On May 19, 2025, Scripps scientists, in collaboration with researchers in Nigeria and Cameroon, announced genomic data has revealed that mpox circulated among humans in Nigeria for eight years before the international outbreak, highlighting the need for improved surveillance.

Historically, most human mpox infections have resulted from zoonotic transmission—meaning from animals to humans—and these spillovers have rarely led to human-to-human transmission. But during the 2022 global outbreak, mpox began spreading readily between people.

The study published in Nature, notes that mpox transmitted among humans in Nigeria for eight years before sparking the international outbreak in 2022. Using genomic tracing, the researchers estimate that the virus’ ancestor first emerged in southern Nigeria in August 2014 and spread to 11 states before human infections were detected in 2017. The findings highlight the need for improved global surveillance and medicines, given the threat of impending pandemics.

Because the virus involved in the 2022 outbreak had an unexpected number of genetic mutations, scientists thought that mpox might have been circulating in Nigeria for much longer than expected. However, due to a lack of genomic data, it was unclear when and where the virus had first emerged, and what had driven its emergence.

To solve this problem, the study’s senior author, Christian Happi, director of the Institute of Genomics and Global Health at Redeemer’s University in Nigeria, organized a Pan-African consortium to share and generate mpox genomic data. The consortium involved researchers and public health agencies in West and Central Africa, with support from international collaborators including Scripps Research. By pooling samples and laboratory methods, the group generated a genomic dataset that is around three times larger than any previous mpox dataset.

They found that most of the viral samples from Nigeria were the result of human-to-human transmission (105/109), while the remaining four were caused by zoonotic spillover. In contrast, all nine mpox samples from Cameroon were derived from isolated zoonotic spillover events.

Using the phylogenetic tree, the team estimated that the ancestor of the human-transmitting mpox virus emerged in animals in November 2013 and first entered the human population in southern Nigeria in August 2014. They also showed that southern Nigeria was the main source of subsequent cases of human mpox: though the virus spread throughout Nigeria, continual human-to-human transmission only occurred in the country’s south. The team also showed that two of the zoonotically transmitted viral samples from southern Nigeria were related to the Cameroonian viruses, suggesting that viruses are traveling across the border.