Monkeypox Startles Midwest

Outbreak raises fears that virus could become established in the U.S.

Pox Americana. The monkeypox virus (inset) causes vesicular lesions among its first human patients in the Western hemisphere.

A sudden outbreak of monkeypox in three Midwestern states has surprised virologists and public health officials. They are concerned that the virus could get a foothold among wild animals or pets in North America, posing a permanent threat to human health. The Centers for Disease Control and Prevention (CDC) in Atlanta is currently investigating 33 potential human cases of the disease; there have been no fatalities so far.

Monkeypox, a relative of smallpox, occurs primarily in the rainforests of Central and West Africa. Besides monkeys, several rodent species, and rabbits, it is known to infect humans, killing between 1% and 10% of patients. Its symptoms, including a rash, pustules, and fever, resemble those of smallpox, although they tend to be less severe.

Most of the patients now seen in Wisconsin, Illinois, and Indiana appear to have acquired the disease from sick prairie dogs, which they had recently purchased as pets. An investigation has traced the animals back to an animal distributor in Milwaukee, Wisconsin, who sold the animals to two pet shops and at a "pet swap meet"--where animals are sold or bartered--in northern Wisconsin. The distributor had bought the prairie dogs--as well as a sick Gambian giant rat that may have the source of the virus--from an animal distributor in northern Illinois, CDC says.

One reason monkeypox worries researchers is that some have speculated it may evolve to transmit more easily between humans and fill the ecological niche left after the eradication of smallpox (Science, 18 July 1997, p. 312). But there's no evidence that that is happening, says epidemiologist Joel Breman of the Fogarty International Center in Bethesda, Maryland, and a former director of poxvirus studies at the World Health Organization. There have been no known cases of human-to-human transmission in the current outbreak, CDC's Stephen Ostroff said during a news conference today.

Researchers and public health officials do worry that the virus might establish itself in wild rodents and then keep infecting new victims. It's not that hard to imagine, warns Peter Jahrling, a poxvirus researcher at the U.S. Army Medical Research Institute of Infectious Diseases in Fort Detrick, Maryland: "When Johnny's pet gets sick and Mommy doesn't want to take him to the vet, she may release him into the woods." Investigations are currently going on to retrace as many potentially infected animals as possible, says pathologist Kurt Reed of the Marshfield Clinic in Marshfield, Wisconsin, where three patients are being treated: "We're still hoping this is a one-shot deal for the history books."

Related sites
CDC information about the monkeypox outbreak
More from the Marshfield Clinics in Wisconsin
Paper in Emerging Infectious Diseases about the 1996-97 outbreak in the Democratic Republic of the Congo
More about prairie dogs

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