Preliminary report on the molecular epidemiology of mpox, South Africa 2024

Mpox is an emerging viral infection and has since May 2022 been reported in a multi-country outbreak involving predominantly previously non-endemic countries. In addition, the number of cases of mpox is also rising in some endemic countries in Western and Central Africa. The disease is a notifiable medical condition in South Africa, with no cases reported before 2022. However, in 2022, coinciding with the peak of a multi-country mpox outbreak, five mpox cases were diagnosed in the country. Genomic sequencing and analysis revealed the presence of a monkeypox virus variant, which was circulating during the multi-country outbreak, namely Clade IIb sub-lineage B.1.7 (hMPXV). After the fifth case was reported in 2022, there were no cases detected for the following 20 months. In May 2024, mpox cases were again detected in South Africa leading to concerns that the virus may have been silently transmitting in the country since 2022. Genomic sequencing and analysis for 22 mpox cases reported during May to September 2024, were compared with sequences obtained from mpox cases reported in South Africa in 2022, and cases that have been reported globally. It was found that the sequences of the 2024 cases analysed in this study, clustered with Clade IIb hMPXV and sub-lineage B.1.20 and B.1.6 sequences. The results indicate that the detection of mpox cases in South Africa was an extension of the ongoing multi-country outbreak. Detection of different sub-lineages of hMPXV indicates reintroductions of the virus in the country since 2022, with local transmission of Clade IIb B1.20 hMPXV.