Multiplicity reactivation and radiation survival of aggregated vaccinia virus. Calculation of plaque titer based on MR and particle aggregation seen in the electron microscope

Inactivation and tailing during UV254 disinfection of viruses: contributions of viral aggregation, light shielding within viral aggregates, and recombination

UV disinfection of viruses frequently leads to tailing after an initial exponential decay. Aggregation, light shielding, recombination, or resistant virus subpopulations have been proposed as explanations; however, none of these options has been conclusively demonstrated. This study investigates how aggregation affects virus inactivation by UV(254) in general, and the tailing phenomenon in particular. Bacteriophage MS2 was aggregated by lowering the solution pH before UV(254) disinfection. Aggregates were redispersed prior to enumeration to obtain the remaining fraction of individual infectious viruses. Results showed that initial inactivation kinetics were similar for viruses incorporated in aggregates (up to 1000 nm in radius) and dispersed viruses; however, aggregated viruses started to tail more readily than dispersed ones. Neither light shielding, nor the presence of resistant subpopulations could account for the tailing. Instead, tailing was consistent with recombination arising from the simultaneous infection of the host by several impaired viruses. We argue that UV(254) treatment of aggregates permanently fused a fraction of viruses, which increased the likelihood of multiple infection of a host cell and ultimately enabled the production of infective viruses via recombination.

Effect of surfactants, temperature, and sonication on the virucidal activity of polyhexamethylene biguanide against the bacteriophage MS2

BACKGROUND

Virucidal compounds are essential in preventing the transmission of viral infection in the health care environment. Understanding their mechanisms of action is necessary to improve their efficacy. Inactivation of viruses is less documented than that of bacteria notably because different types of virus have diverse response to microbicides, making difficult to establish an inactivation pattern.

METHODS

The effect of viral aggregates on the virucidal activity of polyhexamethylene biguanide-based microbicide VANTOCIL TG (Arch Chemicals, Manchester, UK) against the bacteriophage MS2 was investigated by using in combination a standard suspension efficacy test under different conditions and dynamic light scattering measuring the presence and size of aggregates.

RESULTS

Temperature had a key role in increasing significantly the virucidal activity of VANTOCIL TG, reducing virus concentration by 4-log(10) within 10 minutes at 40 degrees C. The high temperature was linked to a reduction of viral aggregates despite the exposure to the biguanide. In addition, the viral inactivation kinetic became significantly more linear at 30 degrees C and 40 degrees C. Such results were also observed with sonication during treatment, where a first-order kinetic was observed. However, the addition of surfactants, even though there was evidence of a decrease in viral clumps, did not enhance the virucidal activity of polyhexamethylene biguanide.

CONCLUSION

The presence of viral aggregates was an important factor in the virucidal efficacy of the biguanide as demonstrated by the correlation among high temperature, decrease in aggregates, and increase in activity, although it is possible that high temperatures might also cause conformational changes of the viral capsid, increasing the sensitivity of virions to the microbicide.

Protection of vaccinia from heat inactivation by nucleotide triphosphates

The presence of adenosine triphosphate, guanosine triphosphate, cytosine triphosphate, or uridine triphosphate reduced the rate of inactivation of vaccinia when heated at 50 C. The virus-associated nucleoside triphosphate phosphohydrolases (adenosine triphosphatase, guanosine triphosphatase, cytosine triphosphatase, and uridine triphosphatase) and ribonucleic acid polymerase were also protected from heat inactivation by these compounds. These obervations are best explained by postulating that ribonucleoside triphosphates bind to enzymes in the virus particle, and that these enzyme-substrate complexes are more resistant to thermal denaturation than are the enzymes without their substrates. The kinetics of heat inactivation of the vaccinia ATP phosphohydrolase activity is biphasic, suggesting that there are two proteins in the vaccinia particle that have this enzyme activity but they have different kinetics of heat inactivation. Any of the vaccinia-associated nucleotide phosphohydrolase activities are protected from heat inactivation by the presence of any one of the respective nucleoside triphosphates. This observation suggests that there is a single enzymatic site in vaccinia that is able to react with any ribonucleoside triphosphate.

Target volume analysis of vaccinia virus: influence of virus dispersion and noninfectious particles

These data indicate that 90% of monodisperse vaccinia virus (VV) has a D(37) dose of 1.0 x 10(4) +/- 0.2 x 10(4) rad when exposed to the direct effect of gamma radiation from (137)Cs and (60)Co sources. This D(37) dose yielded a targt size of approximately 10(8) daltons, close to the molecular weight of VV deoxyribonucleic acid. This target corresponds to the first component of the survival curve of VV. Noninfectious virus seemed to play a role on the slope and the proportion of the survival curve second component, suggesting that multiplicity reactivation takes place.

Efficient filtration and sizing of viruses with membrane filters

Untreated membrane filters retain viruses by adsorption, as well as by physical restriction which occurs when the pore diameter of the filter is smaller than that of the virus particle. As originally recommended by Elford, membranes had to be pretreated with proteinaceous material to preclude virus adsorption. However, coating materials that prevent adsorption of certain viruses do not necessarily prevent adsorption of other viruses. In contrast to proteins, salts enhance virus adsorption. Viruses treated with sodium lauryl sulfate to reduce the surface tension, or purified viruses in distilled water, are not adsorbed to membranes. A procedure is recommended by which viruses may be passed through membranes with a porosity twice the diameter of the virus. Such filtrates, which contain 50 to 100% of the initial virus concentration, should be used for sizing viruses by subsequent filtration through smaller pores. The determination of virus size would then be based on the major population of particles in the virus suspension. In the past, as little as 0.1 to 0.001% of the initial virus population was the basis for size determination, because more than 99.9% of the virus was often lost by adsorption to membranes during the clarifying procedures.

Virus aggregation as the cause of the non-neutralizable persistent fraction

The non-neutralizable or persistent fraction of virus populations has been found to be caused by aggregated virus. Detailed investigation was performed with the prototype strain of echovirus type 4 (Pesascek), as this virus is notorious for its large non-neutralizable fraction. When Pesascek virus was clarified by low-speed centrifugation, homologous antiserum hardly neutralized the virus. However, when the virus was filtered through membranes having a porosity only twice the diameter of the virus, monodispersed virus was obtained which was efficiently neutralized. Serum titers were up to 1,000 times higher if the neutralization test was carried out with monodispersed virus. Virus in non-neutralizable aggregates was found to constitute 30% of the infective units of unfiltered Pesascek virus but only 0.1% of the antigenically related DuToit strain. This explains why DuToit strain has been a more satisfactory indicator strain for detecting type 4 antibodies, regardless of the echo 4 strain used for inducing the antibodies. Clarified suspensions and ultrafiltrates of viruses belonging to the picorna-, reo-, myxo-, adeno-, herpes-, and poxvirus groups were studied. Clarified suspensions yielded persistent fractions of 0.005% for poliovirus, of 0.1% for reovirus, of 0.6% for influenza virus, of <0.001% for adenovirus, of 0.06% for herpesvirus, and of 10 to 30% for vaccinia virus. In all cases the persistent fractions were removed by membrane filters which had a pore diameter no larger than twice that of the virus under test, and the high concentration of virus in each ultrafiltrate was completely neutralized by antiserum.

Multiplicity reactivation of vaccinia virus particles treated with nitrogen mustard

The nitrogen mustard bis(beta-chloroethyl)methylamine, a radiomimetic alkylating agent, is known for its ability to inactivate viruses in general and poxvirus in particular. These experiments show that vaccinia virus is rapidly inactivated by it. They show, in addition, that the treated virus exhibits multiplicity reactivation in L cells, closely resembling that experienced with the same virus after exposure to ultraviolet rays. These findings have come from observations of plaque titer, on the one hand, and virus particle aggregation (measured in the electron microscope), on the other. The titer of the treated virus is very sensitive to particle aggregation, increasing and decreasing in a reversible manner as the degree of clumping among the particles is changed. The magnitude of these changes is such that they must be considered in any situation involving plaque assay of the fraction of virus surviving treatment with nitrogen mustard.