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Three coronaviruses (CoVs) have caused global outbreaks in the past 20 years, and with the COVID19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) still underway, methods that can rapidly inactivate these viruses may play a role. a critical role in ensuring public safety and safeguarding personal health.
A recent study posted on the prepress server bioRxiv * in October 2020 reports on the use of heat treatment as a fast and effective way to inactivate potentially lethal viruses at low cost.
Previous methods of inactivation
The main spread of SARS-CoV-2 is by respiratory droplets and aerosols, or by contact with contaminated surfaces. While droplets travel short distances, aerosols can carry virus long distances. If these are deposited on the surfaces, the latter become infectious. Therefore, the environment must be disinfected and viruses inactivated to control viral spread.
Up to now, chemical agents, UV irradiation and heat treatment have been used, but the latter is the most attractive due to the short time required for treatment and the simplicity of application. Coronaviruses are enveloped viruses with a lipid bilayer envelope from which peaks project.
Both the envelope and the peak protein are denatured by heating for more than one minute at 56 ° C.theC or more, reducing viral titers by 6 log10 or more. At a temperature of 56-65 theC, inactivation occurred by heating for 15-60 minutes, but raising the temperature to 70-100 theC, just 1 to 15 minutes was enough to reduce the viral titer by 4.5 log 10. At even higher temperatures (92 theC), a reduction of 6 log10 was achieved by heat treatment at 15 minutes.
Schematic illustration of virus heat inactivation system
Provide proof of concept for rapid heat inactivation
The researchers developed a simple method to expose viruses to extreme heat for very short periods. This system can be adapted to various living spaces and existing heating, ventilation and sewage systems to ensure human safety. This can be adapted to disinfect liquids or viruses in the air and to design instruments to achieve this. This method can also be used to assess the sensitivity of other viruses to heat and to develop a comprehensive approach to heat inactivation of viruses in less than a second.
The current study aims to reduce the time even further, to less than a minute, so that viral particles in air or liquids can be quickly and effectively inactivated in many everyday settings. Beyond this, keeping liquids at high temperatures is not feasible for longer periods, whereas air must be treated almost instantly.
The researchers used a simple, continuous flow heating and cooling method, with the help of a stainless steel capillary tube. This allowed them to examine the effect of heating coronaviruses so that they heat up for just 0.1 to 1 second at a temperature of 35-100 ° C. theC. The findings will be important not only for coronaviruses, but also for other viruses such as dengue virus, influenza virus, and measles virus, all of which are enveloped in lipids with envelope proteins.
The simulated temperature distribution of the entire heat quench system when using an oil bath to apply and the sectional views of positions i – iv are shown in the circle on the right: (A) 125 0.5, 0, 5 s exposure and (B) 170 ℃, 0.1 s exposure. Zone ○ 1 previous oil bath; Zone ○ 2 oil bath; Zone ○ 3 ambient air; Zone ○ 4 Ice bath.
Accurate temperature evaluation
The researchers first found a way to accurately measure the instantaneous temperature of the virus-containing solution during heating by using a thermocouple at the junction of the SS tube. With slower flow, there is a slight drop in the temperature of the measurements, which is corrected by calibrating the curves accordingly.
COMSOL simulation
The researchers then simulated the heat transfer from the SS tube to the coronavirus-containing solution flowing inside the tube, using COMSOL Multiphysics.TM Program. The temperature is found to rise rapidly in the oil bath area, slowly decrease in the air area, and drop rapidly in the ice bath. The effective heat treatment region was designated from the highest temperature reached after the oil bath and just before the ice bath, approximately 9.5 cm long. The simulated exposure time of the solution to be disinfected was approximately twice the set time of ~ 1 second when the applied exposure time was set at 0.5 cm. The simulation was repeated using a higher temperature and a faster flow.
MHV 256 heat inactivation
Coronaviruses are relatively heat stable at room temperature and only above 65 theC viral inactivation begins to occur. At this point, temperature-sensitive viral kill is evident with even small increases in applied temperature, causing a substantial increase in the death rate.
The SARS-CoV-2 viral load is 7 × 106 per mL on average. To test the system’s ability to achieve rapid heat inactivation, the researchers used an exposure of less than one second and found a 6 log 10 or more reduction in viral titer with the 115 ° C oil bath temperature. theC with a residence time of 1 second.
To achieve the same with an exposure time of less than 0.5 seconds, the temperature must be raised to 125 theC or more, while if the time is further reduced to 0.25 seconds, the reduction in viral titer is 5 log10. At 0.1 seconds, effective inactivation is not achieved even at 170 theC.
Using residual infectivity, a new graph showed that virus inactivation required 0.25 seconds at least at an exposure temperature of 85.2 ° C. theC. The fastest heat treatment for complete viral inactivation requires 0.5 seconds, the actual temperature to which the virus is exposed is 83.4ºC. theC.
Transcendence
The researchers conclude: “This is the first experimental result showing that an exposure of less than one second to a high temperature of 300 ° C is sufficient to inactivate the infectivity of CoV. Our study fills the heat treatment gap of less than one second under the actual applied temperature. “
By providing essential data on heat inactivation, researchers have paved the way to develop a fast, inexpensive, and efficient approach to inactivation of coronavirus in real-world settings.
*Important news
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guide clinical practice / health-related behavior, or be treated as established information.
