The virus responsible for mpox (formerly known as Monkeypox) was circulating for about eight years ago in West Africa before the 2022 global outbreak, according to a study. The study, published in the journal Nature, highlights the need for improved global surveillance and medicines, given the threat of impending pandemics.
Using genomic tracing, the researchers estimate that the virus's ancestor first emerged in southern Nigeria in August 2014 and spread to 11 states before human infections were detected in 2017.
"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," said Edyth Parker, from the Kristian Andersen Lab at Scripps Research.
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 understand, the team analysed 118 viral genomes from human mpox cases that occurred in Nigeria and Cameroon between 2018 and 2023. All of the sequences were identified as Clade IIb -- the mpox strain endemic to West Africa.
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.
"Mpox is no longer just a zoonotic virus in Nigeria; this is very much a human virus," Parker said. "But the fact that there's ongoing zoonotic transmission means there's also a continual risk of re-emergence."
Further, the study 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.
It 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.
Two of the zoonotically transmitted viral samples from southern Nigeria were related to the Cameroonian viruses, suggesting that viruses are traveling across the border. Overall, the study shows the importance of better access to diagnostics, vaccines, and therapeutics in Africa, the researchers said.