Sifang Steve Zhou

By S. Steve Zhou, Cameron Wilde, Zheng Chen, Tanya Kapes, Jennifer Purgill, Raymond Nims and Donna Suchmann

Viral inactivation is typically studied using virus suspended in liquid (liquid inactivation) or virus deposited on surfaces (carrier inactivation). Carrier inactivation more closely mimics disinfection of virus contaminating a surface, while liquid inactivation mimics virus inactivation in process solutions. The prevailing opinion has been that viruses are more susceptible to heat inactivation when suspended in liquid than when deposited on surfaces. In part, this reflects a paucity of comparative studies performed in a side-by-side manner. In the present study, we investigated the relative susceptibilities of the enteroviruses poliovirus-1 and adenovirus type 5 to heat inactivation in liquid versus carrier studies. The results of our side-by-side studies suggest that these two viruses are more readily inactivated when heat is applied to virus deposited on carriers. Decimal reduction values (i.e., the amount of time required to reduce the virus titer by one log10) measured at 46°C displayed the greatest difference between carrier and liquid inactivation approaches, with values ranging from 14.0 to 15.2 min (carrier) and from 47.4 to 64.1 min (liquid) for poliovirus. The corresponding values for adenovirus 5 were 18.2–29.2 min (carrier) and 20.8–38.3 min (liquid). At 65°C, the decimal reduction values were more similar (from 4 to 6 min) for the various inactivation approaches.

Part of the book: Disinfection

By Yutaka Nishihara, Hideo Eguchi and Sifang Steve Zhou

This chapter focuses on viral efficacy evaluations of silver ion (Ag+) formulations against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus associated with the COVID-19 pandemic and feline calicivirus (FCV), a surrogate for human norovirus. The chapter discusses the proposed mechanism of inactivation, with reference to some previously published articles. In addition, it discusses the background/current trend/future view of Ag+ products that have been used widely as surface/environment disinfectants in daily life all over the world. In efficacy studies performed by using the standardized ASTM E1052 methodology, it was found that Ag+ formulated with a low concentration (26% w/w) of ethanol displayed virucidal activity against SARS-CoV-2 and FeCV. These formulations might be useful for preventing the transmission of such viruses and limiting the outbreaks of emerging infectious diseases caused by coronaviruses and caliciviruses. To our knowledge, this is the first report describing the virucidal efficacy of an Ag+ formulation, evaluated by using the standardized ASTM E1052 methodology, for inactivating SARS-CoV-2. Some characteristics of Ag+-based virucides are discussed in this research report/minireview.

Part of the book: Disinfection of Viruses

By Sifang Steve Zhou

Viruses exhibit a marked variation in their susceptibilities to chemical and physical inactivation. Identifying a trend within these variations, if possible, could be valuable in the establishment of an effective and efficient infection control or risk mitigation strategy. It has been observed that non-enveloped viruses are generally less susceptible than enveloped viruses and that smaller sized viruses seem less susceptible than larger viruses. A theory of a “hierarchy” of pathogen susceptibility has been proposed and widely referenced. This concept provides a useful general guide for predicting the susceptibility of a newly emerged pathogen. It also serves as a theoretical basis for implementing a limited scale viral inactivation study that is to be extrapolated onto many other viruses. The hierarchy concept should be interpreted with caution since the actual viral inactivation efficacy may, in some cases, be different from the general prediction. The actual efficacy is dependent on the type of chemistry and application conditions. The order of susceptibility is not always fixed; and viruses within the same family or even the same genus may exhibit drastic differences. This chapter reviews viral inactivation data for several commonly used chemistries against non-enveloped viruses, highlighting the cases wherein the order of susceptibility varied or even flipped. Possible underlying mechanisms are also discussed.

Part of the book: Disinfection of Viruses