Viricidal Effects of Chemical and Physical Agents on Viruses

VIRICIDAL EFFECTS OF CHEMICAL AND PHYSICAL AGENTS ON VIRUSES

Viruses are generally transmitted via surfaces and therefore the use of viricidal disinfectants on hard surfaces and viricidal antiseptics on skin is important. In addition, viruses are often associated with organic materials, such as secretions from the host, blood, faeces etc., which enable them to persist on surfaces for longer periods of time (weeks, months, and rarely years) and to survive better viricidal challenges.

In general, viruses are not particularly resistant to chemical or physical agents, although some exceptions exist. In terms of susceptibility to viricidal agents, small non-enveloped viruses (e.g. poliovirus) are more resistant than large enveloped viruses (e.g. HIV, influenza), the lipid rich envelope being damaged easily by chemical and physical agents. The susceptibility of large non-enveloped viruses varies, but it is generally considered to be between that of the small naked and large enveloped viruses, however some rotaviruses are proving particularly difficult to destroy.

The viricidal activity of biocides (antiseptics, disinfectants) varies and not all biocides show a strong viricidal activity against non enveloped viruses (e.g. cationic biocides, phenolics and alcohols). In addition, biocidal activity depends upon a number of factors, such as concentration, contact time, presence of soiling, and formulation (Chapters 18 and 19). Soiling is particularly an issue with water and foodborne viruses. Indeed, even enveloped viruses can survive for many days on a soiled surface even when exposed to biocides. The interactions between biocides and viruses have been poorly studied. In general, viruses present only a few target sites to biocides, mainly the envelope (when present), glycoproteins, the capsid and viral nucleic acid . Some biocides (e.g. cationic) are likely to interact with the envelope and glycoproteins, inhibiting viral infectivity, without altering the viral capsid and genome. The main target site is most probably the capsid which has been shown to be severely damaged in the presence of highly reactive biocides such as aldehydes (e.g. glutaraldehyde) and oxidizing agents (e.g. peracetic acid, hydrogen peroxide). Less reactive biocides, such as quaternary ammonium compounds (QACs) and biguanides (e.g. chlorhexidine) have been shown to damage viral capsid to a lesser extent, explaining the limited activity of these agents against non-enveloped viruses. The viral genome is the infectious part of the virus and is the ideal target for biocides. The destruction/alteration of the viral nucleic acid would ensure complete viral inactivation. However, only a limited number of reactive biocides, mainly oxidizing agents (e.g. hydrogen peroxide, chlorine dioxide) have been shown to penetrate within the capsid and damage viral nucleic acid, or to damage viral nucleic acid released from a damaged capsid. The nature of the association of the viral nucleic acid with the capsid also plays a role in the susceptibility of the virus to chemical and physical agents. Viruses with a helical capsid structure might be more susceptible since the destruction/alteration of capsid is more likely to cause damage to the viral nucleic acid which is closely associated to this type of structure.

Physical agents such as heat and irradiation are viricidal and play an important role in the control of viral contaminants in pharmaceutical products. Most viruses are susceptible to exposure to temperatures above 60 °C for 30 minutes. Such susceptibility is used for the inactivation of viral contaminants, such as HIV, in blood products. However, other viruses such as the hepatitis B virus are less susceptible and appropriate assurance of the absence of such a virus is needed. Viruses survive well at low temperatures and they can be routinely stored at −40 °C to −70 °C. In addition to thermal processes, UV irradiation and ionizing radiation (γray and accelerated electrons) are viricidal mainly following the destruction of the viral nucleic acid. Ionizing irradiation and thermal processes are used for terminal sterilization processes applied to medical and pharmaceutical products .