Origin of monkeypox outbreak becomes clearer for scientists

When the first monkeypox cases were identified in early May, European health officials were stumped. It is known that the virus cannot easily spread among people, let alone infect dozens, and soon hundreds of young people.

The origin of the outbreak is now becoming clearer. Genetic analysis shows that although the monkeypox virus spreads rapidly in the open air, it circulates unnoticed among humans for years.

Health officials have already identified two versions of monkeypox among American patients, suggesting at least two separate chains of transmission. Investigators in several countries found cases with no known source of infection, indicating unnoticed community spread. And one research team last month argued that monkeypox is already crossed the threshold into sustained human-to-human transmission.

Genetic Information available so far indicated that at some point in the past few years the virus has gotten better at spreading between people, said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.

“Genomic patterns suggest that this happened around 2018,” says the doctor. Bedford said.

If the virus adapts to include humans as hosts, monkeypox outbreaks could become more frequent and harder to contain. This carries the risk that monkeypox could be transmitted from infected humans to animals – most likely rodents – in countries outside of Africa, which has struggled with the problem for decades. The virus can persist in infected animals, causing sporadically new infections in humans.

“We can also pass it back to animals that can spread the disease in the wild, and back to humans,” said Sagan Fryant, an anthropologist at Pennsylvania State University who has been studying human-animal interactions in Nigeria for about 15 years.

The longer it takes for the virus to be contained, the more likely it is to find a permanent new home in humans or animals, the doctor says. Frian said.

As of Wednesday, 156 cases have been identified in the US across 23 states and the District of Columbia. The global toll has surpassed 3,400 confirmed cases, and another 3,500 cases are estimated, three times more than two weeks ago.

Africa has eight countries informed over 1,500 suspected cases and 72 deaths as of June 10, most of which were in the Democratic Republic of the 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 replicating their genetic material. They can only harvest one or two mutations per year, compared to 20 to 30 mutations for an RNA virus like the coronavirus.

But the monkeypox virus seems to have accumulated an unexpectedly large number of mutations – almost 50 compared to the 2018 version. preliminary analyzes.

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 neutralize viruses such as monkeypox.

The enzyme essentially causes viruses to make mistakes when they try to reproduce, causing them to self-destruct. Mice carry only one version of this enzyme, while humans have seven. The rapid accumulation of mutations that has characterized the enzyme since 2018 suggests that monkeypox may have passed to humans as carriers around the same time. Bedford said.

It is not yet clear how mutations can change the virus. Out of 48 mutations identified in the UK21 can affect the spread of the disease, its severity and how well it responds to a treatment called tecovirimat, according to the UK Health Security Agency.

But since the mutations introduced by the Apobec3 enzyme are designed to harm the virus, their numbers are not in themselves a concern, said Michael Malim, the King’s College London virologist who discovered Apobec3 in 2002. , “He said. Comparing the current version of the virus with samples from the past few years can help understand how it evolved, but this information is not enough. Nigeria was not able to sequence the genetic material until 2017.

Since then, scientists have analyzed the sequences of about 50 cases of monkeypox, according to Dr. K. Ifedayo Adetif, director of the Nigerian Center for Disease Control. But without the special equipment or expertise required for rapid analysis, the scientists have not yet completed their work, he said.

Although the researchers sent several requests for data from outside Nigeria, Dr. Adetifa said they would wait to publish their work to prevent teams with more resources from out-competing them and gaining recognition.

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

Some experts warned for years that the eradication of smallpox in 1980 left the world vulnerable to the wider poxvirus family and increased the likelihood of monkeypox becoming a successful human pathogen.

In West Africa, the incidence of monkeypox has risen at least twenty times since 1986.. In African countries in general, Dr. Adetifa said: “We suspect some underreporting because there was relatively low awareness and possibly a low perceived risk of monkeypox.” He added that Nigeria is stepping up surveillance of monkeypox and the number of cases could rise as more people become aware of the virus.

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 outbreak have lesions on their genitals, but these can be mistaken for sexually transmitted infections such as syphilis. gonorrhea and chlamydia.

Researchers in Italy and Germany announced the discovery of monkeypox DNA in semenbut it is not clear if the virus is spread in this way or is simply present in semen and vaginal secretions.

Spread among young men with genital ulcers has been observed at least once before. In 2017, Nigeria reported 228 suspected cases of monkeypox and 60 confirmed cases. Spread of the virus especially among young people who had ulcers on the genitals.

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

Many cases in Africa are associated with contact with wild animals or the use of animal products for drug or cultural practices.

As deforestation and urbanization push people and animals into close quarters, more viruses can enter humans. Monkeypox is most commonly transmitted to humans by rodents. There are about 2,000 species of rodents in the world, representing 40 percent of all mammalian species. The African rope squirrel is a leading candidate as the main reservoir of monkeypox, but there are other contenders, including striped mice and dormice, giant marsupial rats, rusty-nosed rats and brush-tailed porcupines.

During an outbreak in 2003 in the United States, a shipment of Gambian pouch rats imported from Africa transmitted monkeypox to prairie dogs, which then infected 71 Americans. But officials found no signs of the virus in animals in the United States after the tide of cases stopped.

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