What is smallpox?
Smallpox is an acute contagious disease caused by the smallpox (or variola) virus. There are 2 forms of the disease, variola major (ordinary form) and variola minor (alastrim). In the past smallpox was a very common cause of illness and death (especially in children). In unvaccinated people the mortality rate was about 30%. However, following a worldwide vaccination campaign, coordinated by the World Health Organization smallpox was declared eradicated in 1980. The last naturally occurring case was identified in Africa in 1977. There are no animal reservoirs for the infection.

If smallpox is eradicated why is there a concern about it?
Attempts have been made in the past to weaponise smallpox, making it into a mist that could be inhaled and so mimicking on a large scale how smallpox was spread naturally. While the risk of a deliberate release of smallpox virus is very low, there are several factors which contribute to the bioterrorism potential of this virus; high mortality rate, transmission from person-to-person, lack of effective treatment, and declining numbers of vaccinated people (in general, vaccinated people are at least 30 years of age now).

How is smallpox spread?
Smallpox is most often spread by inhaling virus particles through close contact with an infected person (generally family members), but transmission via clothes and bedding is also possible.

How infectious is smallpox?
Smallpox is moderately infectious. In families about half of all family members were likely to become infected.  Patients become infectious at the very onset of symptoms (it may not be recognised as being smallpox at this stage). A patient is most infectious during the first two weeks of illness. The incubation period for smallpox is usually 10-14 days but may vary between 7-19 days. The rash starts to appear about 2 days after the first symptoms (taken as the onset of fever).

What are the symptoms of smallpox?
Onset of smallpox is sudden with fever, headache, feeling poorly and an aching head and back; patients are usually bedridden. A macular (small spots) rash develops over the next 1-2 days into papules (raised spots). By days 4-5 vesicles (fluid filled spots) appear all over the body, particularly on the face, arms and legs, and also in the mouth and throat. These become pustules (infected spots) after about 7 days. Scabs form around 14 days and separate at 4 weeks leaving permanent scars.

What is the treatment for smallpox?
There is no specific treatment for smallpox, management being supportive. New antiviral drugs show some promise in the treatment of viruses like smallpox. Cases are isolated to prevent further spread.

Can smallpox be prevented?
Yes, and quite easily. There is a very effective vaccine against smallpox which is not administered anymore since smallpox has been eradicated. Vaccination can cause serious side effects and it should not be given to pregnant women, those with weakened immune systems, or those with eczema. However, vaccination given up to 4 days after exposure can reduce the severity of the disease and can reduce mortality.

Created: 8th July 2010

Last reviewed: 15th February 2016