A new gene-tracking study in Nature shows that mpox spread among people in Nigeria for 8 years before it sparked a global outbreak in 2022.
Using genomic tracing, researchers from Nigeria, the United States, Cameroon, Ethiopia, and Belgium estimate that the ancestor of the clade 2 mpox virus (mpxv) that ignited an international outbreak beginning in May 2022 first emerged in southern Nigeria in August 2014 and spread to 11 Nigerian states before human infections were detected in 2017.
In light of the findings, the authors write, "We need improved surveillance in the wildlife population in the forest systems to better understand the transmission and maintenance of MPXV in animal hosts," as well as better human surveillance.
"We could have very easily prevented the 2022 multi-country outbreak if countries in Africa were given better access to therapeutics, vaccines, and surveillance technologies," says first author Edyth Parker, PhD, MPhil, a researcher with the Institute of Genomics and Global Health and with the International Biosecurity and Biosafety Initiative for Science, in a Scripps Research news release. "In a vulnerably connected world, we cannot neglect epidemics until they get exported to the Global North."
Creating the virus's family tree
Because the clade 2 virus had an unexpected number of genetic mutations, the authors of the study hypothesized that it might have been circulating in Nigeria much longer than previously thought. So the international team of investigators pooled virus samples and lab methods, generating a genomic dataset three times larger than any previous mpox dataset, according to the release.
We cannot neglect epidemics until they get exported to the Global North.
The researchers analyzed 118 viral genomes from human mpox cases in Nigeria and Cameroon from 2018 to 2023. All were clade 2b, which is now endemic in West Africa. Just 9 of the samples were from Cameroon.
They found that 105 of the 109 viruses from Nigeria were the result of human-to-human virus spread, with the other 4 caused by zoonotic transmission, or mpox spread from animals to people. In contrast, all 9 cases in Cameroon were the result of zoonotic spillover.
Using a phylogenetic tree created from the genomic analysis, the scientists estimated that the ancestor of outbreak strain emerged in animals in November 2013 in Nigeria and first infected people in southern Nigeria in August 2014. They also showed that southern Nigeria was the main source of subsequent cases of mpox in people, as that is where human-to-human spread was sustained, even though the disease transmitted throughout Nigeria.
'Continual risk of re-emergence'
"The ongoing zoonotic transmission in the forested border regions of Nigeria and Cameroon identified in this study underscores the continuous risk of MPXV emergence and/or re-emergence," the study author wrote. "Furthermore, this risk is likely still significantly underestimated owing to under-ascertainment of cases and sparse genomic data."
This risk is likely still significantly underestimated owing to under-ascertainment of cases and sparse genomic data.
Parker said, "Mpox is no longer just a zoonotic virus in Nigeria; this is very much a human virus. But the fact that there's ongoing zoonotic transmission means there's also a continual risk of re-emergence."
"Global health inequities really impede our ability to control both zoonotic and sustained human transmission," she added. "We cannot continue to neglect either the human epidemics in Africa or the risk of re-emergence—not only does it perpetuate suffering in these regions, it means that inevitably there will be another pandemic."
