Chlorine dioxide (ClO₂) is a powerful biocide with proven efficacy against a wide range of microorganisms, including viruses. Scientific research has been undertaken to understand the virucidal activity and mode of action of chlorine dioxide. Several ways have been identified for viral inactivation by chlorine dioxide, including protein and nucleic acid modification. Read on to understand chlorine dioxide mode of action, so you can choose the right products to use to ensure infection prevention.
What are viruses?
Viruses teeter on the boundaries of what is considered life and are the smallest of all infectious agents. Composed of genetic material, they are encompassed by a protein coat called a capsid. Certain viruses are covered by an additional coat composed of lipids and proteins known as the envelope. Theoretically, 500 million rhinoviruses (which cause the common cold) could fit on to the head of a pin1.
Viruses can only multiply within the cells of other living organisms known as host cells. Therefore, they are referred to as obligate intracellular parasites. Viral infections lead to a myriad of diseases such as COVID-19, measles, influenza, hepatitis and more. The pathogenicity of a virus in humans is determined by:
- Viral affinity
- Entry
- Replication in host cells
It is vital healthcare professionals inactivate and destroy viruses in the immediate environment, reducing the risk of viral infection.
Chlorine Dioxide (ClO2)
Disinfection with ClO2
The oxidative capacity of various biocide agents. The oxidation capacity of chemicals denotes the number of electrons one molecule can accept from its surrounding molecules. For example, microorganisms including multiple part reductions.
Chlorine dioxide (ClO₂) has been used in the water treatment industry for the 100 years, with The World Health Organisation (WHO) approving it for the disinfection of drinking water.
In recent decades, it has been shown to be an effective biocide in solution and gas forms. Effective against:
- Bacteria
- Viruses
- Protozoa
- Yeasts
- Fungi
- Mycobacteria
- Bacterial spores
As an oxidiser, ClO₂ has the capability to obtain electrons from nearby molecules. It can obtain five electrons in total from surrounding molecules, making it a superior biocide to alternative oxidisers. Those alternatives include aqueous chlorine, peracetic acid and hydrogen peroxide, which are only able to gain two electrons2,3.
Virucidal Activity
Viruses are either enveloped or non-enveloped. According to the Centers for Disease Control and Prevention (CDC), enveloped viruses are regarded by scientists as the least resistant group of microorganisms for disinfectants to inactivate. Vegetative bacteria, fungi, non-enveloped viruses, mycobacteria and bacterial spores are all deemed more resistant for disinfectants to inactivate4.
Tristel’s ClO₂ based disinfectants have been tested in accordance with virucidal standards EN 14476 and EN 14675. In the medical area, Murine Norovirus, Poliovirus Type 1 and Adenovirus Type 5 are chosen by scientists for testing, as they are representative of the most resistant viruses. Efficacy against these viruses and compliance with EN 14476 infers efficacy against all viruses.
Murine Norovirus, Poliovirus Type 1 and Adenovirus Type 5 are chosen by scientists for testing, as they are representative of the most resistant viruses.
…Efficacy against these viruses infers efficacy against all viruses.
Tristel chlorine dioxide products are featured in infection control studies concerning Human Papillomavirus (HPV) and SARS-CoV-2. Two examples include:
- Meyers, et al., (2020) – demonstrated Tristel Duo foams and Tristel Trio Wipes System have efficacy against infectious HPV Type 16 and Type 18 on medical devices in a 30-second contact time5.
- Jerry et al., (2020) – Tristel Fuse for Surfaces was used in the decontamination process for COVID-19 patient rooms, patient ward areas and nurses’ station areas6. This study demonstrates that the use of chlorine dioxide alongside other measures is effective in preventing the spread of SARS-CoV-2 from contaminated patient rooms and general ward areas.
Mechanism of Viral Inactivation
Chlorine dioxide reacts with viral components made up of proteins (chains of amino acid residues) and genetic material (nucleic acids). These reactions affect viruses, which leads to their inactivation in several ways.
Further research regarding the mode of action of ClO₂ on viruses and how this active molecule specifically interacts with viral molecules continues to evolve in the scientific community.
Mode of Action on Viral Proteins
Unlike other oxidant chemistries, ClO₂ is highly selective, reacting extremely slowly (or not at all) with most organic compounds which are known to inactivate other oxidising chemistries. However, ClO₂ reacts specifically with the amino acids: cysteine, methionine, tyrosine and tryptophan, and oxidatively modifies them7.
Structure of an enveloped virus – Influenza virus.
Ogata & Shibata (2008), demonstrated that ClO₂ treatment leads to the denaturing of Haemagglutinin (HA) and Neuraminidase (NA) on Influenza A virus. Four model peptides (HA1, HA2, NA1 and NA2) were treated with ClO₂, and were analysed by reverse-phase HPLC. Several novel peptide peaks were found on the chromatograms that differed completely from the original peptide peaks; this indicated that the original peptides were modified covalently by reaction with ClO₂. Covalent modification of the amino acid residues of tryptophan and tyrosine by ClO₂ was confirmed by mass spectrometry (MS). Such modifications of amino acid residues appeared to denature the HA and NA proteins of Influenza A virus. These proteins are essential for viral infectivity and denaturing them consequently inactivated the virus.
Other peptides were also found to be modified at tryptophan and tyrosine residues; this was suggested to be on other vital proteins such as the Matrix-2 (M2) protein in the viral envelope. The M2 protein of influenza A is a proton channel which balances the pH across the viral membrane during cell entry, triggering the release of the viral genome into the host cell, so that viral replication can occur8. A tryptophan residue protrudes into the M2 protein channel and acts as a gate for protons. As ClO₂ reacts with tryptophan in various peptides, it is likely that the tryptophan residue in the M2 protein channel was also modified by ClO₂, resulting in its key functionality ceasing.
Mode of Action on the Viral Genome
It was concluded by Alvarez and O’Brien, (1982), that ClO₂ inactivates polioviruses (non-enveloped) by targeting the viral RNA, therefore, impairing the ability of the viral genome to act as a template for viral replication9. Sedimentation analysis of extracts of HeLa cells infected with ClO₂-inactivated viruses showed a reduced incorporation of uridine (one of the four base units which comprise RNA) into new viral RNA. In this study, the critical target of ClO₂ was recognized as the viral RNA, consequently resulting in the virus being unable to replicate.
Chlorine dioxide has also been observed to inactivate another non-enveloped virus, Hepatitis A virus (HAV), by simultaneously destroying antigenicity and damaging the viral genome. Antigenicity is the capacity of an antigen (located on the capsid of HAV) to bind specifically with a complementary protein, i.e. host cell receptors.
In Li et al., (2004), antigenicity was measured by ELISA (enzyme-linked immunosorbent assay), and the viral genome was analysed by long-overlapping reverse transcription-polymerase chain reaction (RT-PCR) showing that the 5’ non-translated region was damaged by ClO211.
The study concluded that ClO2 reacted both with the viral RNA and with the viral capsid protein, inhibiting HAV from attaching, penetrating, and replicating in host cells. Poliovirus and HAV are both non-enveloped viruses, which are the most resistant to disinfectants. Having efficacy against these viruses infers efficacy against other viruses of similar structure and the less resistant enveloped viruses.
Conclusion
The virucidal activity of chlorine dioxide has been well established by the aforementioned studies and viral efficacy testing according to European and American standards. With this knowledge, the industry is equipped with disinfectants that are tailored for viral infection control. The active ingredient of many Tristel products is a proprietary chlorine dioxide formulation. Various studies have shown that chlorine dioxide reacts with viruses depending on their molecular composition and structure. As research continues these nuances will be elucidated further.
Chlorine dioxide molecules reacting with HAV antigens and RNA, resulting in modifications which impair infectivity12.
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References:
1 Society, M. (2020) Viruses. Available at: https:// microbiologysociety.org/why-microbiology-matters/whatis-microbiology/viruses.html (Accessed: 25 June 2020).
2 Fukayama, M. Y. et al. (1986) ‘Reactions of aqueous chlorine and chlorine dioxine with model food compounds’, Environmental Health Perspectives, Vol. 69, pp. 267–274. doi: 10.1289/ehp.8669267.
3 Miura, T. and Shibata, T. (2010) ‘Antiviral Effect of Chlorine Dioxide against Influenza Virus and Its Application for Infection Control’, The Open Antimicrobial Agents Journal, 2(2), pp. 71–78. doi: 10.2174/1876518101002020071.
4 Centers for Disease Control and Prevention (2008) ‘Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008; Miscellaneous Inactivating Agents’, CDC website, (May), pp. 9–13. doi: 1.
5 Meyers, C., Milici, J. and Robison, R. (2020) ‘The ability of two chlorine dioxide chemistries to inactivate human papillomavirus-contaminated endocavitary ultrasound probes and nasendoscopes’, Journal of Medical Virology, (November 2019). doi: 10.1002/jmv.25666.
6 Jerry, J. et al. (2020) ‘Do established infection prevention and control measures prevent spread of SARS-CoV-2 to the hospital environment beyond the patient room?’, Journal of Hospital Infection. The Healthcare Infection Society. doi: 10.1016/j.jhin.2020.06.026.
7 Noszticzius, Z. et al. (2013) ‘Chlorine dioxide is a sizeselective antimicrobial agent’, PLoS ONE, 8(11), pp. 1–10. doi: 10.1371/journal.pone.0079157.
8 Cady, S. D. et al. (2009) ‘Structure and function of the influenza A M2 proton channel’, Biochemistry, 48(31), pp. 7356–7364. doi: 10.1021/bi9008837.
9 Alvarez, M. E. and O’Brien, R. T. (1982) ‘Mechanisms of inactivation of poliovirus by chlorine dioxide and iodine’, Applied and Environmental Microbiology, 44(5), pp. 10641071. doi: 10.1128/aem.44.5.1064-1071.1982.
10 Thurman, R. B. and Gerba, C. P. (1988) ‘Molecular Mechanisms of Viral Inactivation by Water Disinfectants’, Advances in Applied Microbiology, 33(C), pp. 75–105. doi: 10.1016/S0065-2164(08)70205-3
11 Li, J. W. et al. (2004) ‘Mechanisms of inactivation of hepatitis a virus in water by chlorine dioxide’, Water Research, 38(6), pp. 1514–1519. doi: 10.1016/j.watres.2003.12.021.
12 Thurman, R. B. and Gerba, C. P. (1988) ‘Molecular Mechanisms of Viral Inactivation by Water Disinfectants’, Advances in Applied Microbiology, 33(C), pp. 75–105. doi: 10.1016/S0065-2164(08)70205-3
