As mpox continues to trigger localized outbreaks in Africa and sporadic cases elsewhere, scientists warn that the virus is evolving in ways that could set the stage for another global surge. A series of studies, including recent research published in Nature, reveals that new mpox strains are more adept at spreading between humans and may even pose previously unrecognized risks to male fertility.
The 2022 global outbreak, caused by clade IIb, infected more than 100,000 people and marked a turning point in the virus’s history. Unlike earlier clades that primarily spread from animals to humans, clades IIb and the newly emerging Ib strain exhibit enhanced human-to-human transmission, often through sexual contact. Laboratory studies in rodents suggest these strains may be less lethal but more contagious, as infected animals carried high viral loads and developed delayed symptoms, allowing the virus to spread silently.
One particularly concerning discovery comes from experiments showing that clade IIb mpox persisted in the testes of infected mice for weeks, causing tissue damage and impairing sperm production. While these findings have not yet been studied in humans, they raise the possibility that mpox could impact male fertility and establish reservoirs within the reproductive system. Researchers emphasize that much remains unknown, and caution that these evolving strains could gain a foothold in human populations if allowed to circulate unchecked.
Mpox’s history underscores its unpredictable nature. First identified in humans in the 1970s, the virus remained largely confined to sporadic outbreaks in Central and West Africa. That pattern changed in the late 2010s when clade II caused a large outbreak in Nigeria, followed by the global 2022 spread of clade IIb. In 2025, the emergence of clade Ib in dense urban areas mirrored the earlier trajectory of clade II, sparking renewed concern among scientists about another potential international spread.
Public health experts stress the need for vigilance. Boghuma Titanji, an infectious-disease physician at Emory University, told Nature that the virus should not be underestimated: “Mpox belongs to the poxvirus family, so we should not underestimate what it can do if it’s allowed to become firmly entrenched in human populations and continue to adapt.” Continued monitoring, vaccination efforts, and research into transmission pathways are critical to prevent another large-scale outbreak.
As mpox evolves, studies in rodents and early preprints offer a window into how the virus adapts for more efficient human transmission while potentially introducing new health risks. With emerging clades spreading in urban populations and evidence of viral persistence in reproductive tissues, scientists caution that the next global mpox wave could be on the horizon if public health measures do not keep pace with the virus’s rapid evolution.
