Cold plasma touted as treatment to tackle norovirus
Three different dilutions of a human norovirus (NoV) positive stool samples were prepared and treated with CAPP for various lengths of time, up to 15 minutes.
The longer the treatment time the more the number of virus particles in norovirus was reduced; so samples treated for the longest time had the lowest viral load.
CAPP treatment had shown potential in reducing Listeria monocytogenes contamination on pre-packaged ready-to-eat (RTE) foods, according to a study in 2012.
Current disinfection methods
Human norovirus is extremely stable in the environment, showing resistance to detergent-based cleaning and disinfection with chlorine and heating to 65°C, freezing, and acidification.
Disinfection of surfaces in contact with infected humans is said to be critical for the prevention of cross-contamination and further transmission of the virus.
“To date, only the use of sodium hypochlorite as a chemical disinfectant allows a significant inactivation of human NoV strain GII on stainless steel,” said the researchers.
“Because sodium hypochlorite treatment may leave residual chemicals, the effective inactivation of NoV using CAPP seems to be an attractive alternative, particularly in food production and health care settings.”
Inactivation of the virus particles functions is achieved through synergy effects of the cold plasma-initiated air chemistry consisting of nitric oxide (NO) and reactive oxygen species.
The sample used as NoV source was from a 2011 outbreak in a German military facility where 27 fell ill.
Three dilutions of a stool sample from one of those sickened were prepared on sterile petri dishes.
Reduction of virus particles
CAPP reduced potentially infectious virus particles from 22,000 (similar to what would be on a surface touched by someone infected) to 1,400 after 10 minutes, and 500 after 15 minutes.
Some reductions in viral load were seen in one to two minutes of treatment.
“From the initial starting quantity of 2.36 x 104 genomic equivalents/ml, sample exposure to CAPP reduced this value by 1.23 log10 and 1.69 log10 genomic equivalents/ml after 10 and 15 minutes, respectively (P<0.01),” found the study.
“CAPP treatment of surfaces carrying a lower viral load reduced NoV by at least 1 log10 after CAPP exposure for 2 min (P<0.05) and 1 min (P<0.05), respectively.”
NoV viral loads were quantified by quantitative real-time reverse transcription PCR (RT-qPCR).
The assay has limitations as it only detects and quantifies the amount of viral RNA and does not estimate the viability or infectivity of intact viral particles, said the researchers.
However, the use of an RNase pre-treatment helps to control for disrupted viral particles and improves estimations.
A handheld device to disinfect different surfaces and a plasma box for hands is conceivable.
Future studies will test the disinfection properties on additional surfaces and NoV genotypes and examine the virus capsid structure before and after CAPP treatment.
Three of the authors (G. Morfill, Y. Li, and J. L. Zimmermann), who conducted the research while at the Max Planck Society, are now founder members of private company, Terraplasma, which works in cold plasma developments.
Source: mBio (American Society for Microbiology)
Online ahead of print, DOI: 10.1128/mBio.02300-14
“Inactivation of a Foodborne Norovirus Outbreak Strain with Nonthermal Atmospheric Pressure Plasma”
Authors: Ahlfeld B, Li Y, Boulaaba A, Binder A, Schotte U, Zimmermann JL, Morfill G, Klein G.
