To address the global emergence of monkeypox after the 2022 epidemic, a rapid and accurate diagnostic tool is needed at the point of care to identify individuals infected with monkeypox virus (MPXV) to prevent and control the spread of the virus. We designed an antigen-detecting rapid diagnostic test that exclusively detects MPXV without cross-reacting with the vaccinia virus by developing monoclonal antibodies against the MPXV nuclear capsid protein A5L (MPXV-A5L). The test established a limit of detection sensitivity of 0.5 ng/mL of MPXV-A5L, with high sensitivity (87%) for clinical specimens collected from MPXV patients, a qPCR cycle threshold value ≤ 25 and 100% specificity for qPCR-negative samples. The test is an ideal rapid diagnostic tool for supporting clinical decision-making for people suspected of having MPXV infection in resource-poor settings.

The authors have declared no competing interest.

This research was supported by grants from the Japan Agency for Medical Research and Development (AMED) to Masaharu Isobe (19187977, 20333128 and 22723616) and Tatsuhiko Ozawa (JP24ama121010), as well as from The Toyama Pharmaceutical Valley Development Consortium (no grant number assigned) to Masaharu Isobe and Japan Society for the Promotion of Science, Japan (Grant in Aid for Scientific Research B) (22H02875) to Nobuyuki Kurosawa. The funders had no role in the study design, data collection and analysis, publishing decisions, or the preparation of the manuscript.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Ethics committee of University of Toyama gave ethical approval for this work (R2023227). Ethics committee of Tokyo Metropolitan Institute of Public Health gave ethical approval for this work (5 KenKenKen 3712 )

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