TORONTO - A new study suggests cattle vaccines like one developed in Canada could slash the number of human infections with dangerous E. coli O157 bacteria.
The researchers say that human cases could be reduced by nearly 85 per cent if the vaccines were used on cattle, which are the main source of the bacteria.
Canadian researchers developed an E. coli vaccine for cows a number of years ago; it was approved for use in this country in 2008.
But the vaccine isn't commonly given because cattle farmers have no incentive to spend the $6 a head to vaccinate their cows.
E. coli O157 does not sicken cattle, so the vaccine doesn't protect the animals, but rather the people who consume meat from them.
E. coli O157 was responsible for the large Walkerton, Ont., outbreak in 2000 and was behind last year's XL Foods meat recall, the largest in Canada's history.
Infection with E. coli O157 can be fatal; seven people died as a result of drinking E. coli-contaminated water in Walkerton. Survivors can sustain life-long kidney damage, and it is a major cause of acute kidney failure in children.
The new study is from scientists in Britain and was published Monday in the journal Proceedings of the National Academy of Sciences, or PNAS.
The researchers used modelling techniques to assess E. coli O157's transmission risks from cattle to people, determining that cows that are so-called supershedders drive the spillover of bacteria into humans.
Cattle vaccines effectively halve the frequency of shedding of the bacteria, the authors say. But because of the role played by supershedders, the human benefit of vaccine use in cows should be "substantially greater than anticipated from the observed efficacy," and could be underestimated by those who don't take the supershedder effect into consideration, they write.
"Specifically, we show that vaccines producing a 50 per cent reduction in shedding frequency in cattle (consistent with reported efficacies) could reduce human cases by nearly 85 per cent. We conclude that vaccination of cattle, the major reservoir for E. coli O157, could be an especially effective public health control against a serious disease."
Dr. Stuart Reid, senior author of the paper and principal of the Royal Veterinary College in London, says outbreaks like the one at Walkerton garner a lot of headlines, but there are also sporadic cases that contribute to the societal costs of E. coli O157 infections in people.
"This is an organism that when it hits an individual, particularly if it's a young individual, can have profound effects. So it's one we have to take seriously," he said in an interview.
"You don't need 20 of those (cases) to sit up and take notice. When you've seen one kid on dialysis, that's sufficient."
Dr. Brett Finlay, a University of British Columbia researcher who led the team that developed the Canadian vaccine — marketed as Econiche by Bioniche Life Sciences Inc. — maintains that the cost of vaccinating all cattle in Canada would be more than recouped by the reduction in health-care costs accrued in caring for people who become infected.
In an opinion page article Finlay wrote for the Vancouver Sun during the XL Meat beef recall, he said vaccinating Canada's entire herd would cost about $50 million, about one-quarter of what is spent annually in Canada to care for people sickened by the bacteria. That estimate — $200 million a year — does not include costs associated with beef recalls.
"There will always be O157 in beef until the vaccine is adopted and no amount of inspectors will detect all O157," Finlay wrote.
But the British study acknowledges that questions remain about who should absorb the cost of vaccinating cattle. Reid says some of his co-authors are currently working on a cost-benefit analysis of the vaccine.