et al. 1985). In another study, the stability of coliphage T3 was reported when dextrose,

spermine, spermidine-phosphate, thiourea, galacturonic acid, glucosaminic acid, and deuterium

oxide were added to the spray medium (Ehrlich et al. 1964).

 Among environmental conditions, RH is the most important when viral aerosols are

generated by wet dissemination because dehydration is an inevitable condition (Cox 1989).

Songer (1967) studied the effects of RH and temperature on various viral aerosols including

Newcastle disease virus (NDV), infectious bovine rhinotracheitis virus (BR), vesicular

stomatitis virus (VSV), and Escherichia coli B T3 bacteriophage. All of the virus aerosols

presented poorest survival at 35% RH; NDV and VSV survived best at 10% RH, while airborne

IBR and T3 phage survived best at 90% RH. Individual variation of viral aerosols was also

observed in another study where vaccinia, influenza and Venezuelan equine encephalitis (VEE)

viruses were found to exhibit the best stability at 20% RH while poliovirus survived well at 80%

RH (Harper 1961). Indeed, the effect of RH on infectivity of a wide range of viruses such as

poliovirus, influenza virus, coliphage, porcine reproductive and respiratory syndrome virus

(Harper 1961; Ehrlich et al. 1964; Songer 1967; Schaffer et al. 1976; Hermann et al. 2007) have

been investigated. These authors concluded that lipid-enveloped viruses prefer low RH (LRH)

but lipid-free viruses survive better at HRH. However, sensitivity to RH varied among virus

aerosols depending on the individual characteristics of viruses. The molecular structure of virus

is the key parameter that determines its stability and sensitivity to RH, and conditions under

which the nucleic acid remains intact. For example, Dubovi (1971) successfully extracted

infectious nucleic acid of MS2 and phi X 174 from inactivated viral aerosols, and Trouwborst

and de Jong (1973) observed nucleic acid separated from protein coat during inactivation of viral

aerosols at various RHs.