Likely cross-border introductions of MPXV Clade I into the Republic of the Congo from the Democratic Republic of the Congo

BackgroundMpox virus (MPXV) Clade I is endemic in several central African countries and characterized by severe disease and high mortality. Since October 2023, a large-scale Mpox outbreak has emerged in the Democratic Republic of the Congo (DRC), with 22,477 cases and 1,038 deaths reported as of May 26, 2024, and World Health organization (WHO) has declared mpox a public health emergency of international concern on august 14 2024. Twenty-three provinces in the DRC have been affected, 15 of which border another country, including the Republic of the Congo (RoC). The RoC is bordered by five of these affected provinces, increasing the risk of cross-border spread. In the RoC, Mpox cases have historically occurred in the endemic areas of the Likouala department in the north. Recently, suspected cases have emerged outside this region, and it is unclear if these cases are recent spillover events from the DRC outbreaks. Therefore, we performed molecular analyses of these cases in the RoC. MethodsSamples were collected from suspected cases between January and April 29, 2024, in Likouala, Cuvette-Centralle, and Pointe-Noire. Blood samples, skin/oropharyngeal swabs or skin crusts were obtained for molecular diagnosis at the Laboratoire National de Sante Publique (LNSP), Brazzaville. MPXV sequences were obtained and analyzed using newly established Nanopore sequencing methodology and bioinformatic pipeline. FindingsPhylogenetic analysis of sequences shows the clustering of MPXV sequences obtained from cases in RoC with sequences from the ongoing Mpox outbreak in the DRC. In addition, sequences from the RoC show multiple phylogenetic positioning suggesting the occurrence of multiple co-circulating strains in the human population. InterpretationThe close genetic relatedness between sequences from RoC and those from DRC indicates a possible cross-border transmission of MPXV from DRC to RoC. These data highlight the need for implementation of expanded surveillance in countries bordering DRC and RoC, in combination with control measures focused at containing the current outbreaks in DRC and RoC to prevent escalation into a larger-scale epidemic. FundingThis research was supported by the Intramural Research Program of the National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH).