Monkeypox is a zoonosis. That is, a disease that is transmitted from some animals to humans. Evidence of infection by this virus has been found in animals such as squirrels, Gambian rats, dormouse and different species of monkeys on the African continent. But with the outbreak in 29 countries where the pathology was not endemic, like the one that is happening in the world this year, there is a risk that the smallpox virus will lead to a “reverse zoonosis”: that affected humans will transmit the infection to other animals that live nearby. As a consequence, there would be a reservoir of the virus in domestic and wild animals outside of Africa.
The current outbreak can be considered historic, as it affected the most people outside of Africa: 1226 cases on multiple continents. Many of the cases are men who have sex with menalthough from the World Health Organization and UNAIDS it was clarified that the infection can be acquired by anyone, regardless of their gender identity and sexual orientation.
The first time monkeypox cases were reported outside of Africa was in the United States in 2003. According to the Centers for Disease Control and Prevention (CDC) there were 47 confirmed and probable cases of monkeypox reported in six states: Illinois, Indiana, Kansas, Missouri, Ohio and Wisconsin. All of the people infected with monkeypox in this outbreak became ill after contact with pet prairie dogs. The pets became infected after being housed near small mammals imported from Ghana.
The increase in cases in all 29 countries has raised the possibility that the monkeypox virus could become permanently established in wildlife outside of Africa.. In this way a reservoir could be formed that could give rise to repeated human outbreaks.
There are currently no detected animal reservoirs outside of Africa, but the 2003 outbreak in the United States came close, some scientists suspect, largely because nearly 300 of Ghana’s animals and dogs from the exposed prairie. “We narrowly escaped monkeypox becoming established in a population of wild animals” in North America, he told the magazine. Science Anne Rimoin, an epidemiologist at the University of California, Los Angeles, who has long studied the disease in the Democratic Republic of the Congo (DRC). In the end, however, studies of wild animals in Wisconsin and Illinois never found monkeypox virus, none of the infected humans spread the disease to other people, and concerns about that outbreak evaporated.
Viruses often do like a ping-pong between humans and other species. Although COVID-19 disease is generally believed to be the result of the coronavirus jumping from a bat or other host to people, humans, in “reverse zoonosis,” have also infected white-tailed deer with the virus. minks, cats and dogs. In an Ohio study, coronavirus antibodies were found in more than a third of 360 wild deer sampled. In centuries past, when humans carried plague and yellow fever to new continents, those pathogens created reservoirs in rodents and monkeys, respectively, which then re-infected humans.
As the current monkeypox outbreak spreads, the virus has an unprecedented opportunity to establish itself in non-African animal species, which could infect humans and provide a greater opportunity for more dangerous variants to evolve. “Monkeypox reservoirs in wildlife outside of Africa is a scary scenario,” said Bertram Jacobs, a virologist at Arizona State University (ASU) in Tempe.
Health authorities in several countries have advised people with monkeypox lesions to avoid contact with their pets until they heal. For example, the health authorities of the United Kingdom published a guide for the care of patients, in which they recommended that they should not be near their pets. About 80% of the cases have been in Europe, and the European Food Safety Authority said that as of May 24, no domestic or wild animals had been infected. But he added that “Close collaboration between human and veterinary public health authorities is necessary to manage exposed pets and prevent the disease from spreading to wildlife.”
The possibility that humans infected with the monkeypox virus will transmit it to wildlife outside of Africa “justifies serious concern,” said William Karesh, a veterinarian with the EcoHealth Alliance. who spoke of this possibility last week at a consultation on monkeypox research organized by the World Health Organisation. For now, the limited number of human cases reduces the chances. But domestic rodents are of particular concern, as are the large numbers of wild animals – accounting for 40% of all mammals – that frequently raid garbage and could be infected by contaminated waste.
Studies have not yet been able to determine the African reservoir of the monkeypox virus. Although a laboratory in Copenhagen, Denmark, first identified it in research monkeys in Asia in 1958, scientists now believe that the primates were infected from a source in Africa. All human cases since the first recorded in 1970, in the Democratic Republic of the Congo (then Zaire), could be related to the spread of the virus from animals in Africa.
However, to dateOnly six wild animals trapped in Africa have detected the virus: three chipmunks, a Gambian rat, a shrew and a mangabey monkey. Antibodies against monkeypox virus are more abundant in African squirrels. “We still don’t fully understand the current reservoir, other than that it’s rodents”Grant McFadden admitted., virologist at Arizona State University, in the United States. But it is clear that monkeypox can infect many other types of animals in the wild and in captivity.
A 1964 outbreak at a zoo in Rotterdam, the Netherlands, sickened giant anteaters, orangutans, gorillas, chimpanzees, a gibbon and a marmoset. Researchers have intentionally infected many laboratory animals, including rabbits, hamsters, guinea pigs, and chickens, although the virus does not cause disease in several of them.
For many viruses, the relationship between viral surface proteins and receptors on host cells determines which animals they can infect. The coronavirus Spike protein, for example, latches onto angiotensin-converting enzyme 2, a protein found on a variety of cells in humans, mink, cats, and many other species. But poxviruses – such as monkeypox or human smallpox – do not appear to require host-specific receptors, allowing many to infect a wide range of mammalian cells.
Vaccinia, the smallpox vaccine virus, can even infect fruit flies as well as cows and people, recalled David Evans, a poxvirus researcher at the University of Alberta, Edmonton. Bernard Moss, a virologist at the National Institute of Allergy and Infectious Diseases (NIAID) in the United States, commented that some poxviruses have proteins on their surface that form a “hydrophobic face”, an area that repels water and that can bind nonspecifically to hydrophilic cell membranes and initiate the infection process.
But whether a poxvirus can copy itself, and ultimately persist in a species to create a reservoir, depends on how well it fends off host immune attacks. Poxviruses have a relatively large complement of genes, some 200, with about half undermining the host’s immune response. Some viruses run and hide or are stealthy, avoiding direct contact with elements of the immune system. Instead, poxviruses fight back.
Their defense against host immunity appears to be largely dependent on a family of genes scattered throughout their genomes that encode little-known proteins containing domains known as ankyrin repeats.. The poxvirus proteins that contain these repeats act like “molecular flypaper,” Dr. Evans said, attaching themselves to host proteins that are involved in coordinating the immune response. “Orthopoxviruses have these sets of ankyrin repeats, and for the most part we don’t really know what they’re targeting,” Evans added. “But the bottom line is that they are probably the key to trying to understand why some of these viruses have the host range that they do.”
Variola, the smallpox virus, appears to have lost many of those immune-evasion genes.. It only persists in humans and has no animal reservoir, so the global vaccination campaign was able to eradicate it. Monkeypox is clearly more promiscuous. But the many questions that remain about it mean that it is not known whether it will create reservoirs in non-African wildlife. “One of the challenges has been the lack of interest,” said Lisa Hensley, a microbiologist with the US Department of Agriculture. that she began researching monkeypox in 2001 as part of a US Army laboratory.
Dr Hensley, who has worked on monkeypox for nearly a decade and collaborated with Rimoin, urged people to keep an open mind about how the virus behaves and what it might do in the future. “We’re acknowledging that this is a disease that we need to be concerned about and that we really don’t know as much as we think we do,” he said.