A dangerous strain of mpox that is killing children and causing miscarriages in the Democratic Republic of the Congo is the most transmissible yet and could spread internationally, scientists have warned. The virus appears to be spreading from person to person via both sexual and non-sexual contact, in places ranging from brothels to schools. Hundreds of people with the disease, formerly known as monkeypox, have attended hospital in the mining town of Kamituga, South Kivu province, in what is likely to be the “tip of the iceberg” of a larger outbreak, doctors say. Mpox is a virus from the same family as smallpox, and causes flu-like symptoms and pus-filled lesions. Two years ago, an outbreak in Europe and the US that centred on the gay community prompted the World Health Organization to declare a public health emergency. It was the first time mpox had been reported to have spread via sexual contact. That outbreak was caused by clade II of the virus, one of three recognised groupings of mpox and one that has a relatively low death rate. The new DRC outbreak is a mutated form of clade I mpox. Doctors report a fatality rate of about 5% in adults and 10% in children, as well as high rates of miscarriages among pregnant women. Clade I has historically been found in people who eat infected bushmeat, with transmission largely confined to the affected household. Researchers believe the current outbreak began in a bar used by sex workers. At a briefing for journalists, Trudie Lang, professor of global health research at Oxford University, said that when the DRC outbreak was detected last September scientists had assumed it would be clade II, because of the sexual transmission, until genetic testing revealed it belonged to the more virulent strain. It was an “incredibly worrying” situation, Lang said. While smallpox vaccines and treatments helped bring the 2022 outbreak under control, these are not so far available in the DRC. South Kivu is on the border with Burundi and Rwanda and close to Uganda, and there is frequent cross-border travel by local people. Lang said it was unclear how many asymptomatic or mild cases there were, with the long incubation time of the virus increasing the risk of transmission before people realised they were sick. John Claude Udahemuka, a lecturer at the University of Rwanda, who is involved in the medical response to mpox, said: “It’s undoubtedly the most dangerous of all the known strains of mpox, considering how it is transmitted, how it is spread, and also the symptoms.” He said countries should make preparations for the spread of the virus. “Everyone should get prepared. Everyone should be able to detect the disease as early as possible. But more important, everyone should support the local research and local response so that it doesn’t spread.”