Science & Environment

'Cold plasma' kills off norovirus

Cold plasma treating almonds
Image caption Cold plasma consists of ionised gas molecules at room temperature

Norovirus, the most common cause of gastroenteritis in the world, can be killed with "cold plasma," researchers in Germany have reported.

The virus, which elicits vomiting and diarrhoea, has gained international notoriety for causing outbreaks on cruise ships.

However, such incidents represent merely a fraction of the tens of millions of cases that occur around the world each year.

The research appears in mBio journal.

Preventing norovirus outbreaks is complicated by the fact that the virus is highly resistant to several different chemical disinfectants.

Bleach, a chlorine-based solution, is currently the most effective treatment, but researchers are seeking more convenient alternatives.

One such alternative is cold plasma, also known as non-thermal plasma. This "fourth state of matter" consists of ionised gas molecules at room temperature. These ions can destroy many kinds of microbes, but their effect on viruses was less clear.

Handheld gadget

A team of scientists led by Dr Birte Ahlfeld and Prof G√ľnter Klein at the University of Veterinary Medicine in Hannover examined the effect of cold plasma on a strain of norovirus isolated from a human faecal sample taken during an outbreak at a military base in Germany.

Cold plasma treatment led to a roughly 20- to 50-fold reduction in the number of virus particles.

The viruses were destroyed because cold plasma consists of highly noxious ions, called reactive nitrogen and oxygen species, which exhibit potent antimicrobial activity.

Moreover, the cold plasma generator, which produces the ions by applying an electric field to ambient air, could be designed as a handheld device. Alternatively, commonly contaminated surfaces, such as salad bars, could have cold plasma generators built into them.

Image caption Norovirus is infamous for causing gastroenteritis outbreaks on cruise ships

"A spread of norovirus can be inhibited at crucial points, which as we know from our previous studies are all surfaces with frequent contact to human skin or hands," Dr Klein said.

"Handheld devices can be used to disinfect different surfaces or a plasma box for hands or cutlery or plates is possible."

Growing problem

Other researchers shared Dr Klein's enthusiasm.

Brendan Niemira and Dr David Kingsley, food safety experts at the US Department of Agriculture who were not involved with the research, said: "Cold plasma is a waterless technology, so there wouldn't be any solutions to apply or to rinse off.

"That reduces water usage throughout the process, and might be more advantageous for continuous cleaning applications, such as for conveyor belts, materials handling surfaces, etc."

A further advantage, they noted, is that storage of large volumes of sanitiser on site would no longer be necessary.

Mr Niemira and Dr Kingsley believe that treating surfaces with a combination of bleach and cold plasma may eventually become the gold standard of norovirus decontamination.

Over the decades, norovirus research has been greatly hindered by the inability to grow the virus in the laboratory. However, in late 2014, scientists at the University of Florida reported a breakthrough after they successfully cultured the virus in a complex in vitro system that utilised B-cells.

Besides decontaminating surfaces, cold plasma may have other medical applications. For instance, its use in treating dental caries has recently completed phase II clinical trials in the United States.

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