MILWAUKEE (AP) _ Monkeypox, a less deadly relative of smallpox, kills up to 10 percent of its victims in Africa. Yet a monkeypox outbreak two years ago in the United States killed no one, and scientists have wondered why.
Now they have a good idea. New research finds that there are two distinct strains of the virus, and that the U.S. outbreak involved the weaker West African one rather than the more deadly Congolese one. The illness was spread by prairie dogs after they were infected by imported African rodents at a pet distribution center.
``If it had come from Congo, we might have had a bigger problem on our hands and very well might have seen patient deaths,'' said Mark Buller, a St. Louis University virologist who led the federally funded study, published Friday in the journal Virology.
Scientists from the U.S. Army Research Institute of Infectious Diseases, the Centers for Disease Control and Prevention, and four other universities in the United States and Canada worked on the report.
The monkeypox outbreak two summers ago was the first in the Western Hemisphere. An estimated 72 people throughout the Midwest were sickened by the virus, which causes blisters and a rash that resemble smallpox.
Cases were reported in Wisconsin, Illinois, Indiana, Kansas, Ohio and Missouri. Sixteen people were hospitalized, though not all were sick. Two children required intensive care and recovered.
Doctors thought better U.S. medical care and generally better health than in Africa were the reasons no one died. But genetic analysis suggests the germ itself made the difference.
Researchers compared several strains similar to the West African one in the U.S. outbreak to a Congolese strain from a gene bank.
They also looked back at previously unpublished experiments Army researchers had done in the 1990s on such viruses in monkeys as part of an effort to find ways to test new smallpox vaccines.
Monkeys infected with the West African strain got only mildly ill and none died. Five out of six of those given the other strain got severely ill and all three that got the higher dose of it died.
After the 2003 outbreak, federal officials banned the importation of African rodents and the sale of U.S. prairie dogs, but importing animals from other countries is still legal, along with breeding captive exotic and wild animals.
``We definitely are better off than we were'' before the outbreak in terms of regulation, said
Dr. Marty Cetron, the CDC's director of quarantine, but he added, ``there's still more that could be done.''
``We do think there is a risk of emerging infections being spread by or amplified by the exotic pet trade,'' he said.