Unraveling the Monkeypox Mystery

Doctors piece together virus' advance from Africa to America

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HealthDay Reporter

WEDNESDAY, Jan. 21, 2004 (HealthDayNews) -- When a 3-year-old Wisconsin girl was hospitalized last year with a fever and a lesion on her finger where she had been bitten by a prairie dog, Dr. Kurt D. Reed knew he was dealing with an infection of some type.

It quickly became clear, however, that the girl had no ordinary bacterial infection, which is most common after an animal bite. Nor did her mother and father, both of whom also fell ill.

Doctors ruled out plague and tularemia, two types of bacteria that are known to infect prairie dogs and could possibly be transmitted to humans. And the symptoms didn't match up with rabies, which can also be acquired from an animal bite.

When bacterial cultures turned up negative, the doctors turned their attention to finding some type of virus.

A sample from a lesion found on the mother was put under an electron microscope and diagnosed as a pox virus.

"Then it got to be very confusing right away," says Reed, lead author of an article detailing this novel investigation that appears in the Jan. 22 issue of the New England Journal of Medicine. "There wasn't much in the medical literature about prairie dogs having pox viruses at all."

At the time, Reed and his colleagues also thought they were dealing with isolated cases. "By that time, the child was out of the hospital recovering, the mother was never in the hospital and they had a relatively mild illness," Reed says. "We were thinking this is really an interesting, unusual case, but we didn't feel we had an outbreak on our hands."

In fact, Wisconsin and other Midwestern states did have an outbreak -- of monkeypox spread by contact with pet prairie dogs. In all, there were 72 suspected cases and 37 confirmed cases in humans during May and June of 2003. All were linked to one distributor who had received a shipment of prairie dogs that had traveled with a Gambian giant rat that originally came from Africa.

"That's when a very unclear picture came into sharp focus over the course of just a couple of hours," Reed says. The geographical range of the Gambian rat matched that of monkeypox.

Monkeypox was first recognized in 1958 in monkeys. The first human cases were reported in Zaire in 1970, and there have been sporadic outbreaks since then, all of them in Africa.

Last year's Midwestern outbreak was notable not only because it was the first instance of humans being infected outside of Africa, but also because of what it might portend for the future.

"This is another reaffirmation of what we see time and time again when we introduce animals into a new area that they've never been in," says Dr. John Zaia, chairman of virology at the Beckman Research Institute at City of Hope National Medical Center in Duarte, Calif.

"Here we actually import animals that are potentially infected, introduce them into a population that is totally naive in terms of infection, and see not only the potential [for] spread [of disease] in indigenous animals in the area, but also [in] humans... It is the shrinking world that allows this sort of thing to happen," he says.

"If we continue to import animals from parts of the world that have these infections, then, of course, this could happen again. That's why they made state and federal bans on importing rodents from Africa," Reed adds.

But it's not only imports that could be a problem. What happens if native North American species, such as mice or squirrels, become infected and start passing the disease on?

There's no evidence that this has happened, but it is a concern. "We have put a lot of effort into trying to determine if that actually took place," Reed says. "This is a virus that our animal species in North America haven't been exposed to, so certain species would have a high fatality rate. If you had enough viral activity, there would be continued potential exposure to humans."

More information

For more on monkeypox, visit the U.S. Centers for Disease Control and Prevention and the World Health Organization.

SOURCES: Kurt D. Reed, M.D., infectious disease pathologist, Marshfield Clinic Research, Marshfield, Wisc.; John Zaia, M.D., chairman, virology, Beckman Research Institute, City of Hope National Medical Center, Duarte, Calif.; Jan. 22, 2004, New England Journal of Medicine

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