Monkeypox originated in animals. Could it spill back into them?

two months in With the international epidemic of monkeypox, which has so far caused nearly 6,000 infections in the United States and more than 18,000 cases worldwide, it may be old news to say this disease has visited the US before. In 2003, the virus arrived via exotic pets imported from Ghana and sickened 72 people, including children as young as 3 years old. He sent 19 people to the hospital before the outbreak died down.

Looking back, the obvious lesson seems to be how much monkeypox has changed in its behavior since then. In 2003, all cases were traced back to a person’s exposure to an infected animal. In 2022, transmission appears overwhelmingly person-to-person, attributable to sexual or skin-to-skin contact between men who have sex with men. But there is one key detail in the 2003 outbreak that worries researchers examining this new one. Two decades ago, the virus spread from captured African wildlife to American animals sold as pets. Those pets, wild prairie dogs, transmitted the virus to humans.

No one had considered such a cross-species vulnerability because human infections with monkeypox had not previously been detected outside West and Central Africa. At the time, it was well understood that African wildlife species spread the disease to people who hunted them or lived in their territories. What was surprising was that the virus could be transmitted to wildlife on other continents. It is still a warning, and it may be a warning that the virus could establish itself in new animal populations, now that it has spread to almost 80 countries.

This is by no means safe. But it is worrying enough that virologists are talking about the possibility of new host species in new territories, a spread that could constitute a “spill-over” from humans to animals, creating new exposure risks beyond what is currently known. Scientists are carefully exploring this; nobody wants to be inflammatory. “I don’t think there have been any cases at this time that are clearly due to zoonotic contagion,” says Angela Rasmussen, a virologist and associate professor at the Organization for Vaccine and Infectious Diseases Research-International Vaccine Center at the University of Saskatchewan. “And I think that would be different, because we would see cases appear without connection to an MSM sex network, and that has not happened yet.”

Because several rodent species have been found to harbor monkeypox in the countries where it was first identified, it’s a reasonable bet that several species could be vulnerable to it elsewhere. But there is not enough accumulated science to tease out the implications. Could European or American wildlife catch the disease briefly and then outgrow it? Or would it become a lingering infection between them? If it becomes endemic in wildlife populations, whether it’s prairie dogs in the countryside or rats in cities, could it spread to other species that mix with them? And how close would any of those animals have to be to people to pose an infectious risk, or to be at risk from human contact?

“What I take from the 2003 experience is that there is a wide range of species that are likely to be susceptible to monkeypox,” says Jason Kindrachuk, a microbiologist and assistant professor at the University of Manitoba who studies monkeypox and other pathogens. zoonotic. “But we still don’t fully understand what that looks like.”