Monkeypox Outbreak in Monkeys Linked to Squirrel Consumption

A sooty mangabey consuming a fire-footed rope squirrel may have triggered an outbreak of mpox in a vulnerable primate population in Côte d’Ivoire, according to research published this month in the journal Nature. The outbreak, which began in early 2023, affected roughly one-third of a troop of sooty mangabeys in Taï National Park, resulting in the deaths of four infants.

Researchers from the Helmholtz Institute for One Health and partner institutions identified the fire-footed rope squirrel as a likely natural reservoir for the monkeypox virus. The study marks the first documented instance of interspecies transmission of mpox observed in the wild, pinpointing a specific animal source for the infection.

For years, scientists have suspected African rodents, particularly squirrels, of playing a role in the emergence of mpox, but direct evidence of transmission to humans or non-human primates remained elusive. Extensive wildlife monitoring within Taï National Park, including analysis of fecal samples and necropsies of deceased animals, proved crucial in unraveling the source of the 2023 outbreak. The team tested over 700 rodents, finding the virus in a single fire-footed rope squirrel found dead approximately three kilometers from the mangabey troop’s territory, just 12 weeks before the first cases appeared.

Genetic analysis revealed a close relationship between the virus found in the squirrel and the strain that infected the mangabeys, though not an exact match. This suggests that the squirrel identified was not the sole source, but that other infected squirrels likely contributed to the outbreak. Video footage from 2014 showing a mangabey consuming a fire-footed rope squirrel provided a critical behavioral link. Further analysis of fecal samples collected from the mangabeys before the outbreak confirmed the presence of rope squirrel DNA in two samples, with one also testing positive for the monkeypox virus – and believed to be the first infected monkey.

“That was a pretty, let’s say, informative piece of evidence saying that [a fire-footed rope squirrel] was a very likely source of infection for the mangabeys,” said Livia Patrono, a veterinarian and disease ecologist at the Helmholtz Institute for One Health in Greifswald, Germany.

Mpox outbreaks have occurred among primates in Taï National Park since 2012, including a confirmed case in a sooty mangabey in 2012 and illnesses affecting chimpanzee groups in 2017 and 2018. However, previous investigations revealed that primates themselves were not harboring the virus, suggesting they were contracting it from an external source.

The findings have implications for public health, as viral spillovers from animals to humans are believed to be the origin of human mpox outbreaks. Clement Meseko, a veterinarian and virologist at the National Veterinary Research Institute in Vom, Nigeria, who was not involved in the study, suggested that identifying reservoir animals like the fire-footed rope squirrel could inform preventative measures. These measures might include advising people who live or function near these squirrels to use personal protective equipment when handling them or to practice thorough handwashing.

Researchers acknowledge that other rodents likely carry the virus in the wild, indicating that multiple species may pose a threat of transmission. The study underscores the importance of continued wildlife monitoring to understand the dynamics of mpox circulation and prevent future outbreaks.