Monkeypox could open a new reservoir in the animal kingdom

In May 2003, eleven days after being bitten by one of her prairie dogs, a three-year-old girl from Wisconsin became the first person outside of Africa to contract monkeypox. Two months later, his parents and 69 other people in the United States had suspected or confirmed cases of such an infection. The monkeypox virus is endemic in parts of Africa and rodents imported from Ghana had apparently infected captive prairie dogs from North America when a pet dealer in Texas took them in together.

At this time, the pathogen was quickly stopped. The situation is different in the current epidemic. It affects more people outside Africa than ever before – more than 2,600 cases across multiple continents, many of them men who have sex with men. The size of the outbreak has also opened up an opportunity that has researchers cringing: the monkeypox virus could become permanently established in wildlife outside of Africa, creating a reservoir that could lead to repeated epidemics in humans.

There are currently no known animal reservoirs outside of Africa. But the 2003 outbreak was already a close affair – mainly because nearly 300 of Ghana’s animals and abandoned prairie dogs were never found. “We just missed establishing monkeypox in a wild animal population in North America,” said Anne Rimoin, an epidemiologist at the University of California, Los Angeles, who studies the disease in the Democratic Republic. of the Congo (DRC).

However, wildlife surveys in Wisconsin and Illinois never found the monkeypox virus, none of those infected transmitted the disease to others, and concerns about this exotic outbreak have since subsided. long time. Will the world be so lucky this time?

Giant anteaters, orangutans and chimpanzees fell ill in a 1964 outbreak at a Rotterdam zoo

Viruses often move back and forth between humans and other species. Although it is widely believed that Sars-CoV-2 jumped from a bat to humans via another host, humans have also infected white-tailed deer, mink, cats and dogs with the coronavirus in “reverse zoonoses”. In a study conducted in Ohio, antibodies against Sars-CoV-2 were found in more than a third of 360 wild animals examined. And in centuries past, as humans brought plague and yellow fever to new continents, these pathogens formed reservoirs in rodents or native monkeys, which later infect humans again.

As the monkeypox epidemic spreads worldwide, the virus has an unprecedented opportunity to establish itself in non-African animal species. From there, the pathogen could return to humans and have more and more opportunities to develop new, possibly more dangerous variants. “Reservoirs of monkeypox in wildlife outside of Africa are a frightening scenario,” said Bertram Jacobs, a virologist at Arizona State University in Tempe.

Health authorities in several countries have recommended that people with monkeypox lesions avoid contact with their pets. So far around 80% of cases have been in Europe and the European Food Safety Authority said no domestic or wild animals had been infected as of May 24. However, the agency added that “close collaboration between human and veterinary professionals is necessary to treat exposed pets and prevent disease transmission to wild animals.”

The possibility that humans infected with the monkeypox virus could transmit it to wild animals outside of Africa “raises serious concerns,” says William Karesh, a veterinarian at the EcoHealth Alliance. For now, Karesh said the chances were still low due to the limited number of human cases. However, rodents kept as pets were of particular concern, as well as the large number of wild rodents, which often scavenge and can become infected from contaminated waste.

The African reservoir of the monkeypox virus has not yet been precisely determined. So far, the virus has only been detected in six wild animals captured in Africa: three rope squirrels, a Gambian rat, a shrew and a sooty mangabey monkey. Antibodies to monkeypox virus are most commonly found in African squirrels. “We still don’t know much about the current reservoir other than rodents,” says Grant McFadden, a smallpox virus researcher also at Arizona State University.

“The smallpox viruses, as a whole, stand up and fight.”

However, it is clear that monkeypox can also infect many other animal species in the wild and in captivity. A 1964 outbreak at a Rotterdam zoo killed giant anteaters, orangutans, gorillas, chimpanzees, a gibbon and a marmoset. Researchers have intentionally infected laboratory animals such as rabbits, hamsters, guinea pigs and chickens.

In many viruses, the surface proteins that can couple to host cell receptors determine which animals the pathogen can infect; the spike protein of Sars-CoV-2, for example, binds to the ACE2 protein, which is found on a variety of cells in humans, mink, cats and many other species. However, poxviruses do not appear to require specific host receptors, allowing many to infect a wide range of mammalian cells. David Evans, a smallpox virus researcher at the University of Alberta in Edmonton, notes that vaccinia, the smallpox vaccine virus, can infect fruit flies in addition to cows and humans.

However, whether a poxvirus can thrive in an infected cell and ultimately survive in a species to form a reservoir depends on its ability to fend off host immune attacks. Compared to other pathogens, smallpox has many genes – about 200 – and about half of them subvert the host’s immune response. “Some viruses hide and avoid direct contact with the immune system,” says McFadden. “The smallpox viruses, as a whole, stand up and fight.”

Smallpox, the pox virus, seems to have lost many of these genes that affect the immune system. It only survives in humans and has no reservoir in animals, which is why the global vaccination campaign has eradicated it. Monkeypox is clearly more promiscuous. But it is not yet known whether it is able to create reservoirs in non-African fauna. “One of the problems is lack of interest,” says Lisa Hensley, a US Department of Agriculture microbiologist who began her research on monkeypox in a US Army lab in 2001.

Hensley, who spent nearly a decade researching monkeypox at the US National Institute of Allergy and Infectious Diseases (NIAID) and collaborated with Anne Rimoin, urges people to remain vigilant and watch the behavior of the virus and what it might do next. “We realize this is a worrying disease and we don’t know as much about it as we think we know.”

This post is in the original science magazine Science appeared, published by the AAAS. German edition: cvei