Genomic Study Reveals Early and Widespread Mpox Transmission in West Africa Before 2022 Pandemic

Recent genomic research has uncovered that mpox, a virus traditionally characterized by zoonotic transmission from animals to humans, was circulating and spreading within human populations in West Africa years before the major 2022 global outbreak. Traditionally, most human mpox cases resulted from direct contact with infected animals, with limited human-to-human transmission. However, the 2022 outbreak marked a shift when mpox began transmitting easily among people, leading to international spread.

Published in the journal Nature on May 19, 2025, the study analyzed mpox genomic data collected from Nigeria and Cameroon between 2018 and 2023. The researchers found evidence that the virus was present in humans in Nigeria for at least eight years prior to the outbreak, with the virus’s ancestral strain believed to have emerged in southern Nigeria around August 2014. Transmission spread to 11 Nigerian states before human infections were recognized in 2017.

A significant aspect of the study was the creation of a large genomic dataset through a collaborative effort of researchers and public health agencies across West and Central Africa, supported by international partners including Scripps Research. This dataset was approximately three times larger than previous mpox genomic collections. By examining 118 viral genomes, the team identified that most samples from Nigeria resulted from sustained human-to-human transmission, whereas those from Cameroon were mostly due to isolated zoonotic events.

The phylogenetic analysis indicated that the virus’s common ancestor in humans appeared in animals in November 2013, with the first human cases detected in Nigeria in August 2014. The study also revealed ongoing cross-border viral movement between Nigeria and Cameroon, emphasizing the importance of improved wildlife and human health surveillance. Experts highlight that the disparities in access to diagnostics, vaccines, and therapeutics across Africa have hampered efforts to contain mpox and other zoonotic threats.

Edyth Parker, a senior author of the study at Scripps Research, emphasized that better health infrastructure could have potentially prevented the extensive outbreak in 2022. The findings call for a push toward equitable healthcare resources worldwide, especially in vulnerable regions where zoonotic spillovers can lead to pandemics if left unchecked.

This research underscores the critical need for enhanced global and regional surveillance systems, comprehensive wildlife monitoring, and increased availability of medical countermeasures to avert future epidemics of zoonotic-origin viruses like mpox.