How scientists race to understand new Mpox strain in Democratic Republic of Congo

Can you briefly explain the current situation of MPOX in the Democratic Republic of Congo (DRC)?

Leonard Mufula Masirika (LMM): There are currently two isolated outbreaks of MPOX in the Democratic Republic of Congo. Emergence of lineage I The new strain, which is causing cases nationwide and is also a lineage I strain but genetically distinct from previous Mpox viruses, is causing high mortality and severity of illness in South Kivu province.

Trudy Lang (TL): “The number of cases of this new lineage is extremely concerning. This outbreak is also occurring in a fragile area where the Democratic Republic of the Congo borders Rwanda, Burundi and Uganda. The numbers crossing this border are very high, and the local poverty, location off roads and poor infrastructure make it a very challenging place to adequately support and study these cases. This is important.” [containing this disease] It is important that these regions have the capacity and equipment to detect and respond to emergent threats.

How is this new strain different from the one that caused the global MPOX outbreak in 2022?

TL: Generally, there are two types of MPOX virus: clade I and clade II. The 2022 global pandemic was caused by clade II MPOX, transmitted primarily by close sexual contact and involving men who have sex with men. Although the number of cases was high, the mortality rate was relatively low. [death rate]When we first saw this outbreak in South Kivu, we saw sexual transmission, and that's what we suspected. Lineage I is usually associated with bushmeat being brought into a household, and within that household there can be transmission. Here we're seeing person-to-person transmission outside the household, and sexual transmission, and so we suspected that lineage II was occurring in this area.

However, the symptoms of this new strain are very different. Sexual transmission has been confirmed, but there have also been reports of non-sexual transmission (one person infecting another person through direct contact), including caregiver-to-child and mother-to-child transmission.

There is also pregnancy loss in infected women. These differences are very worrying.

The cases we see are typically severe infections. We don't know how many mild cases there are because they are not reported. In clade II mpox, we saw sexual transmission and a rash limited to the genital area.

The new lineage Ib strain causes a generalized rash, possibly genital lesions, and long-lasting symptoms. These severe cases have a 5% mortality rate in adults and a 10% mortality rate in children. The number of less severe cases is unknown, and the overall mortality rate is one of many unknowns.

Besides the rash, what other symptoms are there?

LMM: We're also seeing some secondary effects of the infection – after patients have been discharged from hospital, some return complaining of problems with their eyes, skin or genitals – and we've set up a long-term effects project to study this.

Where has this new strain been detected so far?

LMM:The first outbreak of lineage Ib virus was reported in September 2023 in Kamituga, a gold mining town in South Kivu province in eastern Democratic Republic of the Congo bordering Rwanda and Burundi. The virus spread from there to Bukavu, the capital of South Kivu province. The virus then spread rapidly to other health zones, including near Rwanda-Bukavu border, Riziki, and Kamaniora, near the crossing point between Rwanda and Burundi.

Are you worried it could spread more widely?

LMM: Yes. We are worried that neighbouring countries will soon report the outbreak. Or maybe they are already infected. This is very likely to happen because there are no border controls. Many of the cases in the Democratic Republic of Congo also have links to neighbouring countries. For example, some of the infected people are Rwandan and Burundian sex workers. This is very likely to happen because there are no border controls.

TL: We need to remain vigilant and try to contain this virus in our region as quickly as possible. The first priority should be the local community in this vulnerable area. However, it is also possible that the virus can be brought on board an airplane. We don't yet know enough about person-to-person transmission, the number of asymptomatic or mild cases, or whether people can be infectious before they get sick.

Especially in cases where the infection is sexually transmitted, it can be hidden by just a rash in the genital area, which is important for the possibility of the disease spreading outside the Democratic Republic of the Congo and outside Africa. Another concern is the impact of the dry season. This outbreak started during the rainy season, when roads are not in good condition and mobility is restricted. We are now in the dry season, when people are more mobile and schools are on holiday.

What measures are being taken to contain the spread?

LMM: The Democratic Republic of the Congo has limited resources to control this emerging strain, its epidemiology remains largely unknown, and the country continues to struggle to monitor sudden outbreaks in very remote areas of South Kivu province amid a national MPOX epidemic.

TL: It is also critically important that we detect and better understand the transmission of this virus, so that we can better inform how to best educate communities to protect themselves.

Léandre Murfula Masirika is a research coordinator at the Health Department of South Kivu province, DRC; John-Claude Udahemuka is a molecular biologist and lecturer at the University of Rwanda, Kigali; and Trudy Lang is Professor of Global Health Research and Director of the Global Health Network at the University of Oxford, UK.