Isolation and Characterization of Monkeypox Virus from the First Case of Monkeypox — Chongqing Municipality, China, 2022

Introduction The first imported case of monkeypox (MPX) from the mainland of China was reported in September 2022. Herein, the study reports the isolation and characterization of MPX virus (MPXV) in this case. Methods Clinical specimens including skin blister fluid, oropharyngeal and nasopharyngeal swabs, and blood were collected and inoculated onto Vero cells. The isolated virus was identified as MPXV using quantitative polymerase chain reaction (qPCR), cytopathic effects (CPEs), immunofluorescence assay (IFA) and transmission electron microscopy (TEM). Plaque assays were employed to quantify infectious plaque-forming units (PFUs). The plaque reduction neutralization test (PRNT) was developed to determine the neutralizing antibody (nAb) against MPXV. Results MPXV replication was confirmed with qPCR. Typical CPEs were observed 48 h post-incubation. The isolated virus was named MPXV-B.1-China-C-Tan-CQ01. IFA showed that MPXV reacted with serum of MPX case. Orthopoxvirus morphology was observed using TEM. The virus titer increased to >106 PFU/mL after three passages. The serum PRNT 50% neutralization titer (NT50) was 35 for the MPX patient 6 days after symptom onset. Discussion The study successfully isolated the first MPXV strain in the mainland of China, MPXV-B.1-China-C-Tan-CQ01. Infectious titration and PRNT methods have been developed. The study provides key resources and technical platforms for further research as well as anti-viral drug and vaccine development against MPX.