The virus that causes Mpox continues to spread among the population

The virus that causes Mpox continues to spread among the population

Max Kozlov & Nature Magazine

Additional strains of the virus that cause mpox may be easily transmitted from person to person, according to analysis of the pathogen’s genome. The development could further complicate efforts to contain the spread in Central Africa, where cases have soared over the past year. And researchers are puzzled over what’s causing this current surge.

The findings suggest that the strain, called clade Ia, is spreading persistently among people, possibly through sexual contact, in an outbreak in Kinshasa, the capital of the Democratic Republic of Congo (DRC). . Until now, this virus variant was known to be transmitted primarily from animals to humans in Central Africa.

“We know that viruses evolve. We’ve seen it with Ebola, we’ve seen it with COVID-19, and we expected it to evolve similarly with mpox,” said the National Institute of Biomedical Research. Placido Mbala, Director of Epidemiology and Global Health. Kinshasa co-led the analysis. “We don’t know how far these adaptations will go, but we are collecting data to understand how this evolution is occurring.”

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The preliminary results, which have not yet been peer-reviewed, were posted on the genomic epidemiology discussion forum Virological on October 22.

Diversification of Mpox

There are four known variants of monkeypox virus: clades Ia, Ib, IIa, and IIb (see Quick Guide to Monkeypox Virus Strains). Historically, clade I viruses emerged primarily in central Africa and clade II viruses in west Africa.

This all changed in the mid-2010s. Because clade II strains caused an outbreak in Nigeria. At the time, some researchers suggested the variant could be transmitted through sexual contact. Their insights proved prescient. A similar clade II strain, called IIb, caused an mpox pandemic in 2022 that infected more than 90,000 people and is still ongoing.

On the other hand, clade I viruses have been causing sporadic infections in people, mainly in rural areas of Central Africa, for more than 50 years. However, in late 2023, researchers identified that infections were spreading rapidly in densely populated urban areas in eastern Democratic Republic of the Congo, particularly affecting sex workers, and that this virus strain was also known as IIb. suggested that it could spread easily between people as well.

Genome sequencing confirmed that the variant that caused this outbreak contained several important differences from other clade I viruses, and researchers named it Ib. The strain has been detected in the United Kingdom, Sweden, Thailand, India, Germany, and six African countries where no mpox infections had previously been reported. The Democratic Republic of the Congo has been particularly hard hit, with approximately 36,000 suspected mpox cases and more than 1,000 deaths reported in 2024.

But now, nearly a year after researchers discovered an outbreak of clade Ib in eastern DRC, clade Ia is also worrying health authorities. The strain is also increasing in the western region of the DRC and Kinshasa. Especially given that Kinshasa is a travel hub, the prevalence of both Ia and Ib in the capital threatens the 17 million people living there, and the international spread of clade I. increasing the possibility.

Quick guide to monkeypox virus strains

• Clade Ia: The virus has been circulating in Central Africa since it was first discovered to infect humans in 1970. Until recently, it was known that most infections occur in children and that it is transmitted primarily from animals to humans.

• Clade Ib: The strain has caused a surge in cases in Central Africa since it was discovered in late 2023. It is known to be transmitted from person to person through sexual contact.

• Clade IIa: The least studied mpox strain. It is mainly spread to Guinea, Liberia, and Ivory Coast. The route of infection is not completely understood. Although there is no documented evidence of sexual transmission, all forms of close contact may contribute to the spread of infection.

• Clade IIb: This strain is responsible for the 2022 pandemic that is still smoldering. It is known to be transmitted from person to person through sexual contact. The most affected are men who have sex with men.

signs of evolution

Health officials are using genome sequencing tools to track the outbreak. As part of the effort, Mbala and his colleagues sequenced virus samples taken from the Kinshasa outbreak. They found specific patterns of single-letter genetic mutations in samples of both clade Ia and Ib viruses that indicate an ongoing battle between the human immune system and the virus. This pattern is unlikely to emerge unless there is a sustained human presence. Spread to people.

However, this pattern did not appear in the report posted to the preprint server in August. In that study, the team sequenced clade Ia virus samples collected between 2018 and 2024. The researchers found no pattern, suggesting it may be a recent event. “We haven’t seen any strong signs of evolution” in rural and endemic areas of the Democratic Republic of Congo, said Jason Kindrachuk, a virologist at the University of Manitoba in Winnipeg, Canada. He collaborated with Mbala and is a co-author of the August paper. Preprints and virology. “But in Kinshasa, something unique seems to be happening.”

Clade Ia can also be transmitted through sexual contact. Researchers reported the first possible case of sexually transmitted clade I mpox last year, and another similar paper is expected to be published soon, Kindrachuk said.

Kindrachuk wondered why clade Ib suddenly appeared in 2023, given that clade I has been circulating among animals and humans in the Democratic Republic of the Congo since 1970, and why clade Ia has been detected in the past. He added that it will be important to investigate what caused the spike in infections. 2 years. “Is it because we are better at surveillance, or is it because there is more awareness of mpox at the community level? Is it because people have moved more since the pandemic? “Is it due to increased reliance on contact with animals?” he asks.

For now, these findings are unlikely to change plans to begin administering the first mpox vaccine on the African continent, said Nikeise Ndembi, a virologist at the African Center for Disease Prevention and Control in Addis Ababa. said. He said health officials are already allocating doses to areas with high numbers of cases, regardless of the specific strain found there.

This article is reprinted with permission. first published October 30, 2024.