The Virus That Causes Mpox Keeps Getting Better at Spreading in People

The virus that causes mpox continues to improve and spread in people

Who Max Kozlov & Nature magazine

Another strain of the virus that causes mpox can spread easily from person to person, according to a study of the pathogen’s genome. This development could be further complicated efforts to stop the spread of the disease In Central Africa, which has seen an increase in infections in the last year. And what is driving this rise today has left researchers scratching their heads.

The findings suggest that the strain, called clade Ia, is spreading persistently between people—perhaps through sexual contact—in an outbreak in Kinshasa, the capital of the Democratic Republic of Congo (DRC). Previously, the viral variant was known to be primarily transmitted from animals to humans in Central Africa.

“We know that viruses evolve: we saw it with Ebola, we saw it with COVID and we expected to see it with mpoxa,” says Placide Mbala, head of epidemiology and global health at the National Institute for Biomedical Research. Kinshasa, who led the analysis. “We don’t know how far these adaptations can go, and we are collecting data to understand how this evolution is taking place.”

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The first results, which have not yet been peer-reviewed, were Posted on October 22 Virological genomic-epidemiology discussion forum.

Mpox diversifies

Four variants of monkeypox virus are known: clades Ia, Ib, IIa and IIb (see ‘Quick guide to monkeypox virus strains’). Historically, clade I viruses have appeared mostly in Central Africa, and clade II viruses in West Africa.

This all changed in the mid-2010s, when a clade II strain sparked an outbreak in Nigeria. At that time, some researchers proposed that the variant may be able to be transmitted through sexual intercourse. Their insights were illuminating: a similar clade called IIb, IIb, In 2022 mpox sparked a global outbreak which has infected more than 90,000 people and continues to this day.

Meanwhile, clade I viruses have caused sporadic infections in humans for more than 50 years, especially in rural regions of Central Africa. But at the end of 2023, researchers identified a rapidly growing outbreak Urban areas in densely populated eastern regions of the DRC disproportionately affected sex workers, suggesting that this virus strain, like IIb, could easily spread between people.

Genomic sequencing confirmed that the variant causing this outbreak had several key differences from clade I viruses, which the researchers named Ib. This tension It has been detected in the UK, Sweden, Thailand, India, Germany and six African countries that had previously not reported mpox infections. The DRC has been particularly hard hit: the country has reported nearly 36,000 suspected infections and more than 1,000 deaths from mpox in 2024.

But now, about a year after researchers detected a clade Ib outbreak in eastern DRC, clade Ia is also a concern for health officials. Tension has also risen in the western regions of the DR and in Kinshasa. In fact, the circulation of Ia and Ib in the capital threatens the 17 million people who live there and raises the possibility of the international spread of clade I, considering that Kinshasa is a travel hub.

Quick Guide to Monkeypox Virus Strains

• Clade Ia: The strain has been spreading in Central Africa since the virus was discovered infecting humans in 1970. Most of the infections have been in children, and it was known that it was mainly transmitted from animals to humans – until recently.

• Clade Ib: A strain that has caused a surge in cases in Central Africa since its discovery in late 2023. It is known to spread from person to person, even through sexual intercourse.

• Clade II: the least studied mpox strain. It has spread mainly in Guinea, Liberia and Ivory Coast. Modes of transmission are not fully understood; there is no documented evidence of sexual transmission, but close contact is likely to contribute to the spread of all.

• Clade IIb: the still simmering tension of the 2022 global outbreak. It is known to spread from person to person, including through sexual contact. The most affected population has been men who have sex with men.

Signs of evolution

Health officials are using genomic sequencing tools to track the outbreak. As part of the effort, Mbala and his colleagues sequenced virus samples from infections in Kinshasa. In the clade Ia and Ib virus samples, they found a specific pattern of single-letter genetic mutations indicative of the ongoing battle between the human immune system and the virus, a pattern that would be unlikely to appear in the absence of a persistent human system. extension to man.

However, the pattern did not appear in a report posted on a preprint server in August. In that study, a team sequenced clade Ia virus samples collected between 2018 and 2024. The researchers’ failure to spot the pattern suggests it may be a recent development. “We didn’t get strong indications of evolution” in the more rural and endemic regions of the DRC, says Jason Kindrachuk, a virologist at the University of Manitoba in Winnipeg, Canada, who collaborates with Mbala and is an August co-author. preprint as well as Virological. “But in Kinshasa, something special seems to be happening.”

Clade Ia may also have the ability to spread sexually: the first case of sexually transmitted clade I mpox was reported last year, and another publication is forthcoming, Kindrachu says.

Given that clade I has been circulating among animals and people in the DRC since the 1970s, Kindrachuk added that it will be important to investigate why clade Ib suddenly emerged in 2023, and why Ia has caused the increase in the number of infections detected in the past. two years “Because we are better at surveillance or because we are more aware of mpox at the community level? Is it because people have moved more after the (COVID-19) pandemic or because they have become more confident in contact with wildlife? he asks.

For now, plans to roll out the continent’s first doses of mpox vaccines are unlikely to change in light of these findings, says Nicaise Ndembi, a virologist at the African Centers for Disease Control and Prevention in Addis Ababa. Health officials have already allocated doses to regions with higher numbers of infections, regardless of the specific strain found in the area, he says.

This article is and was reproduced with permission first published On October 30, 2024.