To inactivate viruses

To understand how aerosols change in response to the surrounding environment seconds after being exhaled, the team used an aerosol generator and studied how relative humidity affected the droplets. They found that a decrease in infectivity at low humidity occurs almost immediately, falling to an average of 54 per cent within five seconds of generation.

However, the virus infectivity then remains more stable, only decreasing by an average of 19 per cent over the next five minutes. At high humidity, the reduction in infectivity is more gradual, with a steady loss of 48 per cent within the first five minutes. The rate of decay in survival appears to plateau after 10 minutes, irrespective of the humidity levels. The researchers said that further research will be required to explore for how long this plateau continues, and how much of the virus-laden aerosol survives after 20 minutes.

The team said that the infectivity decreases as the aerosols, reacting with CO2 within the droplets, become too acidic for the virus to survive, especially in high-humidity conditions.

In low humidity, the salts within the droplets crystallise, reducing the infectivity of the virus. Further research is also needed to confirm the degree to which acidity is involved in the airborne loss of SARS-CoV-2 infectivity at high humidity, and to determine the exact mechanism by which the pH rise deactivates the virus.

Regression line equation shown. Data represent three independent experiments. Samples originating in BSL-4 laboratories commonly come in a diversity of volumes.

These results demonstrate that the volume of samples being irradiated has an effect on inactivation, a factor not previously recognized as playing a role in inactivation by gamma radiation. Effect of sample volume on inactivation by gamma irradiation. Viral titers after were determined by TCID 50 assay. Inactivation by gamma irradiation is partly due to the radiation-induced creation of ozone within the air of samples [ 23 , 31 ].

There is some evidence that the indirect mechanisms of inactivation by gamma irradiation, which includes the effects of ozone, is diminished in frozen samples [ 23 ]. Since all of the samples we tested were frozen, it was unclear if the volume of air within the samples would have an effect on gamma irradiation-induced inactivation.

Effect of air volume on inactivation by gamma irradiation. Previous reports provide conflicting data regarding the effect of media content on viral inactivation by gamma irradiation, particularly with frozen samples. The effect of protein content in the non-irradiated samples is likely due to a stabilizing effect on the freeze-thaw of the samples [ 32 ], while the effect of protein content on the irradiated samples is likely due to a combination of stabilization during freeze-thaw as well as the free radical scavenging properties of the proteins in the samples.

Effect of sample media on inactivation by gamma irradiation. Since gamma irradiators are not located within BSL-4 laboratories, live samples are sealed in double plastic bags and transported in leak-proof, shatter-proof containers to the irradiators outside of containment.

To further enhance the biosafety while transporting these samples, we tested whether the addition of a disinfectant to the sealed pouches surrounding the samples would interfere with inactivation by gamma irradiation.

The samples were either not irradiated the non-irradiated samples contained 5 mL MicroChem-Plus per pouch or irradiated with 0. Effect of external disinfectant on inactivation by gamma irradiation. Instead, a probabilistic measure, the sterility assurance level SAL , is frequently used to describe the likelihood that a single infectious pathogen remains in an irradiated sample [ 33 ]. If the D 10 for the pathogen is 0. Considering the starting virus titers that we used in this study of 10 6 TCID 50 units, it is not surprising that the 3 Mrad dosage completely inactivated all of our samples since our calculated D 10 values would achieve an SAL of 8.

Factors that alter the D 10 value by mitigating the ability of gamma irradiation to inactivate a pathogen have a direct impact on both the SAL achieved with a given dose of irradiation as well as the dose of irradiation required to achieve a specific SAL.

We identified two factors, sample volume and solute protein content, which alter the D 10 value by compromising the ability of gamma irradiation to inactivate frozen rVSV-EBOVgp-GFP-containing samples.

Another tested variable, virus concentration, alters the dosage required to achieve a specific SAL but appears not to alter the rate at which viruses are inactivated. Air volume and the presence of external inactivating agent had no impact on inactivation by gamma irradiation. Any samples containing a higher virus concentration, a larger volume, or a higher protein content than those used in experimentally-validated tests would therefore require additional testing prior to them being considered safely inactivated.

Testing under different conditions e. For instance, the air volume of a sample may lead to enhanced viral inactivation when samples are irradiated at non-freezing temperatures due to the possibility of gamma radiation-created ozone contributing to viral inactivation [ 31 ].

Having the sample tubes surrounded by MicroChem-Plus during the transport to the irradiator and while being irradiated represents a useful safety precaution since any virus which leaked would immediately come in contact with a disinfectant [ 34 ]. Thus, the addition of this chemical to sample containers provides enhanced biosafety while the samples are being arranged for irradiation without altering the dosage required to achieve the desired SAL. Reported susceptibilities of viruses to inactivation by gamma irradiation sometimes vary, as seen by looking at their gamma irradiation D 10 values see [ 33 ] for a thorough listing.

Published D 10 values, which are often inconsistent, are likely dissimilar due to differences in protocols used for the testing e. Nevertheless, closely related viruses typically have similar sensitivities to inactivation by gamma irradiation when performed using similar experimental protocols see Table 8 of [ 33 ].

BSL-4 pathogens are nearly all enveloped, single-stranded RNA viruses and are therefore likely to have similar D 10 values. Therefore, the results published here, as well as future irradiation studies using appropriate BSL-2 surrogate viruses, can be used to extrapolate what is likely to be the case for viruses that are restricted to study in maximum containment facilities.

However, although it is likely that the D 10 values of negative-sense RNA BSL-4 viruses are similar to those determined in this study, this remains to be confirmed by inactivation studies using select BSL-4 viruses representing different families of BSL-4 pathogens e. We are grateful to J. Connor, Boston University and R. M conceived and designed the experiments; A. All authors edited the paper. National Center for Biotechnology Information , U.

Journal List Viruses v. Published online Jul Adam J. Hume , 1, 2 Joshua Ames , 2 Linda J. Rennick , 1, 2 W. Find articles by Adam J. Find articles by Joshua Ames. Linda J. Find articles by Linda J. Find articles by W. Paul Duprex. Find articles by John Tonkiss. Andrew Mehle, Academic Editor. In this way, all the air in the room is exposed to the UV lights, so any floating germ is inactivated. UVC lights can also be placed in air ducts to inactivate viruses and other germs in air that moves from one room to another.

High-intensity UVC light can damage the eyes and skin in just a few seconds. Most UVC lamps shine a broad spectrum of UVC wavelengths — nanometers or a specific wavelength of nanometers.

In studies with mice and rats , no damage to the skin or eyes has been found from far UVC light. However, more research is needed to verify that people can be exposed to this wavelength over periods of time without harmful side effects. UVC light has been shown to inactivate the novel coronavirus in experiments. Sunlight does not affect the novel coronavirus as quickly as UVC light.

Ultraviolet lamps intended for medical purposes, such as products that disinfect other medical devices or irradiate part of the human body, that meet the definition of medical device under section h of the Federal Food, Drug, and Cosmetic Act also typically require FDA clearance, approval, or authorization prior to marketing.

UVC radiation can cause severe burns of the skin and eye injuries photokeratitis. Direct exposure: UVC radiation can only inactivate a virus if the virus is directly exposed to the radiation. Therefore, the inactivation of viruses on surfaces may not be effective due to blocking of the UV radiation by soil, such as dust, or other contaminants such as bodily fluids. Dose and duration: Many of the UVC lamps sold for home use are of low dose, so it may take longer exposure to a given surface area to potentially provide effective inactivation of a bacteria or virus.

UVA is also implicated in skin aging and risk of skin cancer. Q: Is it safe to use a UVC lamp for disinfection purposes at home? Direct exposure of skin and eyes to UVC radiation from some UVC lamps may cause painful eye injury and burn-like skin reactions. Never look directly at a UVC lamp source, even briefly. Some UVC lamps generate ozone. Ozone inhalation can be irritating to the airway.

UVC can degrade certain materials, such as plastic, polymers, and dyed textile. Some UVC lamps contain mercury.