Smallpox could open a new reservoir in the animal kingdom – health

In May 2003, eleven days after being bitten by one of her prairie dogs, a three-year-old Wisconsin girl became the first person outside Africa to become infected with chickenpox. Two months later, her parents and 69 other people in the United States suspected or confirmed cases of such an infection. The smallpox virus is endemic in some parts of Africa, and rodents imported from Ghana apparently infected captured prairie dogs from North America when they were housed together by an animal dealer in Texas.

At that 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 on different continents, many of whom are men who have sex with men. The size of the outbreak also opened up the opportunity scientists were afraid of: the smallpox virus could settle permanently in wildlife outside Africa and create a reservoir that could lead to repeated outbreaks among humans.

There is currently no known animal reservoir outside of Africa. But the outbreak in 2003 was already close – mainly because almost 300 animals from Ghana and abandoned prairie dogs were never found. “We narrowly missed the fact that smallpox has settled in the wildlife population in North America,” said Anne Rimoin, an epidemiologist at the University of California, Los Angeles, who is studying the disease in the Democratic Republic of the Congo (DRC).

However, wildlife surveys in Wisconsin and Illinois have never found the monkeypox virus, none of those infected have spread the disease to other people, and fears of this exotic outbreak are long gone. Will the world be so lucky this time?

Giant ants, orangutans and chimpanzees fell ill in 1964 at the Rotterdam Zoo

Viruses often jump back and forth between humans and other species. Although it is widely believed that Sars-CoV-2 jumped from bat to human through another host, humans also infected the coronavirus with white-tailed deer, mink, cats, and dogs in “reverse zoonoses.” In the Ohio study, anti-Sars-CoV-2 antibodies were found in more than a third of the 360 ​​wild animals studied. And in past centuries, when humans brought plague and yellow fever to new continents, these pathogens formed reservoirs in the original rodents or monkeys, which later re-infected humans.

Virology: Color electron micrograph of monkeypox virus.

Color electron micrograph of monkeypox virus.

(Photo: Andrea Männel / dpa)

As the smallpox epidemic spreads around the world, the virus has an unprecedented opportunity to gain a foothold in non-African species. From there, the pathogen could switch back to humans and have more and more opportunities to develop new, perhaps more dangerous, variants. “Monkey pox tanks in wildlife outside Africa are a scary scenario,” said Bertram Jacobs, a virologist at Arizona State University in Tempe.

Health authorities in several countries have advised people with chickenpox lesions to avoid contact with their pets. About 80 percent of cases have so far occurred in Europe, and the European Food Safety Authority said no domestic or wild animals were infected by 24 May. However, the agency added that “close cooperation between human and veterinary experts is needed to treat exposed pets and prevent the transmission of the disease to wild animals”.

The possibility that people infected with the smallpox virus could transmit the virus to wildlife outside Africa “raises serious concerns,” said William Karesh, a veterinarian at the EcoHealth Alliance. For now, Karesh said the chances are still low due to the limited number of cases in humans. Of particular concern, however, were the rodents kept as pets, as well as large numbers of wild rodents, which often dig up waste and could become infected with contaminated waste.

The African monkey pox virus reservoir has yet to be 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 satisfied mangabey monkey. Antibodies to the monkeypox virus are most common in African squirrels. “We still don’t know much about the current reservoir other than rodents,” said Grant McFadden, a pox virus researcher at Arizona State University.

“Smallpox viruses, in general, stand up and fight.”

However, it is clear that smallpox can infect many other species in the wild and in captivity. In 1964, giant ants, orangutans, gorillas, chimpanzees, gibbons and marmosets erupted at the Rotterdam Zoo. The researchers deliberately infected laboratory animals such as rabbits, hamsters, guinea pigs and chickens.

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

However, whether a poxvirus can thrive in an infected cell and possibly survive in a species to form a reservoir depends on how well it can repel 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. “Smallpox viruses, in general, stand up and fight.”

Variola, a smallpox virus, has apparently lost many of these genes that affect the immune system. It survives only in humans and has no reservoir in animals, which is why it was eradicated by a worldwide vaccination campaign. Monkey pox is clearly more promiscuous. However, it is not yet known whether it is able to form reservoirs in non-African wildlife. “One of the problems is lack of interest,” said Lisa Hensley, a U.S. Department of Agriculture microbiologist who began studying smallpox in a U.S. military lab in 2001.

Hensley, who has spent nearly a decade researching smallpox at the National Institute of Allergies and Infectious Diseases (NIAID) and worked with Anne Rimoin, urges people to stay alert and watch the virus behave and what it can do next. “We realize it’s a worrying disease and we don’t know as much as we think we know.”

This post is in the original in a scientific journal Science he appearedissued by AAAS. German editorial staff: cvei

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