A new study suggests cattle vaccines, such as 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 lifelong 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.