Can the Sun’s Rays Inactivate Viruses?

In the middle of the coronavirus pandemic, many experts claim that sunlight can have some power in the inactivation of viruses. Fortunately, hot months are approaching, with greater solar exposure on the streets, so there could be a great reduction if it were true that solar radiation has this power. Could this be the reason for the low number of infections in hot areas?

UV radiation from the sun is the primary germicide in the environment. The objective of this study was to estimate virus inactivation by sun exposure . The researchers analyzed published reports of 254nm UV inactivation and compared them to the sensitivities of a wide variety of viruses, including those with double-stranded DNA, single-stranded DNA, double-stranded RNA, or single-stranded RNA genomes. . In addition, they combined virus sensitivity estimates with solar measurements at different geographic locations to predict virus inactivation. Their predictions matched the available experimental data, so this research should be a useful step in understanding and predicting the survival of viruses after they are released into the environment.

Can the Sun's Rays Inactivate Viruses

We tend to assume that viruses pose a lower potential threat for use in biological warfare or bioterrorism than bacterial counterparts, because they are expected to persist for shorter periods when released into the environment. However, viral agents are more resistant and last longer in the environment than previously expected .

Sunlight or, more specifically, UV solar radiation acts as the main natural virucidal in the environment . UV radiation kills viruses by chemically modifying their genetic material, DNA and RNA. Two questions need to be considered in determining the solar inactivation of biotreatment viruses: estimating the UV sensitivity of viruses for which there is little or no experimental data, and estimating solar UV rays at specific geographic locations .

The overwhelming majority of published information on UV virus inactivation has been based on exposure to UVC radiation from a low-pressure mercury vapor lamp (germicide). However, this type of radiation is not found in sunlight that reaches the earth’s surface. Fortunately, the primary photochemical processes that damage viral DNA or RNA occur at all solar UV wavelengths, which vary only in the efficiency of different wavelengths.

The number of bases in DNA or RNA is important in determining sensitivity to UV inactivation , because the more target molecules there are, the more likely it is that the genome will be damaged at a given level of UV exposure. Another important difference in sensitivity between viral nucleic acid types occurs because the most common lethal photoproducts from UV rays are pyrimidine dimers. Because DNA contains thymine, DNA-containing viruses are generally more sensitive to UV damage than RNA-containing viruses.

The overall objective of this study was to assess the extent to which UV rays in sunlight could inactivate various viruses in the environment. Although other variables may affect the survival of viruses in the environment, inactivation by sunlight should provide a baseline to predict the recovery time of contaminated areas after a virus-mediated biological attack.

How could quarantine status be improved?

The scientists found that the action spectra of virus inactivation are similar for all viruses, regardless of genome type. Therefore, a midday solar flux could be “marginally effective” in inactivating viruses relevant to biodefense . For example, a full-day exposure would result in decreased infectivity for the most UV-sensitive viruses.

Although the parameters reported here may be sufficient to estimate viral survival in many settings, experimental research is required to address the various knowledge gaps. Survival of a few selected viruses, or more likely of suitable non-pathogenic viral simulators, should be determined under actual sun exposure at representative locations and times of the year .

Lacking specific experimental data, the researchers determine that the approach can be used to estimate the survival of a wide variety of viruses after their release at any time and place of the year. These estimates of virus survival should be helpful in developing more efficient countermeasures and developing improved quarantine guidelines for cities and other contaminated areas after a viral release.