Future Tense

What Happened the Last Time There Was a Monkeypox Outbreak in the U.S.

A prairie dog peeks out of a hole.
A prairie dog (presumably not infected with monkeypox) at the San Francisco Zoo. Justin Sullivan/Getty Images

On Tuesday, the World Health Organization announced that it is continuing to investigate the recent outbreak of monkeypox but believes it is “containable.” As Slate’s Jordan Weissmann has explained, monkeypox is a virus related to smallpox that causes flu-like symptoms and skin lesions. Rarely found outside of Africa, it’s been making headlines after an outbreak that, according to a tracker from the data science initiative Data.Health, has grown to more than 300 confirmed and suspected cases in places where it isn’t endemic, including the U.S., the U.K., Canada, and several European countries.

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While it’s perfectly understandable to be anxious about another viral outbreak after the past few years we’ve had, public health officials have said that risk to the public is low. And although he originally said monkeypox is something “everybody should be concerned about,” President Joe Biden said on Monday that a national quarantine would not be necessary to contain monkeypox cases in the U.S. because there are enough vaccine doses to prevent a widespread outbreak. Monkeypox has historically been prevented using smallpox vaccines, which are not currently available to the general public in the U.S., but there is a reserve in case of emergency. The FDA also approved a vaccine to prevent monkeypox in 2019.

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And the U.S. has faced monkeypox before, most notably in July 2003, when 47 individuals from six Midwestern states—Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin—were confirmed to have or suspected of having the West African strain of the monkeypox virus (the same strain that has broken out in the U.S. and Europe this year). The outbreak began in Illinois, where an exotic animal vendor received a shipment of Gambian pouched rats and briefly housed them next to a prairie dog enclosure. The Gambian pouched rats were infected with monkeypox—which, despite its name, is more common in rodents than in monkeys—and passed it along to their neighbors.

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Before the prairie dogs showed any signs of infection, they were sold as pets to both individuals and to pet shops, where their rapid and widespread distribution led to 71 total confirmed cases. (That’s human and animal infections.) One unfortunate family, the Kautzers, had bought two during a Mother’s Day event. After they got sick, they were told to quarantine “until the scabs fall off the sores,” and while one of their prairie dogs eventually succumbed to the illness, they were happy to keep the second (named Chuckles!) after he recovered.

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During the outbreak, the smallpox vaccine was used both to prevent further transmission and to help infected individuals fight off the monkeypox. At least 30 people received the vaccine, either pre- or post-exposure, as the smallpox vaccine can “make the disease less severe” if administered within a week of exposure, according to the CDC.

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Kurt Zaeske, a veterinarian who contracted one of the first cases during the 2003 outbreak, told Insider recently that he noticed younger infected people tended to have worse symptoms and more lesions than older people. He theorized that this was due to the discontinuation of regular smallpox vaccinations in 1972, as a result of the eradication of the virus within the U.S. Older individuals who had been vaccinated against smallpox would have had some natural immunity to monkeypox because of the similarities between the two viruses.

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The difference between the 2003 outbreak and the recent one is the ways in which the virus can be transmitted. According to the CDC, the virus can be passed from person to person, and appears to be spreading through breathing in large respiratory droplets as well as by touching  the skin lesions of an infected person, both of which require close, prolonged contact with an infected person. It can also be contracted off of contaminated surfaces, like bed linens. But during the 2003 outbreak, all 35 confirmed cases in humans were caused by direct contact with the infected prairie dogs. In fact, at the time, the CDC said that “no instances of monkeypox infection were attributed exclusively to person-to-person contact.”

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The 2003 outbreak is not the only disease associated with prairie dogs. Wild populations of black-tailed prairie dogs in the American West are endemic breeding grounds for the literal plague. As in, bubonic.

Poxes and plagues? What is it that makes prairie dogs such effective vessels for such medieval-sounding diseases? As it turns out, they might not be very effective at all. Plague detected in black-tailed prairie dog towns has been the cause of multiple shutdowns in national parks such as Yosemite and other wildlife refuges in the Western U.S. in recent years. If you’ve ever visited the Badlands National Park, you may have seen yellow warning signs reminding you exactly why you should stay in your vehicle.

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But prairie dogs generally die due to plague before they have a chance to pass it onto humans; a fact sheet prepared by the Prairie Dog Coalition and the Colorado Department of Public Health and the Environment says that out of 51 total human plague cases in Colorado since 1957, only seven were linked to prairie dog exposure. (The fact sheet says, “Of those 7 cases two were related to people skinning prairie dogs, two were the result of family pets bringing home fleas after being allowed to roam freely in prairie dog colonies and three were people infected from working, playing or hiking in infected colonies.”) In modern times, prairie dogs seem to have replaced rats as plague scapegoats, but it’s more common for the fleas found in these populations to jump onto a nearby pet (such as a cat or a dog) that then brings the plague-ridden fleas home to its owners.

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However, there is another, environmental reason to fear plague found in prairie dog populations. As a keystone species, prairie dogs provide valuable services to their ecosystems, and they are an important source of food for endangered species, such as the black-footed ferret. Plague then poses a problem for these ferrets, which contract it when they hunt the prairie dogs. Fortunately, threats to the ferret population can be mitigated through the spraying of pesticides over prairie dog colonies as well as edible peanut butter vaccines such as the ones distributed by Colorado Parks and Wildlife.

For now, it seems that any vaccine to combat monkeypox cases will be distributed strategically. Unfortunately, though, it won’t involve peanut butter.

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society.

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