Four key questions about monkeypox

Four weeks ago health authorities confirmed a case of monkeypox in the UK. Since then, more than 400 confirmed or suspected cases have appeared in at least 20 non-African countries, including Canada, Portugal, Spain and the United Kingdom, marking the largest outbreak in history outside of Africa. The situation keeps scientists on alert because the virus has appeared in separate populations in several countries, and there is no obvious relationship between many of the groups, raising the possibility of undetected local contagion.

“We have to act quickly and decisively, but there is still much to learn,” says Anne Rimoin, an epidemiologist at the University of California, Los Angeles who has studied monkeypox in the Democratic Republic of the Congo for more than a decade.

Here are some of the key questions about the recent outbreaks that researchers are racing to answer.

How did the current outbreaks start?

Since these appeared, researchers have sequenced viral genomes collected from people with monkeypox in countries including Belgium, France, Germany, Portugal and the United States. The most important piece of information they have obtained so far is that each of the sequences closely resembles that of a strain of monkeypox found in West Africa. The strain is less lethal (causing less than 1 percent mortality in poor and rural populations) than another strain that has been detected in central Africa, causing up to 10 percent mortality.

Clues have also been found about how the outbreak might have started. Although the researchers need more data to confirm their suspicions, the sequences they have analyzed so far are almost identical to each other. This suggests that a thorough epidemiological investigation would show that the recent outbreaks outside of Africa would stem from a single case.

The current sequences more closely resemble those of a handful of monkeypox cases that emerged outside of Africa in 2018 and 2019 and were linked to travel to West Africa. The simplest explanation is that this year’s first non-African case (in a person yet to be identified) was infected through contact with an animal or human carrying the virus while visiting a similar part of Africa, he says. Bernie Moss, a virologist at the US National Institute of Allergy and Infectious Diseases in Bethesda, Maryland.

But other explanations cannot be ruled out, says Gustavo Palacios, a virologist at the Icahn School of Medicine at Mount Sinai in New York. It is possible that the virus was already circulating, undetected, outside of Africa in humans or animals, and that it had been introduced during previous outbreaks. However, this hypothesis is less likely because the monkeypox virus often causes visible lesions on people’s bodies and would likely attract a doctor’s attention.

Can a genetic change in the virus explain the latest outbreaks?

Knowing if there is a genetic cause for the unprecedented spread of the virus out of Africa will be incredibly difficult, says Elliot Lefkowitz, a computational virologist at the University of Alabama who has studied the evolution of poxviruses. Researchers have not yet been able to determine precisely which genes are responsible for the greater virulence and transmissibility of the Central African strain, compared to the Western one, more than 17 years after identifying a difference between the two.

One reason for the delay is that poxvirus genomes hold many mysteries, says Lefkowitz. The genome of monkeypox is huge relative to that of many other viruses: it is more than six times larger than that of the SARS-CoV-2 coronavirus. That means they’re at least “six times harder to test,” says Rachel Roper, a virologist at Eastern Carolina University in North Carolina.

Another reason, Palacios explains, is that few resources have been devoted to genomic surveillance efforts in Africa, where monkeypox has been a public health problem for many years. So virologists don’t know anything right now, because they have few sequences to compare the sequences of new outbreaks to, he says. Funding agencies have ignored scientists who have been warning for more than a decade that new outbreaks could occur, he adds.

Ifedayo Adetifa, director of the Nigerian Center for Disease Control, says African virologists he has spoken with have expressed irritation at the difficulties they have encountered for years in obtaining funding and publishing studies on monkeypox. And now that it has spread outside the continent, public health authorities around the world seem suddenly more interested.

To understand how the virus evolves, it would also be useful to sequence the virus in animals, Palacios says. It is known to infect animals (particularly rodents such as squirrels and rats), but its natural animal reservoir has yet to be discovered in affected areas of Africa.

Can outbreaks be contained?

Since the current outbreaks began, some countries have been purchasing smallpox vaccines, which are believed to be highly effective against monkeypox, as the two viruses are related. Unlike COVID-19 vaccines, which take up to two weeks to provide full protection, smallpox vaccines are thought to protect against monkeypox if given within four days of exposure, due to the long shelf life. incubation of the virus, according to the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.

If vaccination were to be deployed, a “ring vaccination” strategy would probably be used, with inoculation of close contacts of infected persons. Andrea McCollum, an epidemiologist who leads the CDC’s poxvirus team, says the agency is not yet pursuing a ring vaccination strategy. But in the meantime, CNN is reporting that the United States plans to offer smallpox vaccines to some health professionals treating infected people. The possibility of vaccinating groups at higher risk of infection, in addition to close contacts of infected people, could also be considered, explains Rimoin.

Even if public health officials stop transmission of monkeypox in current outbreaks, virologists are also concerned about the virus spreading back to animals. Having new reservoirs of the virus in animals would increase the likelihood that it would be transmitted to people again and again, even in countries that do not harbor any known animal reservoirs of the virus. On May 23, the European Center for Disease Prevention and Control highlighted this possibility, but considered the probability “very low”. Even so, European health authorities strongly recommended that domestic rodents, such as hamsters and guinea pigs, owned by confirmed cases of monkeypox be isolated and monitored in government facilities or euthanized to avoid the possibility of contagion.

Although the risk is low, Moss says the main problem is that scientists would not know if such an infection had occurred until it was too late, because infected animals do not usually show the same visible symptoms as humans.

Is the virus spreading differently now compared to previous outbreaks?

Monkeypox virus is known to be transmitted through close contact with lesions, body fluids, and respiratory droplets from infected people or animals. However, health authorities have examined sexual activity at two parties raves of Spain and Belgium as engines of the transmission of the disease, according to the Associated Press, which leads to speculation that the virus has evolved and is better adapted to sexual transmission.

However, cases linked to sexual activity do not mean that the virus is more contagious or sexually transmitted, but rather that it spreads easily through close contact, says Rimoin. Unlike SARS-CoV-2, which is not thought to last long on surfaces, poxviruses can survive for a long time outside the body, making surfaces such as bed sheets and doorknobs a potential vector of infection. spread, says Roper.

Although health authorities have pointed out that there have been numerous cases in men who have homosexual relationships, Rimoin stresses that the most likely explanation for the spread of the virus among them is that the virus was accidentally introduced into the community, and that it has continued to spread there. .

According to McCollum, all the attention given to monkeypox has highlighted how much scientists still have to unravel about the virus. “When all this has settled down, we will have to think long and hard about what the research priorities should be,” he concludes.

Max Kozlova

Article translated and adapted by Research and Science with the permission of Nature Research Group.

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