The World Health Organization says the deadly outbreak of E. coli bacteria that killed 17 Europeans, is a new strain that has never been seen before.The U.N. agency on Thursday said preliminary genetic tests suggest that the strain is a mutant of two different E. coli bacteria with lethal genes.A food safety expert at WHO, Hilde Kruse, said the strain has various characteristics making it more virulent and toxin-producing.More than 1,500 people in nine European countries have been sickened by the rapid spread of the bacteria, with all but one of the deaths and hundreds of the illnesses occurring in Germany.Health officials have been unable to find the cause or origin of the outbreak. With the uncertainty, Russia said it is banning the import of all fresh vegetables from the European Union.The EU, which exported 853 million dollar worth of vegetables to Russia last year, said it would seek an explanation from Moscow.