The World Health Organisation (WHO) has said the E.coli bacteria responsible for a deadly outbreak that has left 18 dead and sickened hundreds in Europe is a new strain that has never been seen before.
Preliminary genetic sequencing suggests the strain is a mutant form of two different E.coli bacteria, with lethal genes that could explain why the Europe-wide outbreak appears to be so massive and dangerous, the agency said.
Hilde Kruse, a food safety expert at the WHO said: "This is a unique strain that has never been isolated from patients before."
She added that the new strain has "various characteristics that make it more virulent and toxin-producing.
So far, the mutant E.coli strain has sickened more than 1,500 people, including 470 who have developed a rare kidney failure complication, and killed 18, including one overnight in Germany, the country hit hardest by the outbreak.
Researchers have been unable to pinpoint the cause of the illness, which has hit at least nine European countries, and prompted Russia to extend a ban on vegetables to the entire European Union.
Nearly all the sick people either live in Germany or recently travelled there. British officials announced four new cases, including three Britons who recently visited Germany and a German person on holiday in England.
German officials have warned people not to eat lettuce, tomatoes and cucumbers.
Fearful of the outbreak spreading into Russia, the country on Thursday extended its ban on vegetable imports to all of the EU. Russia had banned fresh imports from Spain and Germany on Monday.
The United Arab Emirates issued a temporary ban on cucumbers from Spain, Germany, Denmark and the Netherlands. State news agency WAM said the Gulf nation's Minister of Environment and Water issued the order yesterday based on information "from international food safety agencies and news reports."