Mpox Outbreak Linked to Squirrel Consumption in Wild Monkeys

A recent outbreak of mpox among sooty mangabeys in Côte d’Ivoire offers a rare glimpse into the natural transmission cycle of the virus, confirming what scientists have long suspected: rodents, specifically fire-footed rope squirrels, can serve as a source of infection for primates. The findings, published February 11 in Nature, detail how a mangabey likely contracted mpox after consuming an infected squirrel. This discovery has implications for understanding zoonotic transmission – the spread of disease from animals to humans – and refining public health strategies in regions where these animals coexist.

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 investigated the source of the outbreak by analyzing rodents and wildlife carcasses in the area. Their investigation revealed a single positive case among over 700 rodents tested: a fire-footed rope squirrel found dead approximately 3 kilometers from the mangabey troop’s territory, just 12 weeks before the outbreak began. ScienceNews reports that genetic analysis confirmed the viruses from the squirrel and the infected mangabeys were nearly identical, strongly suggesting a direct link.

A Long-Suspected Reservoir

African rodents, particularly squirrels, have long been suspected of harboring the mpox virus. The virus was first isolated from wildlife in a Thomas’s rope squirrel, and their habitats frequently overlap with areas where human mpox cases originate. Even museum specimens of rope squirrels dating back to 1899 have tested positive for the virus, indicating a long-standing presence of the pathogen in these animals. However, direct evidence of transmission from squirrels to other animals, or to humans, has been elusive until now.

Livia Patrono, a veterinarian and disease ecologist at the Helmholtz Institute for One Health in Germany, explained the significance of this finding. “One big question for us has been, ‘where are the nonhuman primates getting infected from?’” she said, as reported by ScienceNews. Years of rodent testing within the park were crucial to pinpointing the fire-footed rope squirrel as a likely source.

Evidence of Consumption

The researchers didn’t rely solely on genetic similarities. Archival video footage from 2014 showed a mangabey from the same troop consuming a fire-footed rope squirrel. To determine if squirrels were recently part of the mangabeys’ diet, the team analyzed fecal samples collected *before* the outbreak. Two samples contained DNA from fire-footed rope squirrels, and crucially, one of those samples as well tested positive for the mpox virus – and came from the monkey believed to be the first infected individual. This provided compelling evidence that the mangabeys were actively consuming squirrels and, in this instance, contracting the virus.

What This Means for Human Risk

While this outbreak occurred within a primate population, the findings have clear implications for human health. Both squirrels and non-human primates are hunted, traded, and consumed by people in West and Central Africa. Exposure to these animals, represents a potential risk for zoonotic transmission of mpox to humans. Clement Meseko, a veterinarian and virologist at the National Veterinary Research Institute in Vom, Nigeria, suggests that public health officials may require to advise individuals who live or function near fire-footed squirrels to take precautions, such as wearing personal protective equipment when handling them or practicing thorough handwashing.

It’s essential to note that this study doesn’t establish the *frequency* of transmission from squirrels to humans. It highlights a plausible pathway and underscores the need for continued surveillance. Researchers emphasize that other rodents likely carry the virus as well, meaning multiple species could pose a threat.

Past Outbreaks and Ongoing Surveillance

Mpox outbreaks among primates in Taï National Park are not new. An infected sooty mangabey was found dead in 2012, and outbreaks affected chimpanzee groups in 2017, and 2018. However, previous investigations revealed that primates themselves weren’t harboring the virus long-term; the virus only circulated during outbreaks. This new research provides the missing piece of the puzzle – identifying the reservoir host that fuels these outbreaks.

Ongoing wildlife monitoring, including fecal sample testing and necropsies, remains critical for understanding the dynamics of mpox transmission. This allows researchers to track the virus’s spread, identify potential spillover events, and inform public health interventions.

What Comes Next: Refining Prevention Strategies

The identification of fire-footed rope squirrels as a source of mpox in mangabeys will likely prompt a reevaluation of prevention strategies in affected regions. Further research is needed to determine the prevalence of the virus in squirrel populations and to assess the risk factors for transmission to humans. This includes investigating the hunting and consumption practices of local communities and identifying opportunities to reduce human-animal contact. Public health messaging may need to be tailored to emphasize the risks associated with handling or consuming these animals. Continued surveillance of both animal and human populations will be essential to monitor the effectiveness of these interventions and to detect any new outbreaks promptly.