LONDON (AP) - The World Health Organization said Thursday that the E. coli bacteria responsible for an outbreak that has left 17 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 told The Associated Press that "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 others, including 470 who have developed a rare kidney failure complication. Reasearchers have been unable to pinpoint the cause the outbreak, which has hit at least nine European countries.
Nearly all the sick people either live in Germany or recently traveled there. Two people who were sickened are now in the United States, and both had recently traveled to Hamburg, Germany, where many of the infections occurred.
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.
Lyubov Voropayeva, spokeswoman for the Russian Agency for the Supervision of Consumer Rights, told the AP the ban has been imposed immediately for no definite period of time.
The agency's chief Gennady Onishchenko told Russian news agencies that this "unpopular measure" would be in place until European officials inform Moscow of the cause of the disease and how it is being spread.
"How many more lives of European citizens does it take for European officials to tackle this problem?" he told the state-owned RIA Novosti news agency.
No fatalities or infections have yet been reported in Russia.
Medical authorities appeared late Wednesday no closer to discovering the source of the infection. The outbreak is already considered the third-largest involving E. coli in recent world history, and it may be the deadliest. Twelve people died in a 1996 Japanese outbreak that reportedly sickened more than 12,000, and seven died in a 2000 Canadian outbreak.
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Vasilyeva contributed to this story from Moscow.