The global research effort surrounding SARS-CoV-2, the virus responsible for Coronavirus Disease 2019 (COVID-19), has progressed at an unprecedented rate. However, as the virus is classified as a hazard group 3 pathogen, only laboratories certified as level 3 biosafety (BSL3) facilities are able to study SARS-CoV-2 in its active state. In order to gain a deeper understanding of the structure and function of the virus, effective inactivation methods that would allow labs with lower biosafety clearance to also study SARS-CoV-2 are necessary.
Viral particles can be inactivated by a variety of methods, including the application of heat, alcohol, peroxide, radiation, fixatives, or detergents. However, few inactivation methods support the ability of SARS-CoV-2 to maintain its native morphology. Researchers at the CNRS and University of Montpellier, France investigated the ability of formaldehyde (FA) to inactivate SARS-CoV-2 viral particles while preserving their morphology.
The group compared viral inactivation using FA and heat to evaluate the extent to which each method could keep SARS-CoV-2 structurally intact. Following inactivation treatment by FA at four different concentrations (0.5, 1.0, 2.0, and 3.6%) or heat, viral particles underwent ultra-filtration and direct analysis by AFM to uncover nanoscale morphology. These AFM measurements were performed directly in the BSL3 laboratory using the NanoWizard IV BioAFM.
SARS-CoV-2 was successfully inactivated after incubation at 58°C for 30 mins, but AFM analysis showed severely damaged particles that had lost their spherical shape. All four FA concentrations showed complete SARS-CoV-2 inactivation (when incubated at 20°C for 30 mins), but viral particles were damaged at 2.0 and 3.6% FA. The study also confirmed existing reports that the FA inactivation effect was temperature-dependent and significantly compromised at 4°C.
The inactivation methods described in this study can be used to expand the number of potential laboratories that can conduct SARS-CoV-2 research outside a BSL3 setting. Furthermore, AFM has been shown to be a reliable tool for analyzing SARS-CoV-2 to provide fast, direct qualitative information on viral morphology. By preserving viral morphology, scientists can study the structure and function of non-infectious particles and ultimately contribute to the ongoing efforts to better understand the mechanisms of infection and transmission, as well as the discovery of therapeutics.