Infectious respiratory particles exhaled by Clade IIb Mpox virus-infected macaques

The respiratory viral shedding pattern of Mpox patients and the airborne transmissibility remain unclear. It is often challenging to determine the initial exposure time and infective dose at the time of exposure in Mpox patients, making it impractical to track the viral shedding pattern in human Mpox cases. Therefore, we monitored respiratory viral shedding in macaques experimentally infected with Clade IIb Mpox virus (MPXV), as well as the contamination of the ambient air. Our study shows MPXV-infected macaques had obvious symptoms, high respiratory viral shedding and continuous virus-laden particle release. The viral load in both exhaled particles and air within the isolator peaked at 11 d post infection (1.58 × 10¹⁰ copies/macaque/hour and 1.9 × 10⁷ copies/L respectively). Most virus-laden particles (from macaques and air within the isolator) were coarse particles (>7 μm); during peak viral emission, 94%-97% of exhaled particle viral copies and 87%-97% of air within the isolator ones concentrated here. Infectious viruses were present in the exhaled coarse particles of macaques and, in some cases, in particles from the air within the isolator, but not in fine particles. This study provides evidence supporting the airborne transmission of MPXV and suggests that respiratory coarse particles may play a more significant role than fine particles in driving this mode of transmission.