In July 2022, the World Health Organization (WHO) declared the spread of the rare viral disease mpox, which is caused by the monkeypox virus, a Public Health Emergency of International Concern (PHEIC) as the infection – typically transmitted by sexual contact – began cropping up around the globe.
That outbreak was contained, and in May 2023 an end to the emergency was declared, putting health officials' minds at ease, for a time at least.
But now mpox – which never really went away in many areas of Africa, where it’s endemic – is back, and a new strain has emerged that’s raising alarm bells in disease prevention communities.
The strain itself, which is called clade I, is known to be more lethal than other versions of the monkeypox virus, and has been responsible for isolated outbreaks in Central Africa for decades. But now, according to a preprint article published on medRxiv, it appears to be spreading via sexual contact too – a first for this dangerous variant.
The paper, posted on 15 April, reports 241 suspected cases and 108 confirmed infections in a conflict-ridden region of the Democratic Republic of Congo (DRC). Approximately 30 per cent of the confirmed infections were in sex workers, adding weight to the idea that sexual transmission is a significant vector for transmission.
“The outbreak is concerning because the virus is an evolved strain that has some characteristics that show that it's been transmitted from person to person and also that it might evade diagnostic testing,” Dr Rosamund Lewis, a WHO emergency manager who is technical lead for the global mpox response and based on the ground in the DRC, tells BBC Science Focus.
Lewis explains that the spread of the new strain has likely been ongoing since September 2023, and that coupled with strains already endemic to other regions of the DRC, it represents a serious challenge for health officials.
“We know that it’s touching several health zones here, so there is a possibility that it will move with the people as they move around, move across borders and things like that.”
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What is monkeypox?
The monkeypox virus was first detected in laboratory monkeys in 1958, yet it’s known to infect more than 50 species of mammals. Despite its name, it likely persists most commonly in rodents and other small mammals, rather than monkeys.
Occasionally, the virus makes the leap from animals to humans, a not-uncommon occurrence in the decades since its identification.
More rare, however, is when it begins transmitting between humans, as was the case in Nigeria in 2017, and in 2022 when mpox went global. Both of these outbreaks involved the less virulent clade II strain.
Most people who contract monkeypox fully recover, but some become very sick. During the 2022 global outbreak, 95,340 confirmed cases resulted in 184 deaths.
According to the WHO, common mpox symptoms include “a skin rash or mucosal lesions which can last 2–4 weeks accompanied by fever, headache, muscle aches, back pain, low energy, and swollen lymph nodes”.
Sexual and other forms of physical contact between infected individuals transmit the virus. The 2022 outbreak was primarily, though not exclusively, transmitted among populations of men who have sex with men.
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The current situation
Unlike the 2022 global outbreak, the vast majority of infections in the DRC are caused by clade I.
This year, as of 29 March, the central African country has reported 4,488 cases of mpox, 319 of which have been confirmed. A total of 279 deaths have been reported.
Lewis points out that children are at a particularly high risk, saying: “A young child who has severely swollen lymph nodes and sores in the mouth can't eat, can't drink, develops a high fever. Therefore, they can succumb if they have underlying conditions, such as poor nutrition or malaria.”
Current reports suggest that children younger than 15 account for 70 per cent of cases in the DRC and 88 per cent of deaths. Cases in children are most likely linked to non-sexual human-to-human transmission.
The new sexually transmitted version of the clade I strain was first identified in the mining area of Bukavu in South Kivu, which suggests there is a greater risk of it spreading to neighbouring Rwanda and Burundi.
The European Centre for Disease Control and Prevention (ECDC) has called for careful monitoring of the situation, since travel to Europe from Rwanda is more common than from the DRC. From there, the virus could spread globally once again.
While the situation is doubtless troubling, the ECDC has concluded that based on genomic sequencing of international cases between October 2022 and April 2024, clade I did not make the leap beyond the DRC.
Can the spread be stopped?
The situation in the DRC has been met with a robust emergency response from both the local government and international agencies such as the WHO. Despite this, the spread is not being controlled and mpox cases have now been reported in 23 of the 26 provinces of the DRC.
South Kivu, where a cluster of sexual transmissions has been identified, is grappling with conflict, displacement and food insecurity, posing particular challenges to health authorities battling the spread.
Moreover, many regions of the DRC are rural and remote. “If you want to get somewhere by motorbike it can take two days to get there,” Lewis explains. “That requires human resources and fuel. Getting specimens to a lab can be a multi-day process.”
In response, Lewis explains that teams of health workers are trying to decentralise access to laboratory diagnostics. This should help authorities get to grips with the dynamics of mpox spread in the DRC, which, as the WHO puts it, “are not well understood”.
Treatment for mpox in the first instance, Lewis says, relies on basic clinical care, such as intravenous lines and antibiotics for a secondary infection of the skin lesions. “Those kinds of things we would take for granted in other settings cannot be taken for granted in this setting.”
“For sexual transmission, the response is an approach which you would use for any sexually transmitted infection,” she says.
Vaccines for smallpox – a genetically similar disease to mpox which has now been eradicated – are effective against mpox and are now being made available.
“We know from the global outbreak that these vaccines are effective against mpox, so we fully expect them to be effective in the DRC. However, they’ve not been used in this setting before (...) and we need broader scale deployment,” Lewis says.
Lewis is calling on the international community to respond to the outbreak and provide more resources. “This is going to need a lot of effort to control,” she says.
About our expert
Rosamund Lewis is the emergency manager & technical lead for the global mpox response, as well as the head of the WHO Smallpox Secretariat, a part of WHO Health Emergencies Programme. She is an experienced public health physician with expertise in immunization, communicable diseases, emergency response and global health leadership.
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