FIG. 4.

Histological lesions and ultrastructural detection of MPXV in lung and skin of a nonvaccinated macaque. (a) Edge of typical cutaneous lesion characterized by epidermal hyperplasia, orthokeratotic hyperkeratosis, ballooning degeneration of keratinocytes (arrowhead) with necrosis, and infiltration by inflammatory cells towards the center (arrow). (b) Necrosis of pulmonary alveolar wall, indicated with arrowheads, and flooding of alveolar lumen with fibrin, edema fluid, foamy macrophages, degenerative neutrophils, and necrotic cellular debris. (c) Mature (arrowhead) and immature poxvirus particles in keratinocyte. Bar, 5,000 nm. (d) Poxvirus particles in necrotic alveolar wall. Bar, 5,000 nm. (Inset) Higher magnification of mature poxvirus particle with characteristic dumbbell structure of the core (left) and immature poxvirus particle (right). Sections were stained with hematoxylin and eosin (a and b) or with uranyl acetate and lead citrate (c and d). Original magnification, ×10 (a) or ×40 (b).