The ongoing pandemic has aroused considerable effort to find methods to prevent and control the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes COVID-19 disease. Rapid inactivation devices would be of great help in this area, to prevent viral transmission through aerosols and contact with infected surfaces.
Novel Coronavirus SARS-CoV-2 This transmission electron microscope image shows SARS-CoV-2—also known as 2019-nCoV, the virus that causes COVID-19—isolated from a patient in the U.S. Virus particles are shown emerging from the surface of cells cultured in the lab. The spikes on the outer edge of the virus particles give coronaviruses their name, crown-like. Image captured and colorized at NIAID's Rocky Mountain Laboratories (RML) in Hamilton, Montana. Credit: NIAID
Now, a new study published on the preprint server bioRxiv* in June 2020 reports that the use of deep ultraviolet light-emitting diodes (DUV-LED) can rapidly inactivate the virus, pointing to its potential to contain the viral spread. Globally, the disease COVID-19 has caused over 7.2 million infections and 411,000 deaths as of June 10, 2020.
Persistence of the Virus in the Environment
Infectious SARS-CoV-2 viral particles are found in respiratory specimens, whether bronchoalveolar lavage (BAL), or nasopharyngeal swabs, or even feces.
SARS-CoV-2 was isolated from the urine of a patient recently and has been found in aerosols, on copper, on cardboard, and plastic or stainless steel, for up to 3 hours, 4 hours, 24 hours, and three days respectively. The persistence of the virus for such long periods allows for infection. To prevent such transmission via contaminated surfaces, frequent handwashing, and sanitization with alcohol is recommended, but the efficacy of the latter is in doubt.
Ultraviolet Inactivation of SARS-CoV-2
Recently, a DUV-LED instrument was reported to inactivate microbes of all kinds, at about 250-300 nm. The current paper reports its specific efficacy against SARS-CoV-2, using a strain from a passenger aboard the cruise ship Diamond Princess, docked off the coast of Japan since February 2020.
The isolate was cultured in Vero cells and the viral stock was exposed to the DUV irradiation at 20 mm distance for different times - 1, 10, 20, 30, or 60 seconds – each duration being tested three times. The virus stock was then diluted in a stepwise fashion, in 10-fold steps.
The dilutions were then inoculated again onto cell culture monolayers, which were then processed as usual to allow cytopathic effects (CPE) to emerge from the presence of the infectious virus. A control was also used, which had not been irradiated.
Rapid and Effective Inactivation
The researchers observed a marked CPE in the infected cells, which had not been unirradiated with DUV-LED. On the other hand, those cells which were infected with the virus and irradiated for 60 seconds showed little change. Even more remarkable, the infected cells that were irradiated for 1 second also showed hardly any CPE.
Thus, the plaque assay showed that even short periods of DUV-LED irradiation were capable of rapidly inactivating the virus. After one second of radiation exposure, the titer of infectious virus declined by 88%, and by 99.9% after a 10-second exposure. The researchers say, “These results suggest that DUV-LED drastically inactivated SARS-CoV-2 with irradiation for even a very short time.”
Cytopathic changes in virus-infected Vero cells without DUV-LED irradiation (0 s), or with 122 DUV-LED irradiation for 1, 10, 20, 30 or 60 s.
The Mechanism of Inactivation
UV-LEDs have already been put to use to inactivate several pathogens, including UV-A, UV-B, and UV-C, which operate at 320-400 nm, 280-320 nm, and 10-280 nm. Such instruments are now being used for medical fields.
Among these types of UV irradiation devices, those providing UV-C are the most efficacious in sterilizing the irradiated objects, by producing photodamage in the DNA of the microbes. The UV light produces pyrimidine dimers in the DNA that disrupt the vital processes such as replication of DNA, transcription, and translation, that are required for microbial activity.
These effects eventually lead to microbial inactivation. Of course, this is also influenced by the species and type of microbe, the power of the light, and the environmental conditions.
Plaque formation in Vero cells. Virus solutions irradiated with DUV-LED for several durations 124 were diluted (100-fold) and inoculated to Vero cells. A representative result is shown.
Applications in Medical Environments
The DUV-LED used in the current study produces a narrow wavelength at high power to enable short exposures and repeated use over the long term. The study is the first to show that this mode of sterilization works to inactivate SARS-CoV-2 rapidly.
CPE was seen in the non-irradiated cell cultures infected with SARS-CoV-2 but not in the cells irradiated for 10 seconds. This is a remarkable finding, given the high transmissibility of the virus in community and healthcare settings, and the ability of the virus to survive on a variety of surfaces for hours and even days.
In the absence of an effective vaccine or drugs, and with the presence of neutralizing antibodies still not proved, the availability of a safe and quick method of sterilizing an environment is of great value. The researchers look forward hopefully: “Development of devices equipped with DUV-LED is expected to prevent the virus invasion through the air and after touching contaminated objects.”
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.