Survival of a picornavirus and its infectious ribonucleic acid after aerosolization.

The effect of relative humidity (RH) on the survival of airborne viruses is not uniform. Certain airborne viruses, measles and influenza, for example, survive best when held at low RH values (5, 9). The picornaviruses and adenoviruses, on the other hand, exhibit greatest survival in the airborne state at high RH values (8, 10); at least one virus, pigeon pox, survives quite well regardless of the RH (12). Furthermore, many airborne viruses evince rapid inactivation neither at high nor at low but at midrange RH values, between 40 and 60%. This is particularly true for airborne picornaviruses and vesicular stomatitis virus (1, 11). Because of this inconsistent response to different RH values, one can only conjecture as to the role of intact virus components in the inactivation of an airborne virus. However, a comparison of the survival of an airborne virus with that of its infectious nucleic acid could possibly establish the role of the latter, as well as provide some information concerning the mechanism of inactivation for that particular airborne virus. Mengovirus 37A, a thermostable mengovirus mutant (4), was selected for this study. Besides being a proven source of infectious viral ribonucleic acid (RNA), this strain of the encephalomyocarditis (EMC) group of picornaviruses was expected to exhibit rapid inactivation when aerosolized and held at 40 to 60% RH. Therefore, if any significant differences in survival between aerosols of mengovirus 37A and its viral RNA were to occur, they would be most obvious within the mid-range RH values. The preparation, extraction, and assay in L cells of mengovirus 37A or its RNA, preand postaerosolization, have been described (2, 3). Aerosols of both intact virus and infectious RNA were studied at RH values ranging from 20 to 80% (10% RH increments) at 27 C. The aerosolization and collection of RNA aerosols differed from the methods used for virus aerosols as follows. (i) A modified Wells refluxing atomizer was attached directly to the rotating drum so that the aerosol, with no secondary air dilution or mixing, was introduced directly into a 500liter rotating toroid drum (7). This technique did not increase the RH of the drum by more than 1%. (ii) RNA suspensions (titer, 5 x 105 to 106 plaque-forming units per ml) were aerosolized by operating the Wells atomizer at 10 psi for 15 min (10 min for virus suspension). (iii) Each