Characterization of UVC Light Sensitivity of Vaccinia Virus

Abstract

Interest in airborne smallpox transmission has been renewed because of concerns regarding the potential use of smallpox virus as a biothreat agent. Air disinfection via upper-room 254-nm germicidal UV (UVC) light in public buildings may reduce the impact of primary agent releases, prevent secondary airborne transmission, and be effective prior to the time when public health authorities are aware of a smallpox outbreak. We characterized the susceptibility of vaccinia virus aerosols, as a surrogate for smallpox, to UVC light by using a benchtop, one-pass aerosol chamber. We evaluated virus susceptibility to UVC doses ranging from 0.1 to 3.2 J/m 2 , three relative humidity (RH) levels (20%, 60%, and 80%), and suspensions of virus in either water or synthetic respiratory fluid. Dose-response plots show that vaccinia virus susceptibility increased with decreasing RH. These plots also show a significant nonlinear component and a poor fit when using a first-order decay model but show a reasonable fit when we assume that virus susceptibility follows a log-normal distribution. The overall effects of RH (P < 0.0001) and the suspending medium (P ‫؍‬ 0.014) were statistically significant. When controlling for the suspending medium, the RH remained a significant factor (P < 0.0001) and the effect of the suspending medium was significant overall (P < 0.0001) after controlling for RH. Virus susceptibility did not appear to be a function of virus particle size. This work provides an essential scientific basis for the design of effective upper-room UVC installations for the prevention of airborne infection transmission of smallpox virus by characterizing the susceptibility of an important orthopoxvirus to UVC exposure.

Review of Vaccinia Virus and Baculovirus Viability Versus Virucides

“…Similarly, Sidwell et al (1966) reported VACV was less stable in high humidity environments (78% RH). In line with these findings, McDevitt et al (2007) showed the survival of aerosolized vaccinia in the presence of UVC is significantly influenced by RH.…”

“…In an earlier study, Jensen (1964) reported VACV is highly susceptible to UVC with >99% viral inactivation with short exposure times. McDevitt et al (2007) found similar results, demonstrating VACV susceptibility to UVC. In 1965, Rauth investigated the UVC sensitivity in the range 225-302 nm for 12 medically important viruses including VACV, and postulated the susceptibility of vaccinia to UV inactivation is the result of its relatively large size and adsorption cross-section compared with those other viruses (Rauth, 1965).…”

“…* Sensitivity of aerosolized virus at predetermined temperature and humidity ranges (Henderson et al, 1999). 0 Sensitivity of aerosolized virus exposed to UVC (254 nm) under the influence of relative humidity (McDevitt et al, 2007). 0 Determination of virus persistence on various surfaces including cotton and wool fabrics (Sidwell et al, 1966); and plant materials (Bullock, 1967).…”

“…Hence, numerous studies have focused on germicidal UV cell (UVC) light (254-nm) for airborne VACV inactivation and the control of microbial infection spread (Jensen, 1964;McDevitt et al, 2007;Rauth, 1965). As evidenced from studies, VACV is readily inactivated by UV light (Henderson et al, 1999).…”

Aerobiology and Inhalation Exposure to Biological Select Agents and Toxins

“…For instance, the viability of agents contained in an aerosol particle can be diminished by deleterious environmental stressors, such as ultraviolet radiation. 46 However, pathogens residing at the core of a larger (> 10 mm) infectious aerosol may experience a protective effect from environmental stressors, depending on the consistency and composition of the carrier fluid (eg, mucus). 36 Particle size does nonetheless determine the initial deposition pattern within the respiratory tract and, ultimately, the ability of the deposited BSAT to initiate disease.…”