Germ sleuths searching for the origins of the bacteria causing a rare and potentially deadly kidney disease in Europe may find it in cows, not cucumbers.
Cattle are the main reservoir for E. coli, the family of bowel-dwelling bacteria from which the new bug comes, said Rowland Cobbold, a veterinary public health researcher at the University of Queensland in Australia. Besides being more virulent and lethal, the strain that emerged in Germany a month ago resists a dozen antibiotics, providing more clues about its origins, he said.
“The cucumber may be the lead back to the original ruminant that was the source,” Cobbold said in an interview from Gatton, Australia. “It’s almost entirely likely that it came from cattle at some point.”
Knowing where and how the germ entered the food chain will enable authorities to control the outbreak, which the World Health Organization said has infected about 1,823 people, killing as many as 18 globally. Tests on cucumbers from Spain, previously thought to be the source of the outbreak, found they’re not responsible, the European Commission said on June 1.
“It’s now a priority to identify the source of the E. coli infection in order to put in place further measures to protect the population,” German government spokesman Steffen Seibert said yesterday.
E. coli bacteria are commonly found in the human gastrointestinal tract, where they usually cause no harm. The German variant, known as O104, is a hybrid of strains carrying genes that can cause bloody diarrhea and a toxin that may lead to a complication known as hemolytic uremic syndrome.
“There’s been a couple of cases of O104 strains before, but nothing as virulent as this,” Cobbold said. “As far as we can tell, it’s an entirely new strain.”
Outbreaks of bloody diarrhea caused by E. coli have usually been linked to contaminated meat, Cobbold said. In more recent outbreaks where fruit and vegetables were implicated, E. coli-contaminated manure or irrigation water were found to be the original source, he said.
“If this goes the same way as previous investigations, they’ll find the ‘smoking gun’ -- the ‘smoking tomato’ or the ‘smoking cucumber’,” Cobbold said. “They will then follow the production source back to the farm and they’ll work out the various contamination roots.”
Most likely that will lead to the “smoking cow,” or at least a specific herd where the strain can be found, he said.
Manure from cattle infected with the microbe can spread in the air and water, potentially contaminating vegetable fields, said James Paton, head of the bacterial pathogenesis laboratory at the University of Adelaide in Australia.
“If you’re trying to grow hydroponic lettuces half a kilometer down the road from a cattle feedlot, even if you don’t have any cattle on your property, there’s the potential for manure dust to blow down on your farm,” Paton said. “It’s easy.”
It highlights the need to prevent fecal material from animals contaminating water that comes into contact with food, especially produce eaten raw, said Peter Collignon, head of infectious diseases at Australia’s Canberra Hospital, who serves on a World Health Organization panel studying antibiotic resistance in the food chain.
“This is a much bigger issue,” Collignon said. “There is a lot of stuff going on all the time that’s just falling below the radar.”
Cow feces were implicated in E. coli-contaminated spinach in a 2006 outbreak in California that killed three people and sickened 200. Food animals and waterways should also be tested to find the source of the current outbreak, Collignon said, adding that the strain’s resistance to certain antibiotics should make it easier to identify.
The German O104 carries genes that enable it to evade a dozen antibiotics, including Sanofi and Abbott Laboratories’ Claforan and other so-called third-generation cephalosporin medicines. It’s possible that antibiotic use, especially in livestock production, helped spawn the new O104 E. coli strain, Cobbold said.
“A question with the O104 outbreak is just how much antimicrobial resistance is an important issue,” he said. “If the bug has come from a country where there is poor antimicrobial regulation, particularly for the third-generation cephalosporins, that may be a contributing factor that may well select for this bug. But it will have come from cattle either way.”
The pattern of drug resistance is a concern to investigators, said Winifred Kern, head of the Centre for Infectious Diseases and Travel Medicine at the University Hospital in Freiburg, Germany, in an e-mailed statement. It “highlights the risks of spread of resistance across human and animal micro-organisms, which could be linked to inappropriate antibiotic use,” she said.
Rates of E. coli bacteria from patient specimens resistant to third-generation cephalosporins in Europe varied from 19 percent in Bulgaria and 17 percent in Italy to 1.8 percent in Iceland and 2.3 percent in Norway, the European Centre for Disease Prevention and Control in Stockholm said in a report in November.
Resistance to the medicine is an increasing problem in animals in the European Union, although there is insufficient data available to properly assess the risk, the European Medicines Agency said in a March 2009 report. Cephalosporins authorized for use in food-producing animals include Pfizer Inc.’s Excede, it said.