European and World Health Organization scientists say a deadly outbreak of E. coli bacteria that has killed 18 people is a rare and virulent strain of the bacteria. The latest victim died Wednesday night in Germany.

The United Nations agency said Thursday that preliminary genetic tests suggest the highly infectious strain is a mutant of two different E. coli bacteria. A food safety expert at the WHO, Hilde Kruse, said the strain has various characteristics that make it more virulent and toxin-producing than other strains.

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. Hundreds have been hospitalized and several of them are in intensive care.

Health officials have been unable to find the cause or origin of the outbreak, but similar infections come primarily from contaminated foods.

With the uncertainty surrounding the latest outbreak, concern about European produce is spreading. The United Arab Emirates on Thursday banned the import of cucumbers from Spain, Germany, Denmark and the Netherlands.

Russia said it is banning the import of all fresh vegetables from the European Union — an action the EU immediately called “disproportionate.” The EU, which exported $853 million worth of vegetables to Russia last year, said it would seek an explanation from Moscow.

Russia said vegetables already imported from EU countries will be seized. The chief of Russia's consumer protection agency, Gennady Onishchenko, urged his countrymen to avoid imported vegetables in favor of domestic products.

Germany initially pointed to cucumbers from Spain as a possible source of the contamination, but further tests showed that those vegetables were not the cause of the outbreak.

The erroneous conclusion angered Spanish officials. Prime Minister Jose Luis Rodriguez Zapatero said Spain will seek reparations from authorities in Europe for the damages its vegetable growers have suffered.

Germany's national disease center says the outbreak started nearly two weeks before the first infections were reported in mid-May. The infection can result in a secondary disease that attacks the victims' kidneys, sometimes causing seizures, strokes, comas and death.

The European Centre for Disease Prevention and Control said Thursday that the outbreak of the current strain of bacteria has been rarely reported worldwide. It recommended hygiene and cooking foods thoroughly to prevent infection.

Vegetable growers across Europe say they are suffering major economic losses as the mystery goes unsolved. Spain says it is losing $288 million a week because of import bans and weak demand for the produce, while the Netherlands says it is losing $43 million.

The president of Spain's produce export trade group said almost all Europeans have stopped buying Spanish vegetables and fruit.

The World Health Organization said Thursday that it does not recommend any trade restrictions related to the outbreak.