Researchers Suggest Squirrels, Not Monkeys, Could Be the Source of Mpox

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A preliminary study traces an mpox outbreak in a group of Ivory Coast monkeys to the fire-footed squirrel, indicating the rodent may be a natural reservoir for the virus

Lillian Ali – Staff Contributor

April 18, 2025 10:52 a.m.

In the West African nation of Ivory Coast, a concerning health crisis unfolded as a baby sooty mangabey monkey became gravely ill, presenting an alarming array of symptoms, including painful red blisters covering its body. Tragically, the monkey succumbed to the illness just three days later. In the following months, the infection quickly spread through the troop, ultimately affecting around 25 monkeys—approximately one-third of the group—and resulting in four fatalities.

This outbreak has been linked to mpox, a disease caused by the monkeypox virus, which bears resemblance to the viruses responsible for smallpox and cowpox. The term “mpox” stems from the initial identification of the condition in laboratory monkeys in 1958. However, recent analysis indicates that the source of the outbreak in this specific group of monkeys was not the infant but rather the mother, whose diet included the fire-footed rope squirrel.

Research teams from the Helmholtz Institute in Germany, who have been monitoring these sooty mangabeys in Taï National Park since 2001, seized the opportunity to investigate this outbreak. By leveraging extensive footage and biological data gathered over the years, coupled with virus samples obtained from local wildlife, researchers were able to identify a genetic match between the virus infecting the monkeys and that from the implicated fire-footed rope squirrel. Their preliminary findings, under peer review, were recently disclosed via a preprint in Nature Portfolio.

This early intervention stands in contrast to typical research practices, which often commence weeks or months post-outbreak. The researchers’ ongoing observations allowed them to accurately trace the virus’s origins to the fire-footed rope squirrel, a species native to West Central Africa.

Lead researcher Fabian Leendertz, a wildlife veterinarian, expressed astonishment at the clear correlation between the findings, remarking on the coherence of the evidence.

In the course of their study, researchers meticulously examined numerous rodent and shrew remains for mpox traces and identified one promising candidate: a fire-footed rope squirrel carcass discovered not long before the outbreak. Video analysis revealed that the monkeys consume these squirrels, and genetic testing on fecal samples from the mother monkey showcased the presence of the virus, indicating she had recently fed on one. Notably, she exhibited no symptoms despite being infected, thus contributing to the community’s eventual outbreak.

This research presents the first indication that these squirrels might play a role in transmitting the virus to primates. Yap Boum, a biologist from the Africa Centers for Disease Control and Prevention, posits that connections to these squirrels may also explain certain human mpox cases.

The fire-footed rope squirrel is being considered as a potential reservoir for the mpox virus—an organism that can harbor a pathogen without suffering from its effects. This phenomenon is notably observed in bats, known carriers of various diseases, including Ebola and coronaviruses. Nonetheless, the precise role of fire-footed rope squirrels in the dynamics of mpox transmission remains ambiguous. Délia Doreen Djuicy, a disease ecologist, suggests that more research is required to ascertain whether these squirrels function strictly as reservoir hosts or simply as vulnerable participants in the transmission chain.

Additionally, Leandre Murhula Masirika, who previously identified a new mpox strain, emphasized the potential of fire-footed rope squirrels in this context, noting the persistence of antibodies against the virus in these squirrels. Historical data reveals a pattern of mpox outbreaks in regions where consumption of rope squirrels is prevalent, further supporting their potential role as disease reservoirs.

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