**7. Inactivation of non-enveloped viruses by low pH and high pH**

Acids and alkalines, either used alone or in combination with other active ingredients in formulated products, can be an effective means for viral inactivation. Acids may be used for disinfection, sanitization, textile or face mask pretreatment, or viral clearance during biopharmaceutical manufacturing. Alkalines may also be

used for disinfection, sanitization, and viral clearance during biopharmaceutical manufacturing and can be effective against even the least susceptible of pathogens, the prions [58].

It has been widely reported that a low-pH treatment (typically at pH 4 and below) can effectively inactivate most enveloped viruses, although some enveloped viruses, such as bovine viral diarrhea virus, still exhibit a relatively low susceptibility to this treatment pH [22]. The range of susceptibilities of non-enveloped viruses to low pH seems quite scattered and often goes against the "conventional wisdom" that nonenveloped viruses are not susceptible to acidic pH (**Table 6**). For instance, in the


*Medium, culture medium.*

#### **Table 6.**

*Efficacy of low pH against non-enveloped viruses.*

## *Variability and Relative Order of Susceptibility of Non-Enveloped Viruses to Chemical… DOI: http://dx.doi.org/10.5772/intechopen.102727*

family of *Parvoviridae*, human parvovirus B19 has been found to be markedly susceptible to low pH (completely inactivated after 1–2 h treatment at pH 4), whereas animal parvoviruses, such as minute virus of mice, are not inactivated at all under the same conditions. Interestingly, another human parvovirus (type 4) appears to be less susceptible than B19, but more susceptible than minute virus of mice.

The *Picornaviridae* family also exhibits disparity with respect to susceptibility to low pH. For instance, hepatitis A virus, poliovirus, human enterovirus 71, and coxsackievirus A9 display low susceptibility (less than 1-log10 reduction at pH 3–4 for 1–2 h), whereas rhinovirus, foot-and-mouth disease virus, and enterovirus EV-D68 are highly susceptible (more than 4-log10 reduction or complete inactivation at pH 3–4 after 20–45 min). Note that human enterovirus 71, coxsackievirus A9, rhinovirus, and enterovirus EV-D68 are all members of the same genus (*Enterovirus*).

Feline calicivirus and murine norovirus in the family *Caliciviridae* represent another interesting and convincing example that not all viruses within the same family exhibit the same degree of susceptibility. As an example, feline calicivirus is susceptible to low pH, whereas murine norovirus is much less susceptible. Rotavirus and reovirus (family *Reoviridae*) also display low susceptibility to low pH. The low susceptibility of murine norovirus and rotavirus to low pH may not be a surprise, since these viruses naturally exist in the digestive track, which has an acidic environment. Feline calicivirus, on the other hand, acts more like a respiratory virus.

Viruses, both enveloped and non-enveloped, are generally susceptible to high pH. At an environment of pH 12 or above, most if not all non-enveloped viruses would be inactivated, with extent depending both on temperature and contact time. Reovirus, simian virus 40, hepatitis A virus, canine parvovirus, poliovirus, murine norovirus, and Tulane virus seem to be less susceptible than minute virus of mice, feline calicivirus, adenovirus, rotavirus, and foot-and-mouth disease virus. It may be worth noting that the order of susceptibility to high pH seems to be in discord with the hierarchy concept by the greatest degree: in this case, an enveloped virus, bovine viral diarrhea virus, seems to be less susceptible than most, if not all, nonenveloped viruses [22]; parvoviruses are not necessarily less susceptible than many other non-enveloped viruses; and the size of the viral particle does not seem to matter much with regard to the degree of susceptibility (**Table 7**).



*a See Table 1 for abbreviations used for viruses. <sup>b</sup>*

*Medium, culture medium.*

*Entries in purple font indicate results from undiluted or diluted formulations with microbicidal active ingredients.*

#### **Table 7.**

*Efficacy of high pH against non-enveloped viruses.*
