Important factors for testing barrier materials with surrogate viruses

Systematic review of the literature on viral persistence and sexual transmission from recovered Ebola survivors: evidence and recommendations

OBJECTIVE

The main aim of this article is to present a comprehensive, systematic review on evidence of sexual transmission from Ebola survivors and persistence of Ebola virus in body fluids of relevance to sexual transmission, and additionally to review condom effectiveness against sexual transmission of Ebola.

DESIGN

We performed a systematic review of viral persistence in body fluids of relevance to sexual transmission of Ebola survivors and evidence of sexual transmission of Ebola, and carried out a targeted review of condom effectiveness.

RESULTS

We identified nine published original articles presenting results on persistence of Ebola virus in relevant body fluids, or reporting suspect sexual transmission from Ebola survivors. We also included unpublished reports from the current 2014/2015 Ebola epidemic in West Africa. We found no articles reporting on condom effectiveness, but have included a targeted review on general condom efficacy and effectiveness.

CONCLUSIONS

We conclude that the risk of sexual transmission from people who have recovered from Ebola cannot be ruled out. We found the longest duration of persistent Ebola RNA in a relevant body fluid from a survivor, to be reported from a man in Sierra Leone who had reverse transcriptase PCR (RT-PCR) positive semen 284 days after symptom onset. In line with current WHO recommendations. We recommend that men are offered the possibility to test their semen regularly for presence of Ebola RNA from 3 months post-symptom onset. Safe sex practices including sexual abstinence, or else condom use, are recommended by WHO until semen has tested negative twice, or in absence of testing for at least 6 months post-symptom onset. Based on evidence reviewed, we conclude that male and female latex condoms offer some protection against EBOV compared to no condom use. Survivors should be offered access to care and prevention, in order to provide them with possibilities to mitigate any risks that may occur, and efforts should be linked to destigmatising activities.

Isoelectric point is an inadequate descriptor of MS2, Phi X 174 and PRD1 phages adhesion on abiotic surfaces

MS2, Phi X 174 and PRD1 bacteriophages are commonly used as surrogates to evaluate pathogenic virus behavior in natural aquatic media. The interfacial properties of these model soft bioparticles are herein discussed in connection with their propensities to adhere onto abiotic surfaces that differ in terms of surface charges and hydrophobicities. The phages considered in this work exhibit distinct multilayered surface structures and their electrostatic charges are evaluated from the dependence of their electrophoretic mobilities on electrolyte concentration at neutral pH on the basis of electrokinetic theory for soft (bio)particles. The charges of the viruses probed by electrokinetics vary according to the sequence Phi X 174⩽PRD1≪MS2, where '<' stands for 'less charged than'. The hydrophobic/hydrophilic balances of the phages are further derived from their adhesions onto model hydrophobic and hydrophilic self-assembled mono-layers. The corresponding results lead to the following hydrophobicity sequence Phi X 174≪MS2<PRD1 where '<' means 'less hydrophobic than'. The respective electrostatic and hydrophobic/hydrophilic features of the phages are further shown to be consistent with their measured adhesions onto polyethersulfone-based membranes with distinct hydrophobicities and charge levels. The methodology clearly demonstrates that the traditionally adopted phage isoelectric point as a relevant physicochemical descriptor for phage adhesion is not adequate for MS2, Phi X 174 and PRD1 bacteriophages.

Methods for the recovery of a model virus from healthcare personal protective equipment

AIMS

To develop methods for recovering a model virus (bacteriophage MS2) from healthcare personal protective equipment (PPE).

METHODS AND RESULTS

Nine eluents were evaluated for recovery of infectious MS2 from PPE: 1.5% beef extract (BE) pH 7.5 with and without 0.1% Tween 80, 1.5% BE pH 9.0 with and without 0.1% Tween 80, 3% BE pH 7.5 with and without 0.1% Tween 80, 3% BE pH 9.0 with and without 0.1% Tween 80 and PBS with 0.1% Tween 80. Methods were applied to experimentally contaminated PPE. Elution followed by two-step enrichment assay could recover virus inputs as low as 1.5 log(10), and could recover >90% of inoculated virus from used items of experimentally contaminated PPE worn by human volunteers.

CONCLUSIONS

BE was effective for recovering infectious viruses from a range of PPE materials.

SIGNIFICANCE AND IMPACT OF THE STUDY

PPE plays a crucial role in interrupting transmission of infectious agents from patients to healthcare workers (HCWs). The fate of micro-organisms when PPE is removed and disposed of has important consequences for infection control. Methods described here can be used to conduct rigorous studies of viral survival and transfer on PPE for risk assessments in infection control and HCW protection.

Aggregation and surface properties of F-specific RNA phages: implication for membrane filtration processes

We report an experimental investigation of the electrokinetic properties and size variations of four F-specific bacteriophages of the types MS2, GA, Qbeta and SP (21-30 nm in diameter) over a broad range of pH values (1.5-7.5) and NaNO3 electrolyte concentrations (1-100 mM). The results obtained by dynamic light scattering show that the aggregation of SP and GA particles takes place over the whole range of pH and ionic strength conditions examined. For MS2 phages, the aggregation of MS2 particles is not observed for pH higher than the isoelectric point (pI) and large ionic strengths for which interparticular repulsive electrostatic interactions are however expected to be sufficiently screened. Aggregation of the MS2 phages, dispersed in 1 and 100 mM electrolyte concentration, occurs at pH 4, which basically corresponds to the pI as determined by electrophoresis measurements. The Qbeta particles suspended in solutions of low electrolyte concentrations aggregate at low pH values (pI approximately 3) and, unlike MS2, at large ionic strengths over the whole range of pH conditions considered in this study. These elements allow the determination of the hydrophobic sequence for the four phages SP approximately GA>Qbeta>MS2. Close inspection of the electrokinetic results reveals small to significant variations of the pI values-depending on the phage considered-with respect to the concentration of indifferent NaNO3 electrolyte. This indicates that features other than chemical and electrostatic in nature play a key role in determining the pI and more generally the electrophoretic mobility mu of viral particles. A qualitative interpretation is given and is based on the consideration of inner electro-osmotic flow within the isolated or aggregated particles. The impact of the flow properties within the particles is further in agreement with recent theoretical formalism developed for the electrokinetics of soft multiplayer particles, the phages analyzed here being some illustrative examples. The determination and qualitative interpretation of the surface properties of the viral particles as reported in the current study are commented within the context of water treatment especially concerning viral removal by membrane filtration processes.

Integrity of powdered and powder-free latex examination gloves

OBJECTIVES

The difference in permeability between one brand of powdered and another of powder-free latex examination gloves was evaluated to determine leak rates.

METHODS

Thirty-one of each type of glove were tested for each of three different conditions: usage by dental personnel (1) for 15 minutes or longer, (2) for less than 15 minutes, and (3) directly from the manufacturer's packaging (zero usage time). Each glove was evaluated in the fingers and the palm. The phiX-174 viral solution in the glove was allowed to penetrate for 15 minutes. Powder (cornstarch) was subsequently added to 20 powder-free gloves, and 15 of these were pierced with a 30-gauge needle.

RESULTS

Powdered gloves showed no leakage rates. Because of this, 30-, 27-, and 25-gauge needles were used to pierce five gloves each. One glove with 27- and 25-gauge needle holes showed leakage. Leakage rates for powder-free gloves: 45.1 percent for more than 15 minutes of use, 25.8 percent for less than 15 minutes of use, and 16.1 percent for zero minutes of use. Two of the 20 pierced and one of the five unpierced powder-free gloves with added cornstarch leaked.

CONCLUSION

Significant differences in leak results between powdered and powder-free gloves suggest further study is needed.

Characterization of virus adsorption by using DEAE-sepharose and octyl-sepharoser

Viruses were characterized by their adsorption to DEAE-Sepharose or by their elution from octyl-Sepharose by using buffered solutions of sodium chloride with different ionic strengths. Viruses whose adsorption to DEAE-Sepharose was reduced most rapidly by an increase in the sodium chloride concentration were considered to have the weakest electrostatic interactions with the solids; these viruses included MS2, E1, and phiX174. Viruses whose adsorption to DEAE-Sepharose was reduced least rapidly were considered to have the strongest electrostatic interactions with the column; these viruses included P1, T4, T2, and E5. All of the viruses studied adsorbed to octyl-Sepharose in the presence of 4 M NaCl. Viruses that were eluted most rapidly following a decrease in the concentration of NaCl were considered to have the weakest hydrophobic interactions with the column; these viruses included phiX174, CB4, and E1. Viruses that were eluted least rapidly from the columns after the NaCl concentration was decreased were considered to have the strongest hydrophobic interactions with the column; these viruses included f2, MS2, and E5.

Viral impermeability of hypoallergenic, low protein, guayule latex films

Guayule latex proteins do not cross-react with antibodies raised against latex proteins in commercially available products manufactured from Hevea brasiliensis latex. Thus guayule latex is a promising raw material for the manufacture of hypoallergenic latex products, safe for use by people suffering from IgE-mediated Type I "latex allergy." Also, guayule latex is a low protein material and therefore unlikely to cause widespread sensitization. Latex products commonly are used as essential barriers against the transmission of disease, and so guayule hypoallergenic latex medical products would be a viable alternative only if they possess effective viral barrier properties. To address this question, fingers of prototype hand-dipped guayule latex examination gloves were tested for their permeability to a surrogate challenge virus, varphiX174. This virus has a diameter of 27 nm and is similar in size to the smallest human pathogenic viruses. Prototype guayule latex condom films were tested using synthetic blood over a range of pressures and, after 4 years of storage, with synthetic blood and with the varphiX174 virus. We concluded that guayule latex films taken from prototype hand-dipped gloves and condoms provide effective barriers to virus transmission and that they remain effective (at least in condoms) after long-term storage.

Virus passage through track-etch membranes modified by salinity and a nonionic surfactant

Why do viruses sometimes not pass through larger pores in track-etch filters? Increasing the salinity (0.8 to 160 mM Na+) decreased phiX174 and PRD1 passage through track-etch polycarbonate membranes (sodium dodecyl sulfate coated but not polyvinylpyrrolidone coated) and PRD1 passage through polyester membranes. Undiminished passage when 0.1% Tween 80 was added implied that nonionic virus adsorption occurred and indicated that high levels of salinity decreased virus passage by decreasing electrostatic repulsion that prevented adsorption.

Implications of laboratory tests of condom integrity

BACKGROUND

There is sufficient evidence from Food and Drug Administration laboratory experiments and clinical studies to draw conclusions about the relative importance of holes and breakage to condoms. The laboratory test methods determined penetration of viruses or virus-size microspheres through holes in condoms under conditions that simulated or exaggerated those expected in actual use, and determined the frequency with which condoms might pass virus or microspheres and the amounts of passage in each case.

GOALS

To summarize and comment on the significance of test results on latex, polyurethane, and natural membrane condoms as barriers to virus passage.

STUDY DESIGN

Published and unpublished data addressing three distinct concerns were analyzed: (1) passage of virus or microspheres through small holes or pores inherent in the material of "intact" condoms which are undetectable by the standard water leak quality assurance test, (2) passage of virus or microspheres through larger holes in "leaker" condoms detectable by the water leak test but marketed because of the finite acceptable quality level (AQL) of the test, and (3) passage of virus through condoms that break during use.

RESULTS

Extrapolating to the passage of semen expected during actual use allowed an analysis of the relative importance of breakage and water-leak-detectable or water-leak-undetectable holes.

CONCLUSIONS

The relative importance of breaks and holes is related to the volume of semen that contains an "infectious dose" of a sexually transmitted disease (STD). When 0.1 mL to 1.0 mL exposures to semen are necessary for disease transmission, the risk during latex condom use primarily results not from holes, but from breakage of condoms. For smaller volumes of semen exposure (0.00001 mL and less), the presence of holes can be as important as breaks. The same qualitative argument pertains to a comparison of "leaker" condoms to the large majority of "intact" condoms.

An in vitro evaluation of condoms as barriers to a small virus

BACKGROUND

Because of the possible presence of small holes, the effectiveness of condoms as barriers to virus transmission is controversial.

GOALS

To determine the proportion of condoms that allow virus penetration and the amounts of virus that penetrate.

STUDY DESIGN

A sensitive, static test was used to evaluate different condom types as barriers to a small virus, including brand with or without lubrication and ones of different materials. The test included some physiologic-based parameters and some parameters that exaggerated expected actual use conditions.

RESULTS

Under test conditions, 2.6% (12 of 470) of the latex condoms allowed some virus penetration; the median level of penetration was 7 x 10(-4) ml. Lubricated condoms performed similarly to nonlubricated ones. Polyurethane condoms yielded results higher than but not statistically different from those for latex condoms.

CONCLUSIONS

Few condoms allowed any virus penetration. The median amount of penetration for latex condoms when extrapolated to expected actual use conditions was 1 x 10(-5) ml (volume of semen). Thus, even for the few condoms that do allow virus penetration, the typical level of exposure to semen would be several orders of magnitude lower than for no condom at all.

Elution of viruses by ionic and nonionic surfactants

The ionic and nonionic surfactants sodium dodecyl sulfate and Triton X-100, respectively, eluted two viruses, phi X174 and PRD1, which were adsorbed to the ionic and nonionic binding membranes cationic polysulfone and nitrocellulose, respectively. Results indicated that complete elution was readily achieved only when combinations of surfactants and binding membranes were matched (i.e., ionic-ionic or nonionic-nonionic).

The removal of phages T1 and PP7, and poliovirus from fluids with hollow-fiber ultrafilters with molecular weight cut-offs of 50,000, 13,000, and 6000

We tested the ability of hollow-fiber ultrafilters with molecular weight cut-offs (MWCOs) of 50,000, 13,000, and 6000 to remove and detect viral agents (phage T1, 50-150 nm; phage PP7, poliovirus, 28-30 nm) from ultrapure water, 0.85% saline with 1% trypticase soy broth, and Dulbecco's modified Eagle minimum essential medium with 10% fetal bovine serum (DMEM-10). Virus diluted in saline and DMEM-10 were tested to evaluate filter performance under conditions that minimize the adsorption of viral particles to the filter matrix. During filtration, the retentate was returned to the input reservoir, and the permeate was removed to a separate vessel. Thus, the virus concentration in the feed increased over the course of filtration. Filter performance was evaluated by comparing the concentration of infectious virus in the initial virus suspension with the virus concentration in the permeate and retentate. Very efficient removal of phages T1 and PP7 was observed with the filters with MWCOs of 13,000 and 6000 (titer reduction > 7 logs) for all three fluids tested. No poliovirus was detected in the permeate of the ultrafilters with MWCOs of 13,000 or 6000 (titer reduction > 6 logs). These results indicate that the ultrafilters with MWCOs of 13,000 and 6000 were very effective in removing small viral particles (25-30 nm) by size exclusion. The recovery efficiency of the virus in the retentate varied by fluid type. However, filtration with virus diluted in DMEM-10 resulted in consistent recovery of the viruses tested. The results suggest that these ultrafilters may have the dual potential of removing viral contaminants from fluids and concentrating virus in the retentate.

Minimized virus binding for tests of barrier materials

Viruses are used to test the barrier properties of materials. Binding of virus particles during passage through holes in the material may yield misleading test results. The choices of challenge virus and suspending medium may be important for minimizing confounding effects that might arise from such binding. In this study, different surrogate viruses, as well as different support media, were evaluated to determine optimal test parameters. Two membranes with high-binding properties (nitrocellulose and cationic polysulfone) were used as filters to compare binding activities of different surrogate challenge viruses (MS2, phi X174, T7, PRD1, and phi 6) in different media. The media consisted of buffered saline with surfactants, serum, or culture broth as additives. In addition, elution rates of viruses that bound to the membranes were determined. The results suggest that viruses can bind by hydrophobic and electrostatic interactions, with phi X174 displaying the lowest level of binding by either process. The nonionic detergents Triton X-100 and Tween 80 (0.1%) equally minimized hydrophobic interactions. Neither anionic nor cationic surfactants were as effective at nontoxic levels. Serum was effective at reducing both hydrophobic and electrostatic binding, with 2% being sufficient for eliminating binding under our test conditions. Thus, phi X174 remains the best choice as a surrogate virus to test barrier materials, and Triton X-100 (0.1%) remains a good choice for reducing hydrophobic binding. In addition, binding of viruses by barrier materials is unlikely to prevent passage of blood-borne pathogens.

Viral leakage risk differences in latex condoms

Through use of a new bacteriophage assay capable of detecting a single viral plaque-forming unit (PFU), viral leakage through multiple replicates of several types of latex condoms has been evaluated. Stocks were used that had been preserved from a previous large study in which viral leakage had been assessed preliminarily in several brands. In the present research, much larger numbers of replicates--on the order of magnitude of 100 condoms per brand--were used. Leakage was demonstrated in single production lots of each of seven brands of condoms. With one notable exception, percent leakage ranged from 0.9 to 22.8%; 100% of the specimens of one profoundly flawed brand leaked. All test condoms were subjected to conditions intended to model these prevailing during coitus. Because the condoms used in this study were aged, current stocks of two widely sold brands were tested for comparison. Of these, 11.8% of one brand leaked, 25.7% of the other. The relevance of the results, which gave a high, albeit physiologically appropriate, challenge to the test brands, is discussed--so too is the significance to condom users of results deriving from a leakage assay of exquisitely high sensitivity.

Virus inactivation by copper or iron ions alone and in the presence of peroxide

Cupric and ferric ions were able to inactivate five enveloped or nonenveloped, single- or double-stranded DNA or RNA viruses. The virucidal effect of these metals was enhanced by the addition of peroxide, particularly for copper(II). Under the conditions of our test, mixtures of copper(II) ions and peroxide were more efficient than glutaraldehyde in inactivating phi X174, T7, phi 6, Junin, and herpes simplex viruses. The substances described here should be able to inactivate most, if not all, viruses that have been found contaminating medical devices.

A simple method to test condoms for penetration by viruses

A method by which virus penetration through condoms can be tested with simple, inexpensive equipment is described. The method uses chi X174 bacteriophage as the challenge virus and physiologically relevant pressure. Penetration by 0.1 microliters (or less) of challenge suspension can be readily detected. As examples, latex and natural-membrane condoms were examined.

Filtration sizes of human immunodeficiency virus type 1 and surrogate viruses used to test barrier materials

Filters with well-defined holes were used to determine the effective diameters in buffer of human immunodeficiency virus type 1, herpes simplex virus type 1, and four bacteriophages (phi X174, T7, PRD1, and phi 6), which may serve as surrogate viruses for testing barrier materials. Bacteriophages phi 6 and PRD1 most closely model human immunodeficiency virus type 1 in filtration size.