The discovery of sustained human transmission of the monkeypox virus marks a significant turning point in our understanding of this infectious disease. For years, experts believed that humans could only contract monkeypox from small mammals such as monkeys or rodents. However, a recent study led by epidemiologist Áine O’Toole from the University of Edinburgh has shed new light on the virus’s spread, revealing evidence of “sustained human transmission” outside of known African reservoirs.
Monkeypox, a virus with symptoms similar to smallpox, was first identified in the 1950s after a group of research monkeys in Denmark fell ill. It wasn’t until the 1970s that the first human case was officially reported in the Democratic Republic of the Congo. At that time, human-to-human transmission was considered a rare occurrence, with most cases being linked to interactions with mammals in central, east, and west Africa. The exact origin of the virus remains unknown.
In 2017, Nigeria experienced an outbreak of monkeypox, which later spread internationally. When scientists analyzed the genomes of these cases, they discovered a lineage of the virus called clade IIb. While this lineage is rarely fatal, individuals with weakened immune systems are at greater risk. What caught researchers’ attention was that clade IIb looked distinct from other endemic strains found in Africa, suggesting possible human-to-human transmission.
Through their investigation, O’Toole and colleagues uncovered a potential mechanism for human-to-human transmission. They found that nearly all the mutations observed in clade IIb were characteristic of exposure to a human enzyme called APOBEC3. This enzyme interacts with the monkeypox virus’s DNA, leading to predictable changes in its genetic sequence. While these mutations do not necessarily make the virus more transmissible among humans, they do offer insight into the virus’s interaction with the human body.
Based on their analysis, O’Toole and her team estimate that the human immune system has been battling this particular lineage of the monkeypox virus for approximately seven years. While some cases still originate from animal interactions, the majority since 2016 are likely the result of human-to-human transmission. The accumulating mutations suggest a significant level of spread, although the exact implications remain uncertain.
The implications of sustained human transmission extend beyond the immediate consequences. There may be regions with ongoing monkeypox epidemics that have yet to be identified, serving as potential sources for outbreaks in other parts of the world through travel. This calls for a global approach to public health, with equal attention and concern given to monkeypox cases in countries historically regarded as having endemic reservoir species.
The discovery of sustained human transmission of the monkeypox virus presents a paradigm shift in our understanding of this infectious disease. With evidence of the virus spreading directly between humans, there is a crucial need for new strategies in outbreak management and control. While further research is necessary to fully comprehend the implications of these findings, it is clear that monkeypox has entered a new era, prompting a reevaluation of public health measures worldwide.