Suspected cases of the previously eradicated disease smallpox in eastern Uganda appear to be chickenpox and not the acute contagious disease, the World Health Organisation said on Thursday.
"It appears that the supposed cases of smallpox are actually cases of chickenpox, and that they have occurred over the past three weeks — this is not an acute event," WHO spokesman Gregory Hartl said in a statement. "WHO has communicated this latest information to its member states."
The WHO said earlier on Thursday it was investigating reports of suspected cases of smallpox in eastern Uganda.
Smallpox can sometimes be confused with chickenpox, a worldwide infection of children that is very rarely dangerous.
Smallpox kills around 30 percent of its victims and was one of the world's most feared sicknesses until it was officially declared eradicated worldwide in 1979.
The United States and other countries have built up stockpiles of vaccines to deal with any threat.
The U.S. Centers for Disease Control and Prevention says on its Web site that there are concerns smallpox could be used for bioterrorism.
Laboratory accident
The last known natural case of smallpox was in Somalia in 1977. Since then, the only known cases were caused by a laboratory accident in 1978 in Birmingham, England, which killed one person and caused a limited outbreak.
Makers of smallpox vaccine include Sanofi Pasteur, the vaccines division of Sanofi-Aventis, and Denmark's Bavarian Nordic.
Smallpox, which is believed to have originated more than 3,000 years ago in India or Egypt, is described by the WHO as "one of the most devastating diseases known to humanity."
The incubation period usually lasts from 12 to 14 days, followed by the sudden onset of flu-like symptoms including fever, headache, severe back pain, abdominal pain and vomiting. Two to three days later pox, or lesions, start to appear first on the face, hands and arms and then on the trunk.
The pox ulcerate quickly, releasing large amounts of virus into the mouth and throat. The most severe cases involve hemorrhage, or bleeding, into the mucous membranes and skin.
Chickenpox produces much more superficial lesions which tend to appear more on the trunk than the face or hands.
