Squirrels could make monkeypox an eternal problem

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In the summer of 2003, just weeks after an outbreak of monkeypox sickened about 70 people in the Midwest, Mark Slifka visited “the superspreader,” he told me. , “which infected half of Wisconsin’s cases”.

Chewy, a prairie dog, had then succumbed to the disease, which he had almost certainly caught in an exotic animal facility he had shared with infected rats in Ghana. But his owners’ other prairie dog, Monkey – named after the way he climbed into his cage – had contracted the pathogen and survived. “I was a little worried,” said Slifka, an immunologist at Oregon Health & Science University. All of the traits that made Monkey a charismatic pet also made him a contagious threat. He cuddled and nibbled his masters; when they left the house, he swaddled himself in their clothes until they returned. “That was cute,” Slifka told me. “But I was like, ‘Can Monkey be in his cage when we come?'”

Slifka made it home without smallpox, and the 2003 outbreak died out. But this outbreak of cases was a close call: an opportunity for the virus to take hold in a new animal host. A lasting interspecies leap, similar to the one SARS-CoV-2 turned into a white-tailed deer, and monkeypox will be “with us forever” in the United States, says Barbara Han, disease ecologist at the Cary Institute, At New York. In central and western Africa, where the virus is endemic, scientists suspect that at least two species of rodents intermittently transmit it to humans. And as the largest outbreak of monkeypox outside of Africa in history continues to spread – more than 2,700 confirmed and suspected cases have been reported in around three dozen countries – the virus is now receiving many more shots. to goal. This time we may not be so lucky; the geography of monkeypox may soon change.

Any new jump could reshape the future of this virus, and for us. Experts consider that possibility unlikely — “low risk, but it’s a risk,” says CDC disease ecologist Jeffrey Doty. Existing animal reservoirs make some diseases almost impossible to eradicate; the emergence of new ones could sow future epidemics in places where they are not currently common. If researchers can identify some of these animals and keep them from intermingling with us, we might avoid some of these problems. But it’s a big if. With so many susceptible animals, figuring out which ones harbor the virus could send researchers on a year-long race, with no clear finish line.


Scientists first discovered monkeypox in the 1950s, in two species of monkeys housed in a Danish pet store; hence the name, which will probably change soon. But in the decades that followed, the best evidence for the persistence of the virus in animals came from rodents in central and western Africa, including rope squirrels, sun squirrels, Gambian pouch rats and dormice. All signs point to rodents being “responsible for keeping this virus in the wild,” Doty told me, and so he and his colleagues worry about these mammals the most when considering which animals in the regions non-endemic may pose the most future risk.

But one plot rodents roam the planet – about 2,500 species, which together make up about 40% of known mammals. Although not all species are capable of carrying monkeypox – for example, guinea pigs, golden hamsters, and house mice and rats generally are not – many of them can.

Building an animal tank’s case typically requires years of fieldwork, rigorous safety protocols, and a lot of luck. For a few viruses, the reservoir narrative is relatively clear: Hendra virus, an often fatal respiratory infection, typically travels from bats to horses and then to humans; most hantaviruses, which can cause life-threatening fevers, take up residence in one species of rodent each. Monkeypox, however, is much less picky than that. Experts suspect that several animals allow the virus to percolate in nature. How much, however, is anyone’s guess.

The gold standard for establishing a reservoir requires isolation of active virus, proof that the pathogen was xeroxing inside a viable host. But in the wild, “you can break your back and end up having only five animals of a species,” Han, who uses machine learning to try to predict potential monkeypox reservoirs, told me. “And what are five animals? They may be free of the virus in question, even if other members of their population harbor it; they may have been caught at an age or during a season when the pathogen is not present. And among animals that harbor the virus, a reservoir may not always be the most obvious species: rodents might be among the most commonly detected carriers of monkeypox, but outbreaks in zoos and experiments in laboratory showed that the virus was able to infiltrate anteaters, rabbits, and a handful of primates, as well as other mammals without mice. In several of these and other species, scientists have found antibodies that recognize poxviruses, hinting at past exposures; they even discovered the DNA of the virus. Only twice, however, has anyone found an active virus in wild animals: a rope squirrel from the Democratic Republic of Congo in the 1980s and a sooty mangabey, found in Ivory Coast a decade ago. ‘years.

Even those instances weren’t slam dunks. It takes more to “determine which is a reservoir, versus which ones are infected, but aren’t actually responsible for keeping the virus circulating in people,” environmental ecologist Jamie Lloyd-Smith told me. diseases at UCLA. Just because an animal could transmit the virus to us doesn’t mean it will.


For this to happen, humans must have enough contact with animals to make exposure likely – during routine bushmeat hunts, for example, or in fractured landscapes where animals forage in and around people’s houses. Lloyd-Smith, who surveyed people in the Congo, said analyzing what’s risky and what’s not is harder than it looks: most people he talks to interact time with forest creatures. “It’s not like, ‘Oh, these are the people who ate the salmon mousse at church breakfast,'” he told me. To complicate matters further, wild and domestic animals can act as intermediaries between humans and a real reservoir, says Stephanie Seifert, a disease ecologist at Washington State University. Researchers sometimes have to traverse webs of interaction, moving through degrees of separation a la Kevin Bacon, to identify the original source.

Uncovering these natural origins is key to preventing the virus from moving to new real estate and, possibly, breaking existing leases. In West and Central Africa, for example, where some people’s livelihoods depend on hunting and eating wild game, “you can’t just say, ‘Don’t interact with the rodents,'” Seifert said. But with further investigation, says Clement Meseko, a veterinarian and virologist who studies the human-wildlife interface at the National Veterinary Research Institute of Nigeria, perhaps experts could eventually identify a few species and then recommend sustainable alternatives. in their place. Improved sanitation to keep rodents away from humans could also help. The same goes for the distribution of vaccines to people who live in high-risk regions of endemic countries – or perhaps to worrisome wild animals themselves. (Vaccinating animals is a pretty noble goal, but can still be a better alternative to slaughtering animals, which “often doesn’t work,” Lloyd-Smith said.)

In the United States, amid the current outbreak of monkeypox cases, the CDC has recommended that infected people completely avoid interacting with pets, livestock, and other animals. Although no cats or dogs have ever had the infection, “we don’t know anything about monkeypox in common pets,” Doty said. For now, it’s best to play it safe.

And the most significant way to prevent the virus from spreading into a new animal species, Han said, “is to control the human outbreak.” Already, the range of monkeypox species is formidable, and in today’s world, humans and animals collide more frequently. Amid the ongoing outbreak, Meseko, who is spending the year completing a fellowship in St. Paul, Minnesota, took note of “how squirrels are just free everywhere.” Whatever threat they might pose to us, “animals are also endangered by humans,” he told me.

Human activity, after all, brought monkeypox to the United States in 2003 and a coterie of prairie dogs that included Chewy and Monkey. “They wouldn’t have been geographically exposed without us moving around this virus,” Seifert said. And the human desire for pets has brought these prairie dogs to dozens of homes across the Midwest. People mobilize disease; our species also poses a huge infectious threat to the planet. The current outbreak of monkeypox, for example, is more sprawling and human-centric than those documented in the past. And the more opportunities the virus has to infiltrate new hosts, the more opportunities it has to expand its species range. Any runoff into the animals might not be detected until too late; perhaps, some experts pointed out, this already happened a long time ago, sowing a reservoir that helped the ongoing epidemic break out. “We don’t have any evidence of this at this time,” says Grant McFadden, a poxvirus expert at Arizona State University. “But that could change in no time.”

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