A recent study published in the Proceedings of the National Academy of Sciences suggests that using E. coli vaccines on cattle could prevent up to 83 percent of human infections. By combining veterinary, human and molecular data, the authors created a model of the pathogen’s transmission from cattle to humans and used it to estimate the human impact of vaccinating cattle.
The vaccine reduces the level of E. coli in a cow’s feces. But there are some cows that shed a particularly high level of the pathogen, and researchers at the Royal Veterinary College, University of Glasgow and University of Edinburgh say that, although these “supershedders” are relatively uncommon, they’re the main source of E. coli contamination and transmission to people.
“In our data, shedding below [1,000 colony-forming units per gram of] feces was found in 86 percent of samples, but it accounted for less than one percent of the total bacteria shed,” the researchers stated. And the strains most associated with human infections were above 1,300 colony-forming units per gram, they added. “In our simulations, eliminating just the 12 percent highest shedding densities produces a 50 percent drop in the frequency of shedding in cattle, but an 83 percent drop in human cases.”
Previously, there have been studies of the vaccine’s efficacy in animals. David Renter, an epidemiologist with Kansas State University, led research published last year that found that the vaccine can reduce E. coli levels by more than 50 percent in most cattle and by 75 percent in supershedders.
“Studies like mine only measure the impact in cattle,” Renter says. “The outcomes that we’re most interested in are ones that make sure fewer people get sick. Those are incredibly costly or sometimes impossible to do, so we need to rely on these modeling studies to pull the data together.”
Epidemiologist and veterinarian Stuart Reid was the senior author on the study from the U.K. Both he and Renter repeat the adage that, “All models are wrong, but some are useful.” In an email to Food Safety News, Reid acknowledged that the study was based specifically on the Scottish farming environment, and that the benefits of vaccinating cattle may vary from country to country. However, the team “thought it important to lay out the ecological and biological justification for intervention,” he noted.
There are currently two E. coli O157 vaccines on the market – Canada’s Econiche, which blocks the protein that allows E. coli to colonize in a cow’s gut, and America’s Epitopix SRP, which prevents the pathogen’s iron uptake. Both are under limited licensing in the U.S., but Econiche has been fully licensed in Canada.
Despite its availability, less than five percent of Canada’s market is using Econiche, says Rick Culbert, president of the One Health initiative at the company that makes Econiche. This is probably because farmers currently bear the full cost of vaccination but don’t necessarily see any benefit.
“Unlike a lot of other zoonotic diseases, where both animals and humans contract the disease, with E. coli O157, cattle are an asymptomatic carrier,” Culbert says. “The only reason to vaccinate cattle isn’t to benefit cattle, it’s to reduce the human health risk.”
“We often describe this as a public health vaccine,” says Jennifer Shea, Bioniche’s vice president of communications. “We talk about it being a cattle vaccine, so you automatically think it’s an agriculture issue, but it’s for the good of the public.”
Culbert says that those using their vaccine in Canada tend to be smaller operations that raise, slaughter and sell their own cattle.
“For them, the vaccine is almost a form of liability insurance for them to make sure their brand isn’t implicated with this bacteria,” he noted.
Another Econiche client is a dairy farm that also grows produce and wants to protect it from possible contamination through manure or irrigation water. Researchers have also pointed out the possible impact in terms of exposure at petting zoos or simply living and working in rural areas.
Microbiologist Michele Jay-Russell studies foodborne pathogens, and, although she doesn’t work directly with beef, she is interested in how the vaccine could impact E. coli’s environmental dissemination into irrigation water and onto produce.
“Among all the pre-harvest interventions – like grass vs. grain-fed or pasture vs. feedlot – it’s the one that has the most promise,” she says.
Renter agrees. “It would be difficult to show directly how [the vaccine] impacts all those things, but it just makes a lot of sense,” he says. “If you reduce the level in cattle, you’re going to reduce the impacts through a variety of potential human exposures.”
Getting E. coli vaccines to be used more broadly would probably take some kind of government or industry intervention, but no one can predict the specifics beyond that.
“Whether you consume beef or not, you benefit from any cattle being vaccinated,” Culber says. “About a third of the people who get ill from E. coli are associated with the consumption of contaminated beef, about a third are associated with contaminated produce, and the other third is associated with everything from contaminated water to direct contact to crop contamination.”
That’s important to remember because, he says, “If you try to push this on the beef industry, they’re only associated with a third of the illness.”© Food Safety News