The Institute for Environmental Management Technology (IEMT), which is part of the National Institute of Advanced Industrial Science and Technology (AIST), has successfully inactivated norovirus, one of major pathogens causing food poisoning in seafood, and previously designated as small round-structured virus (SRSV), by using micro-bubbles containing low concentration ozone.
If shellfish such as fresh oysters infected with norovirus are eaten, acute gasterointestitis may occur, bringing on symptoms of vomiting, stomach ache, diarrhoea and fever.
Currently the measures available to fight the norovirus include cultivating oysters and other shellfish in sterile seawater, and using chlorine-based germicide. However, the scientists point out that sterile cultivation is costly, and cold seawater in winter season lowers the filtering capability of the oyster, thus hampering effective viral eradication. The norovirus is resistant to chlorine-based germicide and sterilising alcohol, and the use of high chlorine concentration will make shellfish unpalatable. It is this reason that has necessitated the development of an effective method to inactivate the norovirus.
The IEMT/AIST has conducted basic studies on micro-bubble, with the intention of exploring the possibility of its application in engineering. The micro-bubbles are ultra-fine gas water bubbles less than 50 micrometers in size. As they are suspended in water, the bubble size shrinks spontaneously to the level of nanometer, which ultimately helps to dissolve the virus.
The micro-bubbles are characterised by electrical charging and self-pressurising properties, which the researchers suggest will have extensive possibilities for engineering applications. The IEMT/AIST attempted to utilise these effects for making a breakthrough, and successfully inactivated the norovirus by using micro-bubbles of concentrated oxygen containing about 2 per cent ozone. The institute confirmed that the viral inactivation was verified in collaboration with the Tokyo Metropolitan Institute of Public Health (TMIPH).
While the present study effectively inactivated the norovirus suspended in normal water, seawater containing micro-bubbles has good penetrability and is expected to attack not only norovirus in live oysters under cultivation, but also that in unshelled oysters.
The IEMT/AIST says that the next step will be to expand the study further. They have indicated that the technique may also be applicable to suppressing legionella bacteria in a circulating bath system as well as carp herpes virus. The institute added that it had already filed two patents on the back of its studies.