Fire-footed rope squirrels identified as a natural reservoir for monkeypox virus

infant mangabey with mpox — HIOH researchers could recently show that sooty mangabeys can contract mpox by eating infected squirrels. The disease may present with mild lesions, as seen in this infant mangabey, but it can also cause more severe skin lesions or even be fatal.

News

02/11/2026

A cross-species transmission event documented in Côte d’Ivoire provides new insights into the spread of mpox in the wild.

Researchers at the Helmholtz Institute for One Health (HIOH), a site of the Helmholtz Centre for Infection Research (HZI), together with an interdisciplinary team of partners, have identified the fire-footed rope squirrel (Funisciurus pyrropus) as a likely natural reservoir of the monkeypox virus (MPXV). Their study was published today in the renowned scientific journal Nature. The discovery was based on the detailed investigation of an mpox outbreak among wild sooty mangabeys (Cercocebus atys) in Taï National Park, Côte d’Ivoire. Scientists combined ecological, behavioral and molecular evidence to document, for the first time, the interspecies transmission of MPXV in the wild, from fire-footed rope squirrels to sooty mangabeys.

Mpox is a zoonotic disease caused by the monkeypox virus (MPXV) that can lead to severe illness in humans. It regularly spills over from wildlife to humans in West and Central Africa, and some of these spillovers have recently sparked large global outbreaks sustained by human-to-human transmission. In order to prevent such outbreaks effectively, it is crucial to gain a thorough understanding of how the virus circulates in wildlife and what triggers spillover events.

A deadly outbreak among mangabeys

Severe mpox-associated skin lesions in an infant sooty mangabey

For decades, the researchers now at HIOH have worked closely with the Taï Chimpanzee Project to monitor the health of wild chimpanzees, sooty mangabeys and other wildlife in Taï National Park, Côte d'Ivoire — a long-term commitment that proved essential to detecting this transmission event. In early 2023, the team identified an outbreak of mpox in a well-studied group of sooty mangabeys: About one third of the group showed clinical signs of disease, and four infants died.

Viral genome sequencing revealed that the virus detected in the infected monkeys was nearly identical to an MPXV strain identified in a fire-footed rope squirrel found dead 12 weeks earlier nearby.

Eating mangaby between trees and leaves — Caught in the act: While mangabeys mostly eat fruits, seeds, and nuts, they occasionally also prey on small rodents such as squirrels – a potential route of pathogen transmission, as confirmed by the new study.

In an attempt to link both observations, the team analyzed fecal samples from the mangabeys, seeking evidence of pre-outbreak MPXV circulation and contact between the host species. One sample collected eight weeks before the outbreak onset contained DNA from both the virus and the rope squirrel, providing strong evidence of interspecies transmission at this moment. Behavioral data supported these findings. Sooty mangabeys from this group have already been observed catching and eating fire-footed rope squirrels, which provides a direct route for the transmission of viruses.

Squirrels under suspicion: now confirmed

Dead specimen of a fire-footed rope squirrel on the forest floor. — The same monkeypox virus (MPXV) strain that was identified in a dead fire-footed rope squirrel was later also detected in infected sooty mangabeys in the same area, confirming the pathogen’s interspecies transmission.

Squirrels have long been suspected as potential reservoirs for MPXV. The first isolation of the virus from a wild animal was from a rope squirrel (Funisciurus anaerythrus) captured in the Democratic Republic of the Congo in 1985. In 2003, imported squirrels infected with MPXV were also among the rodents suspected to have been the source of an mpox outbreak in pet prairie dog owners in the US. Yet, these animals had never been shown to be directly responsible for an outbreak in another species in nature. The new study is a breakthrough that starts unveiling how the pathogen circulates in the wild.

What this means for human health

As hunting pressure has reduced populations of larger game species, rodents such as squirrels are increasingly hunted and consumed by humans, which likely heightens the risk of human exposure and zoonotic transmission of MPXV. Therefore, confirming the direct involvement of fire-footed rope squirrels in interspecies transmission carries important public health implications.

“Identifying the animal sources of the virus and the exposure routes that lead to inter-species transmission are key steps towards understanding spillover mechanisms and developing effective prevention measures to mitigate the risk of transmission to humans,” says Livia V. Patrono, one of the senior authors at HIOH.

The authors recommend increasing awareness among people who come into contact with squirrels and other wildlife, such as children. In addition, they call for a deeper understanding of MPXV ecology in reservoir species – especially squirrels – as well as in intermediate hosts, particularly non-human primates, in MPXV-endemic regions, to strengthen evidence-based prevention strategies.

One Health approach more relevant than ever

HIOH researchers observe wild-life in the forest. — HIOH scientists have been following and observing mangabey groups in Taï National Park for many years, recording their health status by non-invasive sampling, e.g. of feces, and by thoroughly examining any animals found dead in the forest. This systematic long-term monitoring was key to unveiling the transmission of MPXV between species.

The findings underscore the importance of a One Health approach that recognizes the links between human, animal, and environmental health. “This discovery was only possible thanks to long-term ecological research, continuous health monitoring and systematic sample collection in the Taï National Park,” says Fabian Leendertz, senior author, director of HIOH and co-director of the Taï Chimpanzee Project. “We need to maintain and expand this kind of effort to better understand and hopefully reduce the risks posed by emerging infectious diseases, including mpox – we need to strengthen prevention.”

Josef Penninger, Scientific Director of the Helmholtz Centre for Infection Research, adds: “This study also highlights the value of close cooperation with our African partners. Only through strong, trust-based collaborations with local authorities and research institutions can we effectively tackle zoonotic diseases and make an impact, not just regionally, but globally.”

Study information

The study was carried out in collaboration with an international team of researchers from the following institutions:

Taï Chimpanzee Project; Centre Suisse de Recherches Scientifiques en Côte d’Ivoire, Abidjan, Côte d’Ivoire
Université Peleforo Gon Coulibaly Korhogo, Korhogo, Côte d’Ivoire
Senckenberg Museum for Natural History Görlitz, Senckenberg Society for Nature Research, Germany
Friedrich-Loeffler-Institute, Greifswald–Insel Riems, Germany
Dresden University of Technology, Germany
Queen Mary University of London, London, United Kingdom
Claude Bernard University Lyon 1, Lyon, France
German Primate Center, Göttingen, Germany
Université Félix Houphouët-Boigny d’Abidjan-Cocody, Abidjan, Côte d’Ivoire
University of Greifswald, Germany
University Medicine Greifswald, Germany

Within the Helmholtz Institute for One Health, the research involved scientists from the working groups “Ecology and Emergence of Zoonotic Diseases”, “Evolutionary Community Ecology”, and “Pathogen Evolution”.

Original publication

Carme Riutord-Fe, Jasmin Schlotterbeck, Lorenzo Lagostina, Leonce Kouadio, Harriet R. Herridge, Moritz J. S. Jochum, Nea Yves Noma, Ane López-Morales, Donata Hoffmann, Sten Calvelage, Hjalmar Kühl, Alexander Mielke, Catherine Crockford, Liran Samuni, Roman M. Wittig, Martin Beer, Sery Gonedelé-Bi, Jan F. Gogarten, Sébastien Calvignac-Spencer, Ariane Düx, Livia V. Patrono, Fabian H. Leendertz: Transmission of MPXV from fire-footed rope squirrels to sooty mangabeys. Nature (2026). DOI: 10.1038/s41586-025-10086-y

Further information

An animal source of mpox emerges — and it’s a squirrel – A Nature News Feature
How do mpox outbreaks start? Dead baby monkey provides important clue – A Science News Feature
Ein Affenbaby stirbt – und eine außergewöhnliche Spurensuche beginnt – Die Zeit (in German)