Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV

One thing that is well understood about SARS-CoV-2 is that it is closely related to SARS-CoV. The limited amount of research that is available (see previous posts on this blog) indicate that the inactivation of SARS-CoV in the environment, and in response to various disinfection practices is a reasonable surrogate for the inactivation of SARS-CoV-2. This is a valuable insight since it means that previous studies investigating the inactivation of SARS-CoV can be used to provide realistic insights to the expected inactivation of SARS-CoV-2.

This paper, published in 2004 is a good example of the types of insights from SARS-Cov that are available. It describes how SARS-CoV can be inactivated by ultraviolet light (UV) at 254 nm, heat treatment of 65 °C or greater, alkaline (pH > 12) or acidic (pH < 3) conditions, formalin and glutaraldehyde treatments.

UV radiation

UV light at wavelength 254 nm (UVC) emitted at 4016 μW/cm2 (where μW = 10−6 J/s) was shown to achieve significant inactivation of SARS-CoV after 6 minutes. The text states that this resulted in a “400-fold decrease in infectious virus”, which equates to 2.6 Log10 inactivation. [Note that Figure 1 from the paper appears to indicate around 4 Log10 inactivation, with the reason for the apparent discrepancy unclear, at least to me]. The approximate UV “dose” from this lamp after 6 minutes would be 1450 mJ/cm2.

Unsurprisingly, UV radiation in the UVA spectrum (365 nm) was shown to be ineffective.

Gamma irradiation

Gamma radiation (3000, 5000, 10,000, and 15,000 rad) from a 60Co source was shown to be ineffective.

Heat treatment

Heating at 56 °C achieved significant inactivation after 20 min. However, the virus remained infectious at a level close to the limit of detection for the assay, for at least 60 min, suggesting that some virus particles were stable at 56 °C. At 65 °C, most of the virus was inactivated after 4 min, but again, some infectious virus could still be detected after 20 min. However, complete inactivation (to below the limit of detection of the assay) was observed at 75 °C in 45 min. The authors report that “these results suggest that viral inactivation by pasteurization may be very effective”.

Formaldehyde and glutaraldehyde

The authors examined formalin and glutaraldehyde inactivation by incubating virus samples with formalin or glutaraldehyde at two different dilutions (1:1000 and 1:4000). Neither formalin nor glutaraldehyde, at a 1:4000 dilution, was able to completely inactivate virus at 4 °C, even after exposure for 3 days. At 25 and 37 °C, formalin inactivated most of the virus, close to the limit of detection of the assay, after 1 day, yet some virus still remained infectious on day 3. Glutaraldehyde completely inactivated the virus by day 2 at 25 °C and by day 1 at 37 °C. The authors conclude that “both formalin and glutaraldehyde inactivation maybe effective, if proper conditions are met”.

pH

After exposing SARS-CoV to extreme alkaline conditions of pH 12 and 14 for 1 h, and subsequently reversing the conditions to a neutralised, buffered solution, the virus was observed to be completely inactivated (to below the limit of detection of the assay). However, moderate variations of pH conditions from 5 to 9 had little or no effect on virus infectivity, regardless of the temperature. Highly acidic pH conditions of 1 and 3 also completely inactivated the virus at 25 and 37 °C. However, at cooler temperatures (4 °C), a pH of 3 was not fully effective.

REFERENCE:

Darnell, M. E. R., Subbarao, K., Feinstone, S. M. and Taylor, D. R. (2004) Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV. Journal of Virological Methods, 121(1), 85-91.

https://doi.org/10.1016/j.jviromet.2004.06.006

Published by Stuart Khan

Professor of Civil & Environmental Engineering, University of New South Wales

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