Smallpox Dr Rob Hicks This highly infectious disease was once one of the most feared diseases, killing an estimated 300 million people worldwide in the 20th century. We look at how it's now treated.

In this article

What causes it? What are the symptoms?

Who's affected? How's it prevented?

What's the treatment?

Smallpox infection is caused by the variola virus and is highly infectious. It's most often spread by inhaling virus particles from an infected person.

The incubation period between infection and the appearance of symptoms is between seven and 17 days.

People don't become infectious until they develop symptoms. They're most infectious during the first two weeks.

Smallpox kills around one in three of those who become infected.

The initial symptoms of smallpox are fever, muscle aches, headache, vomiting and tiredness. Over the next one or two days, the distinctive smallpox rash appears all over the body. The rash develops into vesicles (small, fluid-filled blisters), particularly on the face, arms and legs, but also in the mouth and throat. These crust and fall away after three to four weeks.

The last case of smallpox caught in the community was in 1977.

Smallpox was declared eradicated worldwide in 1980 following successful immunisation programmes.

Effective vaccines are available to protect people from smallpox infection.

There's no specific treatment for smallpox infection. Treatment is of the specific symptoms and is supportive.

This article was last medically reviewed by Dr Rob Hicks in July 2006.