Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel betacoronavirus, is the causative agent of COVID-19, which has caused economic and social disruption worldwide. To date, many drugs and vaccines have been developed for the treatment and prevention of COVID-19 and have effectively controlled the global epidemic of SARS-CoV-2. However, SARS-CoV-2 is highly mutable, leading to the emergence of new variants that may counteract current therapeutic measures. Electron microscopy (EM) is a valuable technique for obtaining ultrastructural information about the intracellular process of virus replication. In particular, EM allows us to visualize the morphological and subcellular changes during virion formation, which would provide a promising avenue for the development of antiviral agents effective against new SARS-CoV-2 variants. In this review, we present our recent findings using transmission electron microscopy (TEM) combined with electron tomography (ET) to reveal the morphologically distinct types of SARS-CoV-2 particles, demonstrating that TEM and ET are valuable tools for visually understanding the maturation status of SARS-CoV-2 in infected cells. This review also discusses the application of EM analysis to the evaluation of genetically engineered RNA viruses.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel betacoronavirus, is the causative agent of COVID-19, which has caused economic and social disruption worldwide. To date, many drugs and vaccines have been developed for the treatment and prevention of COVID-19 and have effectively controlled the global epidemic of SARS-CoV-2. However, SARS-CoV-2 is highly mutable, leading to the emergence of new variants that may counteract current therapeutic measures. Electron microscopy (EM) is a valuable technique for obtaining ultrastructural information about the intracellular process of virus replication. In particular, EM allows us to visualize the morphological and subcellular changes during virion formation, which would provide a promising avenue for the development of antiviral agents effective against new SARS-CoV-2 variants. In this review article, we present our recent findings using transmission electron microscopy (TEM) combined with electron tomography (ET) to demonstrate the morphologically distinct types of SARS-CoV-2 particles and the application of EM analysis to evaluate genetically engineered viruses.

Ethanol has variable effectiveness against non-enveloped viruses; however, several reports suggest that it possesses virucidal activity against human adenoviruses (HAdVs). Ethanol concentrations between 45 w/w% and 95 w/w% showed sufficient activity against HAdV type 5 over a 30 s period, while concentration between 72.5 w/w% and 77 w/w% was effective against type 7 over 60 s period. Type 2 and 8 were less susceptible, however. In this study, we investigated the ability of different concentrations of ethanol to inactivate and change the structure of 19 HAdV types across six subgroups, using the virus infectivity titer for evaluation. After 1 min of ethanol treatment, HAdV types 5 and 8 were observed with transmission electron microscopy. The virucidal activity of disinfectant ethanol against HAdVs in subgroups A, B1 (except for type 21), and C was higher than that in subgroups B2, D, E, and F. We observed a ‘U-shaped’ fluctuation pattern where the reduction factor dropped at concentrations of 70–80% and then rose again at 90%. After treatment with 40% ethanol, TEM images showed no major changes in type 8 HAdVs, but organic matter was observed around the virus particles in type 5 HAdVs; after treatment with 66% ethanol, virus particles aggregated in both types. This suggests that HAdVs with a lower number of repeats in the shaft region exhibited higher ethanol resistance.