A deadly new strain of Mpox is raising alarm

On 14 August officials at the World Health Organisation classified the outbreak of Mpox as a global health emergency. A new strain of the disease has spread beyond the Democratic Republic of Congo for the first time, to at least 12 other African countries.

MPOX IS A viral infection typically found in parts of Africa and spread through contact with infected animals as well as within households. It causes severe fever, flu-like symptoms and a rash of pus-filled blisters across the body. In 2022 the disease, formerly known as monkeypox, spread around the world—cases turned up everywhere from Nigeria to America and Australia. A newly discovered strain of the virus, described by some researchers as the most dangerous yet, now threatens to spread beyond the Democratic Republic of Congo into neighbouring countries such as Rwanda, Burundi and Uganda.

Although much remains unknown about this strain, Jean Claude Udahemuka, a lecturer at the University of Rwanda who has been studying the outbreak, reports fatality rates of approximately 5% in adults and 10% in children. The virus exhibits different transmission patterns and disproportionately affects children. On June 25th the World Health Organisation emphasised the urgent need to deal with the surge of mpox cases in Africa.

The mpox outbreak in 2022 was caused by a different, and less severe form of the virus of the type “clade II”. The new strain was first identified in April in Kamituga, a gold-mining town in Congo’s South Kivu province. Researchers discovered it was a new lineage of the virus, distinct from previously known mpox strains, which they called “clade Ib”. The clade Ib strain has reportedly mutated to become more efficient at human-to-human transmission. This is causing concern about its potential for broader spread. Mpox has been circulating in humans for many years but it also exists in wild animals in several African countries and occasionally jumps to humans, for example through the consumption of bushmeat.

Unlike the mpox outbreak in 2022, which was driven by male-to-male sexual contact, the new strain is spreading through heterosexual contact, particularly among sex workers, who account for about 30% of recorded cases. Researchers estimate that the outbreak began around mid-September 2023. As of May 26th, 7,851 mpox cases and 384 deaths have been reported in Congo (though it is unclear how many are clade Ib infections, as there is likely to be more than one outbreak going on in the country).

In Congo the new strain is behaving quite differently from other strains of mpox, with cases also suggesting transmission through close (non-sexual) contact. Dr Udahemuka reports instances of household transmission as well as an outbreak in a school. It is also just as common in women as in men, and is reported to be causing miscarriages. The risk of international spread appears to be high, with the strain detected in towns near national borders. The new strain has also been found in sex workers from Rwanda and Uganda, a group that is normally quite mobile. With the arrival of the dry season facilitating greater migration, experts fear it is only a matter of time before the virus starts to emerge in neighbouring countries and then spreads worldwide through close contact at international airports.

In April the Africa Centres for Disease Control and Prevention called for an increase in surveillance and contact-tracing efforts. Some experts suggest it would be worth deploying the smallpox vaccine among high-risk groups such as sex workers and health-care workers, as it has been known in the past to offer cross-protection against mpox, which is a related virus. However, the effectiveness of the smallpox vaccine against this new strain remains unknown. Trudie Lang, a professor of global-health research at the University of Oxford, suggests that although there are uncertainties, the vaccine is safe, easy to use and worth trying. There are also trials under way of an antiviral drug known as tecovirimat, with results expected next year.

The situation in the region is complicated by war, displacement and food insecurity. Containment efforts are made harder still by the likelihood of asymptomatic cases, where individuals do not know they are infected but can nevertheless spread the virus to others. Dr Lang emphasises that this, along with the number of mild cases of the infection, are the biggest unknowns in the current outbreak. Preventing this new mpox strain from becoming another global health crisis requires swift and co-ordinated action.

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