What is the impact of heat treatment on monkeypox virus?

In a recent article posted to the bioRxiv* preprint server, investigators determined the inactivation of monkeypox virus (MPXV) by heat treatment.

Study: Heat inactivation of the Monkeypoxvirus. Image Credit: Dotted Yeti/Shutterstock
Study: Heat inactivation of the Monkeypoxvirus. Image Credit: Dotted Yeti/Shutterstock

Background

Numerous cases of monkeypox have been documented in non-endemic nations since April 2022. This unusual outbreak is associated with MPXV, belonging to the Orthopoxvirus genus and Poxviridae family. Most confirmed cases, totaling 31,800 incidents on 9 August 2022, are from the European Region of the World Health Organization (WHO). Males having sex with other males reporting recent sex with new or numerous partners are more likely to be infected.

Increasing numbers of monkeypox cases have been documented over the past 50 years in 10 African nations and four non-African countries since the identification of MPXV in 1958. It is more than exceptional to have this many MPXV instances outside of Africa, emphasizing the need to understand the virus's pathogenesis and transmission.

It is vital to manipulate clinical samples and conduct virus research to combat and halt the current outbreak. Therefore, viral inactivation techniques are required to enable safe experimental laboratory environments.

A frequent method of virus inactivation is heat treatment. Heat is commonly applied to biological samples, Personal Protective Equipment (PPE), hospital equipment, laboratory materials, and transportation media to render viruses inactive. Presently heat inactivation information on Orthopoxviruses is only available for variola and vaccinia viruses. Due to their similar structures, MPXV and the vaccinia virus may be equally vulnerable to thermal inactivation, as previously seen with a biocidal agent.

About the study

In the present research, the investigators heated two media types spiked with two distinct MPXV strains to different temperatures typically employed in laboratories to inactivate viruses for varying lengths of time. Subsequently, the team used the plaque assay technique to assess the strains for remnant infectivity.

The experiments were conducted using Vero E6 cell lines. Among the two MPXV strains used, one was from the Congo basin (designated LK for Lokole area), and another one was from a human patient in France isolated in June 2022 (MPXV/2022/FR/CMIP strain designated CMIP2022). Besides, the virus was titrated using a plaque test.

Two distinct media kinds, i.e., Viral Transport Media (VTM) and FCS, were used to dilute the MPXV strains by half. Further, 200 µl of each sample was exposed in triplicate to different temperatures for durations ranging from 30 seconds to 90 minutes. In a calibrated and validated dry water bath, samples were inactivated and cooled using ice. The researchers then examined their infectivity by a plaque analysis.

The samples were screened at 95°C, 70°C, 60°C, and 56°C temperatures to simulate the typical temperatures used for quick viral inactivation and suitable with molecular biology methods, inactivating MPXV before diagnosis normally, high-treat pathogens inactivation, and serosurveys, respectively. In addition, every experiment followed stringent biosafety level 3 (BSL3) guidelines.

Results

The study results illustrated that the two analyzed MPXV strains were inactivated in most situations, such as 70°C under five minutes and 60°C under 15 minutes. The exceptions were those exposed to 95°C for 30 seconds and 56°C for 30 minutes. MPXV remained infectious following 30 minutes at 56°C, indicating that at least an hour of thermal inactivation is required for serum products to render high titer sera completely inert.

Quantitative polymerase chain reaction (qPCR) results demonstrated that heat treatment weakly influences subsequent viral deoxyribonucleic acid (DNA) sensing by qPCR, with deviations in cycle threshold (Ct) not surpassing 3.46 at 95°C and 2.09 at 60°C and 70°C. This inference implied that the significant proportion of viral DNA remained unchanged among virus particles.

These results suggested that MPXV was somewhat susceptible to heat inactivation in laboratory settings. These data could aid laboratory personnel in strengthening their protocols and serve as a foundation for understanding MPXV survival strategies outside the hosts.

Conclusions

Overall, the study findings showed that MPXV was inactivated at 70°C in less than five minutes and 60°C in less than 15 minutes. There was no variation between viruses from the Central African and West African clades. The current observations could aid laboratory staff in manipulating the virus under the optimum biosafety circumstances and streamlining their procedures.

Notably, the authors mentioned that additional experiments are required to assess MPXV persistence on different matrices at various temperatures and examine the possible function of contaminated surfaces in viral transmission.

*Important notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Shanet Susan Alex

Written by

Shanet Susan Alex

Shanet Susan Alex, a medical writer, based in Kerala, India, is a Doctor of Pharmacy graduate from Kerala University of Health Sciences. Her academic background is in clinical pharmacy and research, and she is passionate about medical writing. Shanet has published papers in the International Journal of Medical Science and Current Research (IJMSCR), the International Journal of Pharmacy (IJP), and the International Journal of Medical Science and Applied Research (IJMSAR). Apart from work, she enjoys listening to music and watching movies.

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