Predicted inactivation of viruses of relevance to biodefense by solar radiation

Abstract

UV radiation from the sun is the primary germicide in the environment. The goal of this study was to estimate inactivation of viruses by solar exposure. We reviewed published reports on 254-nm UV inactivation and tabulated 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. We calculated D(37) values (fluence producing on average one lethal hit per virion and reducing viable virus to 37%) from all available data. We defined "size-normalized sensitivity" (SnS) by multiplying UV(254) sensitivities (D(37) values) by the genome size, and SnS values were relatively constant for viruses with similar genetic composition. In addition, SnS values were similar for complete virions and their defective particles, even when the corresponding D(37) values were significantly different. We used SnS to estimate the UV(254) sensitivities of viruses for which the genome composition and size were known but no UV inactivation data were available, including smallpox virus, Ebola, Marburg, Crimean-Congo, Junin, and other hemorrhagic viruses, and Venezuelan equine encephalitis and other encephalitis viruses. We compiled available data on virus inactivation as a function of wavelength and calculated a composite action spectrum that allowed extrapolation from the 254-nm data to solar UV. We combined our estimates of virus sensitivity with solar measurements at different geographical locations to predict virus inactivation. Our predictions agreed with the available experimental data. This work should be a useful step to understanding and eventually predicting the survival of viruses after their release in the environment.

FIG. 1.

UVA/UVB action spectrum for virus inactivation normalized to 254 nm. The graph shows the relative sensitivity of viruses, calculated as the ratio of D₃₇ at 254 nm to the D₃₇ at the selected wavelength; hence, there are no units. Data represent the mean from n values for diverse viruses at a given wavelength. Values in parentheses indicate the number of data points at each wavelength. The bars represent the standard deviations from the means. Data were obtained from references , , , , , , , , -, , , , , , , and .

FIG. 2.

Solar spectrum (squares) at SZA = 0° (sun directly overhead) (18), UV virus sensitivity normalized to 254 nm (diamonds) (see Fig. 1), and virus inactivation effective spectrum (triangles). The inactivation effective spectrum was calculated by multiplying the solar spectrum times the normalized UV sensitivity at selected wavelengths.

FIG. 3.

Virus inactivation effective spectra at different SZAs. The solar radiometry data are for 0° (from reference 16), 28° and 68° (reference 41), and 37° (reference 81).