Mimicry Under the Electron Microscope: Addressing the Misidentification of Coronavirus-Like Structures in Human Tissues

Introduction Electron microscopy is an important technique for detecting SARS-CoV-2 in human tissue, yet its limitations have led to misidentification of structures like viral particles. Clathrin-coated vesicles, coatomer-coated vesicles, multivesicular bodies, and rough ER frequently mimic coronaviruses, leading to false reports of widespread viral presence. Such errors call for the need of specialist interpretation and complementary confirmatory techniques, as EM by itself is frequently not sufficient. Also, osmium tetroxide, which increases contrast, can disrupt antigen recognition, making it difficult to identify viruses in immunogold labeling. Aim of the Study This study discusses the instances of misidentification of coronavirus-like structures in human tissues and suggests remedial action based on morphological characteristics, immunohistochemistry (IHC), in situ hybridization (ISH), and expert opinion. It also analyzes the effect of osmium tetroxide on antigen preservation Material and Methods Electron micrographs of SARS-CoV-2-infected human tissues were analyzed to differentiate between mimicking structures and genuine coronavirus particles, according to size, presence of spikes, and membrane-bound localization. The effect of osmium tetroxide on viral contrast and antigenicity was assessed, with IHC and ISH data providing validation. Results Misidentified structures were found in various tissues with true SARS-CoV-2 particles confirmed in e.g. the lung via IHC and ISH. Conclusion EM is essential for viral detection, e.g. SARS-CoV-2, but mimicry poses a significant challenge. Experience, IHC, and ISH are necessary to prevent misinterpretation. Osmium tetroxide’s effect on antigenicity should be considered when designing immunoelectron microscopy protocols.