Two months into The international monkeypox epidemic, which has so far caused nearly 6,000 infections in the United States and more than 18,000 cases worldwide, may be old-fashioned to say that this disease has visited the United States before. In 2003, the virus spread via exotic pets imported from Ghana, sickening 72 people, including children as young as 3 years old. It sent 19 people to the hospital before the outbreak burned out.
Looking back, the obvious lesson seems to be how much monkeypox has changed their behavior since then. In 2003, every case could be traced back to a person’s contact with an infected animal. In 2022, transmission appears to be predominantly person-to-person, resulting from sexual or skin-to-skin contact between men having sex with other men. But there is one important detail of the 2003 eruption that is worrying researchers studying this new eruption. Two decades ago, the virus spread by migrating from captive African wild animals to American animals sold as pets. These pets, wild prairie dogs, transmitted the virus to humans.
No one had considered such a cross-species susceptibility, since human infections with monkeypox had not previously been identified outside of west and central Africa. At the time, it was common knowledge that African wildlife species passed the disease to humans who hunted them or lived in their territories. What was surprising was that the virus could be transmitted to wildlife on other continents. It remains a cautionary tale – and it could be a warning that the virus could be establishing itself in new animal populations now that it has spread to almost 80 countries.
This is by no means certain. But it’s worrying enough that virologists are talking about the possibility of new host species entering uncharted territory – a spread that could spill back from humans to animals and create new exposure risks beyond what is currently known. Scientists are studying this carefully; Nobody wants to be inflammatory. “I don’t think there have been cases at this point that are clearly related to zoonotic spillover,” said Angela Rasmussen, a virologist and associate professor at the International Vaccine Center of the University of Saskatchewan’s Vaccine and Infectious Disease Research Organization. “And I think that would be different because we would see cases unconnected to an MSM sexual network emerging, and that hasn’t happened yet.”
Since several rodent species have been found to harbor monkeypox in the countries where they were first identified, it’s a reasonable bet that several species could be susceptible to it elsewhere. But there isn’t enough accumulated science to tease out the implications. Could European or American wildlife pick up the disease briefly and then overcome it? Or would it become a persistent infection among them? If it became endemic in wildlife populations, whether it be rural prairie dogs or urban rats, could it be transmitted to other species that interbreed with them? And how close would one of these animals have to get to humans to pose a risk of infection — or to be at risk from human contact?
“What I take away from the 2003 experience is that there are a variety 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 zoonotic pathogens. “But we don’t quite understand what that looks like yet.”