VIROLOGY
After X-ray irradiation, sterility testing is carried out to ensure that the virus is no longer viable by serial culture of the irradiated material in vitro, in a suitable susceptible cell line
UKHSA scientists in the Diagnostics and Pathogen Characterisation Department at Porton Down have pioneered methods for the X-ray irradiation of viruses.
have been detected by transmission electron microscopy and viral antigens are specifically identified by enzyme- linked immunosorbent assay (ELISA).3 In addition, there is no residual toxic material present which could inhibit downstream assay development. X-rays are composed of highly penetrative photons that traverse multiple layers of packaging to penetrate and damage the nucleic acids within the virus preparations, thus rendering the virus replication deficient. The radiation dose required to reduce the viral infectivity titre by 90% (or 1-log10
) is referred to
as a D-value. This can be calculated by subjecting the virus to incremental doses of X-ray irradiation and then titrating each sample to determine the drop in viral infectivity with increased doses of X-ray irradiation. The relationship between X-ray dose and the reduction in viral titre can then be used to determine the D-value, which can be multiplied by a known titre of virus to calculate the inactivation dose. The dose required for inactivation is dependent on the size, concentration and genetic composition of the virus and therefore needs to be determined for each virus.
After X-ray irradiation, sterility testing is carried out to ensure that the virus is no longer viable by serial culture of the irradiated material in vitro, in a suitable susceptible cell line. This is backed up by
nucleic acid extraction and real-time RT- PCR to look for any reduction in ct value, indicating virus replication. High consequence pathogens (Advisory Committee on Dangerous Pathogens hazard group 3 and, potentially, hazard group 4 viruses) can be contained in multiple layers of protective packaging so that they can be safely irradiated. In-house studies comparing the antigenic characteristics of live and irradiated SARS-CoV-2 and mpox in an LFD and ELISA format have shown them to have similar properties to the live virus. NCPV currently has irradiated SARS-
CoV-2 and mpox virus available through its website and the organisation is hoping to expand the range as further viruses are irradiated.
References 1 Peto T. UK COVID-19 Lateral Flow
Oversight Team. COVID-19: Rapid antigen detection for SARS-CoV-2 by lateral flow assay: A national systematic evaluation of sensitivity and specificity for mass-testing. EClinicalMedicine. 2021;36:100924. doi:10.1016/
j.eclinm.2021.100924.
2 Eyre DW, Futschik M, Tunkel S et al. Performance of antigen lateral flow devices in the UK during the alpha, delta, and omicron waves of the SARS-CoV-2 pandemic: a diagnostic and observational study. Lancet Infect Dis. 2023;23(8):922- 932. doi:10.1016/S1473-3099(23)00129-9.
X-rays are composed of highly penetrative photons that traverse multiple layers of packaging to penetrate and damage the nucleic acids within the virus preparations, thus rendering the virus replication deficient
WWW.PATHOLOGYINPRACTICE.COM JUNE 2024
3 Afrough B, Eakins J, Durley-White S et al. X-ray inactivation of RNA viruses without loss of biological characteristics. Sci Rep. 2020 Dec 8;10(1):21431. doi:10.1038/ s41598-020-77972-5.
4 Eakins JS, Afrough B, Hewson R. Monte Carlo modelling of an X-ray chamber for providing inactivation exposures to viruses. J Radiol Prot. 2021 Nov 11; 41(4). doi:10.1088/1361-6498/ac2f85.
5 Mariotti D, Bettini A, Meschi S et al. Effect of chemical and physical agents on monkeypox virus infectivity and downstream research applications. Virology. 2024;592:109993. doi:10.1016/j. virol.2024.109993.
6 Loveday EK, Hain KS, Kochetkova I et al. Effect of Inactivation Methods on SARS- CoV-2 Virion Protein and Structure. Viruses. 2021 Mar 26;13(4):562. doi:10.3390/ v13040562.
7 Möller L, Schünadel L, Nitsche A, Schwebke I, Hanisch M, Laue M. Evaluation of virus inactivation by formaldehyde to enhance biosafety of diagnostic electron microscopy. Viruses. 2015 Feb 10;7(2):666-679. doi:10.3390/ v7020666.
Dr Jane Burton, NCPV Team Leader Teresa Ramalho, NCPV Virologist
The National Collection of Pathogenic Viruses (NCPV)
NCPV is one of four Culture Collections of the UK Health Security Agency and offers a number of services such as safe deposit storage of viruses, providing a safe, secure backup to the customer’s own storage facility. It stores and carries out viability testing on virus patent deposits on behalf of ECACC, and undertakes any virological investigations require.
NCPV preserves well characterised, authenticated human pathogenic viruses in a secure facility, and supplies the agents, or nucleic acids derived from them, to the scientific community according to national and international guides.
www.culturecollections.org.uk/ products/viruses/
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