner was famous for his discovery of the concept of vaccination due to his observation that individuals who had been affected by cowpox seemed to be immune to smallpox. In 1796 he successfully vaccinated some 24 children.

Smallpox is still kept in a few laboratories around the world although there have been calls for its destruction. It would be a favoured agent for germ warfare due to the lack of immunity in the worldwide population. Some lab workers and servicemen are still offered vaccination.

Further information

This article published on
26 January 2006

Next review date 1/1/2013


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