An analysis of studies examining the role wildlife play in the transmission of food-borne illness and antimicrobial resistance in the food chain offers a broad picture of what's known on the topic and identifies gaps in current knowledge.
Published in August in Zoonoses and Public Health, the research analyzed nearly 900 studies dating from the 1990s that looked at wildlife's role in transmitting bacterial pathogens and antimicrobial resistance to the food chain.
Researchers found a significant body of research on the role wild birds play in the transmission of pathogens such as E. coli, salmonella and campylobacter, but found little research on how to actually reduce risks posed by wildlife, said Jeff LeJeune, head of the Food Animal Health Research Program at Ohio State University.
"We scoured the data to find out how much information is actually out there regarding antimicrobial resistance and what role wildlife play in how it's transmitted," said LeJeune, a veterinarian and microbiologist, and one of the study's co-authors. "What we wanted to do is take a look at the data that's already available instead of starting from scratch.
"To do that, you need to systematically look at who's done what and where and when, and not just pick the studies you like or agree with. Then you look at the strengths and weaknesses of those studies, so you can design experiments to fill in the gaps."
The team found that the most frequently investigated wildlife groups were birds at 47%, deer and related mammals at 15%, rodents at 10%, and feral pigs at 9%.
The most frequently studied domestic animals studied were cattle at 25%, poultry at 11%, and swine at 8%.
However, only a handful of studies actually looked at possible interventions to control transmission of food-borne illness to the food chain, LeJeune said.
"Sure, it's always nice to have more data, but we don't really need another prevalence study or more surveillance before we can act," he said. "We need to focus research efforts to determine what interventions will help solve problems that have already been identified."
Manure, pests and contamination process next steps
LeJeune and other researchers at FAHRP hope to shed light on potential mitigation factors in several ongoing projects, including studies on:
• How birds, raccoons and mice are associated with pathogens in dairy and feedlot settings in the U.S. and Canada.
• The survival of pathogens in fields to determine the safety of growing vegetables on land after manure application. Findings could be helpful as the Food and Drug Administration re-examines a proposal that would have mandated a nine-month waiting period between manure application and harvesting of vegetables destined for the fresh produce market, LeJeune said. "It's one thing to make up an answer, but you need data to support sound policy decisions," he said.
• How often tomatoes get contaminated before, during and after harvest. "If we find out that tomatoes are clean on the vine, but contaminated in the box leaving the farm, then we know when we need to intervene to prevent that from happening," LeJeune said. "If they're contaminated on the vine, then we need to intervene upstream. It will show us where we can have the biggest impact with an intervention."
The studies result from a philosophy supporting data-derived decision-making, LeJeune said.
"Surely there's going to be contamination inputs throughout the food chain, but where are the biggest ones? If we can target those, we can have the biggest impact in enhancing the safety of the food chain.
"There could be 100 things and all contribute 1% to the problem. Or maybe there's one that contributes 80% — that's where we want to go. Let's identify the low-hanging fruit."
But before making recommendations, researchers must provide policy-makers with data, LeJeune said.
"You need the data to support your conclusions," he said.
Those conclusions can then be turned into recommendations — recommendations to industry, to consumers, and to public health policymakers, LeJeune said.
"Because without the data, it's just opinion," he said.