Origin of monkeypox outbreak becomes clearer to scientists

Origin of monkeypox outbreak becomes clearer to scientists

When the first cases of monkeypox were identified in early May, European health authorities were puzzled. The virus was not known to spread easily among people, let alone infect dozens – and soon hundreds – of young men.

The origins of the epidemic are now becoming clearer. Genetic analysis suggests that although the monkeypox virus spreads rapidly in the open air, it has been circulating silently among humans for years.

Health officials have previously identified two versions of monkeypox in US patients, suggesting at least two separate chains of transmission. Researchers from several countries have found cases with no known source of infection, indicating undetected community spread. And a research team argued last month that monkeypox had already crossed a threshold for sustained person-to-person transmission.

The genetic information available to date noted that at some point in the last few years the virus spread better between people, said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.

“Genomic models would suggest this happened around 2018,” Dr Bedford said.

If the virus has adapted to include people as hosts, outbreaks of monkeypox could become more frequent and harder to contain. This carries the risk that monkeypox could spread from infected people to animals – most likely rodents – in countries outside Africa, which have been battling the problem for decades. The virus can persist in infected animals, sporadically triggering new infections in humans.

“We can also pass this on to animals that can spread the disease in wildlife and to humans,” said Sagan Friant, an anthropologist at Pennsylvania State University who has studied human-animal interactions in Nigeria for about 15 years. .

The longer it takes to contain the virus, the more likely it is to find a new, permanent home in people or animals, Dr. Friant said.

As of Wednesday, the United States had tallied 156 cases in 23 states and the District of Columbia. The global toll has topped 3,400 confirmed cases and another 3,500 cases are being assessed, tripling the number from two weeks ago.

In Africa, eight countries had reported more than 1,500 suspected cases and 72 deaths as of June 10, most of them in the Democratic Republic of Congo.

Monkeypox is a large double-stranded DNA virus, about seven times larger than the coronavirus. DNA-based viruses can correct their own mistakes when they replicate their genetic material. They may only collect one or two mutations per year compared to 20 to 30 mutations for an RNA virus like the coronavirus.

But the monkeypox virus appears to have accumulated a surprisingly high number of mutations – nearly 50 compared to a version that circulated in 2018, according to preliminary analyses.

Of the 47 mutations identified in one analysis, 42 carry the distinct signature of an enzyme called Apobec3. This enzyme, first discovered by researchers studying HIV, is a so-called host defense factor – an immune system weapon that animals and humans use to disarm viruses like monkeypox.

The enzyme essentially forces viruses to make mistakes when trying to replicate, which causes them to self-destruct. Mice carry only one version of this enzyme, while humans have seven. that time, Dr. Bedford said.

It is unclear how the mutations might change the virus. Of 48 mutations identified in Britain, 21 can affect the spread of the disease, its severity and its response to a treatment called tecovirimat, according to the UK Health Security Agency.

But because the mutations introduced by the Apobec3 enzyme are thought to harm the virus, their quantity alone is not worrying, said Michael Malim, a virologist at King’s College London who discovered Apobec3 in 2002. The effect of mutations is “more likely to be debilitating,” he said. Comparing the current version of the virus with samples from past years could help understand how it evolved, but such information is scarce. Nigeria did not have the capacity to sequence genetic material until 2017.

Since then, scientists there have analyzed the sequences of about 50 cases of monkeypox, according to Dr Ifedayo Adetifa, director of the Nigeria Center for Disease Control. But without the specialized equipment or expertise needed for rapid analysis, scientists have not yet finished their work, he said.

Although the researchers responded to several requests for data from outside Nigeria, Dr Adetifa said they would wait to publish their work to prevent teams with more resources from competing with them and grabbing the market. credit.

“I’m all for open data sharing and all that,” he said. “The question is, who benefits?”

Some experts have warned for years that the eradication of smallpox in 1980 left the world vulnerable to the extended family of poxviruses and increased the chances of monkeypox becoming an effective human pathogen.

In West Africa, the incidence of monkeypox has increased at least twenty-fold since 1986. In African countries in general, Dr Adetifa said, “we suspect underreporting because there has been relatively low and possibly a low perceived risk of monkeypox”. Nigeria is stepping up surveillance for monkeypox, and the number of cases could rise as more people become aware of the virus, he added.

Although monkeypox has a characteristic rash that appears on the palms of the hands and soles of the feet, it is often confused with chickenpox. Many men in the current epidemic have sores on their genitals, but these can be mistaken for sexually transmitted infections such as syphilis, gonorrhea and chlamydia.

Researchers in Italy and Germany have reported finding monkeypox DNA in semen, but it’s unclear whether the virus is spread this way or just present in semen and vaginal secretions.

The spread in young men with genital ulcers has been observed at least once before. In 2017, Nigeria recorded 228 suspected cases of monkeypox and confirmed 60. The virus spread mainly among young men who had genital ulcers.

The UK experience shows how complicated it can be to trace contacts of a virus that can be sexually transmitted, particularly in cases where infected people have had multiple anonymous partners. In an initial analysis of a subset of cases, officials said they were able to obtain the names of less than a third of the 78 reported sexual contacts.

Many cases in Africa have been attributed to contact with wild animals or the use of animal products for medicinal or cultural purposes.

As deforestation and urbanization push people and animals closer together, more viruses could make the jump to human hosts. Monkeypox is most likely to jump to people from rodents. There are approximately 2,000 species of rodents in the world, representing 40% of all mammalian species. The African rope squirrel is a prime candidate as the primary reservoir of monkeypox, but there are other contenders, including striped mice and dormice, giant pouch rats, nosed rats rusty and brush-tailed porcupines.

In a 2003 outbreak in the United States, a shipment of pouched Gambian rats imported from Africa transmitted monkeypox to prairie dogs, which then infected 71 Americans. But authorities found no signs of the virus in animals in the United States after the wave of cases ended.

There is no guarantee that luck will hold this time. “These spillovers from other species, and what that means and what the trajectory is – it’s very unpredictable,” Dr Malim said. “And it’s happening more and more.”

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