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U.S. Monkeypox Outbreak Traced to Wisconsin Pet Dealer

Science
13 Jun 2003
Vol 300, Issue 5626
p. 1639
The field of infectious diseases can't stay off the front pages these days. No sooner do reports of SARS subside than a new surprise comes along: Monkeypox, a cousin of smallpox that normally dwells in the rainforests of Western and Central Africa, has popped up in towns in three states in the U.S. Midwest, infecting pet prairie dogs and their owners. It is the first time that a monkeypox outbreak has been seen in the Western Hemisphere.
As Science went to press, four people had been diagnosed with the disease, and another 33 possible cases were being investigated. Although monkeypox historically has killed 1% to 10% of its human victims, none of these patients has died. The epidemic, coinciding with the start of the U.S. West Nile season, had public health officials and virologists reeling, and, once again, changing tack. “SARS was the virus du jour,” says poxvirus expert Peter Jahrling of the U.S. Army Medical Research Institute of Infectious Diseases in Fort Detrick, Maryland. “Now, it's taking a back seat.”
The virus in this outbreak was first isolated and recognized as an orthopoxvirus last week by Kurt Reed, a pathologist at the Marshfield Clinic in Marshfield, Wisconsin; subsequently, samples were rushed to the Centers for Disease Control and Prevention (CDC) in Atlanta, where genetic tests nailed it as the monkeypox virus on 7 June.
Index case.
After being bitten by a sick prairie dog, a child in Wisconsin developed monkeypox.
CREDIT: MARSHFIELD CLINIC
In a report posted on its Web site, CDC says that the first patients got sick in early May, which led some experts to wonder why, in an era of smallpox jitters, it took more than a month to recognize a disease with symptoms similar to those of smallpox. But Wisconsin state epidemiologist Jeffrey Davis says the first patient—a young girl—didn't become ill until 15 May; besides, he says, she developed a rash on her finger after a bite from her prairie dog, so plague and tularemia, both carried by the critters, were more likely candidates. “The Marshfield did everything extraordinarily rapidly,” Davis says.
Monkeypox derives its name from a series of outbreaks among lab monkeys in the 1950s and 1960s, but the virus is known to infect other primates, several rodent species, and rabbits as well. Its natural reservoir is still unknown, but squirrels are prime suspects, says Joel Breman, a former poxvirus research director at the World Health Organization who is now at the Fogarty International Center in Bethesda, Maryland.
Almost all of the suspected monkeypox patients in Wisconsin, Illinois, and Indiana appear to have contracted the disease from prairie dogs that they had recently purchased as pets. An investigation has linked all the sick animals back to a distributor in Milwaukee, Wisconsin, who sold animals to two pet shops and at a “pet swap meet” in northern Wisconsin. The distributor also had owned a sick Gambian giant rat, which may have been the source of the virus, CDC says.
Humans have become much more susceptible to orthopoxviruses after smallpox vaccination was halted worldwide in the 1980s. Monkeypox has been a particular concern; some scientists worry that the virus may fill the niche vacated by smallpox if it evolves and becomes more readily transmissible among humans. That fear was fueled by an 1996–97 outbreak in the Democratic Republic of the Congo in which human transmission appeared to be very prevalent (Science, 18 July 1997, p. 312). But there's no evidence yet that monkeypox is replacing smallpox, Breman says, and there are no known cases of human-to-human transmission in the current outbreak.
It would be bad enough, however, if the virus became established among U.S. pets or wild animals, creating yet another permanent human health hazard. That's why authorities are now feverishly trying to trace every infected prairie dog, says Davis, hoping none of them will be released into the wild. To gauge the potential for spread in pets, Jahrling is planning to study hamsters' and gerbils' susceptibility to the virus. Says Reed: “We're still hoping this is a one-shot deal for the history books.”

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Science
Volume 300 | Issue 5626
13 June 2003

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Published in print: 13 June 2003

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