*Disinfection of Viruses*

to public health. In addition, the Priority List serves to promote the development of infection prevention and control (IPAC) "countermeasures" for diseases where such countermeasures are limited or non-existent [1].

In this chapter, we thought it would be of interest to examine the 2021 WHO Priority List (**Box 1**) to see where the public health community stands with respect to IPAC countermeasures for the listed viruses (see section below). The approach that we have taken involved searching the literature for articles pertaining to virucidal efficacies for microbicides evaluated specifically against the listed viruses. In some cases literature for a specific listed virus was not able to be identified, but literature on listed viruses of the same family were available. The mechanisms of action of microbicides for viruses should apply similarly to different members of a given virus family, although intrafamily exceptions do exist [2, 3].

The WHO priority diseases [1] are updated periodically in "a list of disease and pathogens [that is] prioritized for R&D in public health emergency contexts." This tool specifies "which diseases pose the greatest public health risk due to their epidemic potential and/or whether there is no or insufficient countermeasures."

At present, the priority diseases are:


\* Disease X represents the knowledge that a serious international epidemic could be caused by a pathogen currently unknown to cause human disease [1].

#### **Box 1.** *WHO priority disease list.*

It should be noted, as a starting point, that even in the absence of empirical data supporting the virucidal efficacy of microbicides for a given emerging or reemerging virus or mutational variant of a known virus such as emerging variants of SARS-CoV-2, disinfection options still are available for IPAC. For instance, the United States Environmental Protection Agency (U.S. EPA) has invoked an Emerging Viral Pathogen Guidance for Antimicrobial Pesticides [4, 5] specifically to deal with just such a possibility. As stated in the associated U.S. EPA web page, the guidance provides a "process that can be used to identify effective disinfectant products for use against emerging viral pathogens and to permit registrants to make limited claims of their product's efficacy against such pathogens." The actual

guidance (Guidance to Registrants: Process for Making Claims against Emerging Viral Pathogens not on EPA-registered Disinfectant Labels) [5] outlines "a voluntary two stage process, involving product label amendments and modified terms of registration and applies only to emerging viruses" [4].

The underlying principle driving the U.S. EPA Guidance for Antimicrobial Pesticides is that of the hierarchy of susceptibility of pathogens to microbicides (the so-called Spaulding Classification [6]). In the U.S. EPA guidance [5], viruses are classified into three categories, ranked from lesser to greater susceptibility to microbicides: small, non-enveloped viruses; large, non-enveloped viruses; and enveloped viruses. A revised hierarchy of susceptibility of pathogens to microbicides [7–10] spans the range of susceptibilities from most susceptible (enveloped viruses) to least susceptible (prions). This known hierarchy of susceptibility of pathogens to microbicides gives the public health community a starting point for IPAC countermeasures to be used for emerging pathogens, per the U.S. EPA [4].
