U.S. monkeypox outbreak a weaker strain: study

An outbreak of monkeypox virus in the U.S. was less deadly than feared because the strain was a weaker version, scientists say.

Monkeypox is a viral disease related to smallpox but is less infectious. Although it kills up to 10 per cent of its victims in Africa, no one died in the 2003 outbreak in the U.S.

Symptoms include fever, pus-filled blisters all over the body and respiratory problems.

Now scientists have a solution to the medical mystery of why fewer people died than expected. A genetic analysis shows there are two different strains of the virus, researchers report in the July issue of the journal Virology.

"We have at least two biological strains of monkeypox virus – one on the west coast of Africa, and the other in the Congo basin," said virologist Mark Buller of Saint Louis University Health Sciences Center.

"The 2003 outbreak in the United States was from West Africa. If it had come from Congo, we might have had a bigger problem on our hands and very well might have seen patient deaths," he added in a release.

Monkeypox is a zoonosis, an animal disease that can be spread to humans.

As humans move into animal habitats, scientists say zoonoses are more likely to be transmitted to people. That's why cases of monkeypox in Africa are thought to be on the rise, Buller said.

An estimated 72 people in the U.S. Midwest were sickened by monkeypox virus in 2003. There were no documented cases of human-to-human transmission.

The U.S. Centers for Disease Control traced the outbreak to a shipment of prairie dogs sent to a wholesaler in Texas. The animals were infected by a Gambian rat imported from Africa.

The CDC has since banned shipments of exotic pets, including rodents from Africa that can carry monkeypox, as well as prairie dogs.