Ultrastructural analysis of monkeypox virus replication in Vero cells.

In early May 2022, the first worldwide monkeypox virus (MPXV) outbreak was reported, with different clinical aspects from previously studied human monkeypox infections. Despite monkeypox medical importance, much of its biological aspects remain to be further investigated. In the present work, we evaluated ultrastructural aspects of MPXV asynchronous infections in Vero cells by transmission electron microscopy (TEM). The viral strain was isolated from a male patient infected during the 2022 outbreak. TEM analysis showed: (i) adhered intracellular mature virus particles before entry of the host cell; (ii) a reorganization of the rough endoplasmic reticulum cisternae into the so-called "mini-nuclei" structure associated with genome replication; and (iii) noticeably different sites within the viral factory presenting granular or fibrillar aspects. We also observed viral crescents, different MPXV particle morphotypes, and cellular alterations induced by infection, such as changes in the cytoskeleton structure and multimembrane vesicles abundance. Taken together, to the best of our knowledge, these results revealed for the first-time ultrastructural aspects of different steps of the MPXV cycle.