Since at least 2016, the monkeypox virus has been spreading between humans, according to a team of international scientists.
Monkeypox (mpox) shares symptoms with smallpox, such as fever, headaches, and lesions. Historically, humans only contracted the virus from small mammals like monkeys or rodents, not other humans.
An epidemiologist named Áine O’Toole from the University of Edinburgh led a study that found evidence of “sustained human transmission” of the virus outside of African countries where it is known to exist.
These findings represent a significant shift in understanding how the virus spreads, according to O’Toole and her colleagues. They emphasize the importance of new messaging strategies for outbreak management and control.
Scientists first identified mpox in the 1950s after a group of research monkeys in Denmark fell ill. The first human case was officially reported in the Democratic Republic of the Congo in the 1970s.
For many years, human-to-human transmission was rare. Most cases of human mpox originated from various mammals in central, east, and west Africa, although the original source remains unknown.
In 2017, an mpox outbreak occurred in Nigeria, eventually spreading internationally by 2022.
When researchers sequenced the genomes of these global mpox cases, they discovered a lineage of the virus called clade IIb. This lineage is usually not fatal, although it poses a greater risk to individuals with weakened immune systems.
Clade IIb differs from other endemic strains found in Africa, which suggests the possibility of human-to-human transmission.
Most of the mutations found in the clade IIb lineage are characteristic of exposure to a human enzyme with antiviral properties called APOBEC3. This enzyme causes irreversible mutations in the viral genome, altering the sequence of base pairs in a predictable manner.
With each human host the virus encounters, more of these mutations accumulate.
Although this does not necessarily mean that the virus is evolving to spread more easily among humans, it could mean that the human body leaves its mark on the virus.
Regardless, these mutations are rapidly accumulating, indicating significant spread. O’Toole and her colleagues estimate that the human immune system has been battling this particular lineage of the mpox virus for about seven years.
While some human cases of mpox still originate from animals, the researchers conclude that “most cases since 2016 are likely the result of human-to-human transmission” and that this transmission is ongoing.
There may be unrecognized monkeypox epidemics occurring in certain areas, which could lead to outbreaks in other parts of the world through travel.
The authors emphasize that it is crucial for global public health to pay equal attention and concern to mpox virus cases in countries where the virus is known to exist, as well as in other regions. They argue for global surveillance to eliminate the virus from the human population and prevent its re-emergence.
The study was published in Science.
