The assessment on cross immunity with smallpox virus and antiviral drug sensitivity of the isolated mpox virus strain WIBP-MPXV-001 in China

Since May 2022, human mpox cases have increased unexpectedly in non-endemic countries. The first imported case of human mpox in Hong Kong was reported in September 2022. Here we report the isolation and identification of MPXV from the vesicle swabs of this patient. In this research, the vesicle swabs were inoculated in Vero and Vero E6 cells. In addition to observing cytopathic effects (CPEs) in Vero or Vero E6 cells, the isolated virus was identified as mpox virus (MPXV) using quantitative Real-Time PCR (RT–PCR), transmission electron microscopy, and high-throughput sequencing. The experiment also assessed the cross-protective efficacy of sera from the smallpox vaccinated population and preliminarily assessed the inhibitory effect of anti-smallpox virus drugs against MPXV. CPEs can be observed on Vero E6 cells at 24 h and Vero cells at 48 h. The virus particles could be observed by transmission electron microscope, showing typical orthopoxvirus morphology. In addition, F3L and ATI genes which from MPXV A39R, B2R, HA genes which from orthopoxvirus were confirmed by conventional PCR and Sanger sequencing. The next generation sequencing (NGS) suggests that the MPXV strain belongs to B.1 branch of the West African linage, and has a high identity with the sequence of the 2022 ongoing outbreak. PRNT(50) results showed that 26.7% of sera from individuals born before 1981 who had been immunized with smallpox were positive, but no MPXV-neutralizing antibodies were found in sera from individuals born later. All four anti-smallpox virus drugs evaluated demonstrated inhibition of mpox virus.