December 22, 2021

New study looking at wild birds’ effect on food safety

Several researchers have studied wild bird species, their proximity to cattle operations and how they relate to foodborne outbreaks in the Western U.S.

But little work of this type has been conducted in the Southeastern U.S., where bird species, climate, landscape and livestock operations differ.

Through her project, “Understanding and predicting food safety risks posed by wild birds,” Nikki Shariat, Ph.D., with the University of Georgia, hopes to give Southeastern producers a science-based picture of the risks posed by wild birds. As part of the research, she also plans to collect data on how Salmonella and/or Campylobacter found in bird feces might be influenced by nearby beef and poultry operations and other landscape factors.

The project will include a grower survey asking about their bird control strategies, which ones work and which ones don’t. In the end, the research results will be shared with Southeastern producers through extension meetings, informational sheets and other media.

“One hope is we can update the GAPs (good agricultural practices) that are associated with wild birds,” Shariat said. “A lot of that will come from the computer modeling. What is the risk posed on farm X if farm X is next to some livestock production? We expect that we might see some patterns linked to the bird species as well.

“It should also help us understand what bird control strategies work. It’s not only sharing the results but also thinking about the different types of bird control.”

Joining Shariat are co-principal investigators William E. Snyder, Ph.D., and Laurel Dunn, Ph.D., both with UGA. Snyder is an ecologist formerly with Washington State University, where he studied the presence of foodborne pathogens in West Coast bird species.

Dunn, who Shariat described as an “Extension specialist extraordinaire,” brings a multitude of industry connections throughout the Southeast. A recent addition to the project is Sonia Hernandez, Ph.D., from UGA, who specializes in wildlife diseases.

So far, UGA graduate students Sophia Varriano and Jared Smith have made about 45 visits to roughly three dozen individual farms in Florida, Georgia, South Carolina and Tennessee. The cooperating operations grow several crops, including tomatoes, peppers, squash, eggplant and/or cucumbers.

The visits are in the morning when birds are most active. On each farm, Varriano stands at four different points and counts the number of birds, including those flying over, and the different bird species. 

Smith meanwhile walks up and down the rows looking for bird feces on plants. If he finds a fecal sample, he collects it for lab analysis. He also swabs any fruit below the bird feces as well as swabbing up to two plants within 5 feet downwind. They also note landscape features, such as hedgerows or woods, next to each farm.

The lab analysis is actually two-fold. The first, which Shariat described as low-resolution, involves looking at the different Salmonella serotypes found in each sample.

“We know that certain serotypes are associated with different production systems or the environment,” she said.

Campylobacter is more difficult to assay in a laboratory. Several different species may exist in one sample, so the researchers have to identify each Campylobacter species. 

“Some species have a greater association with different animals,” Shariat said. They then use molecular analysis of the feces itself to identify the bird species so that her team can correlate pathogen presence or absence with particular species. 

This work is then followed by higher-resolution analyses. 

“Our work will use new sequencing-based technologies to identify whether complex populations of different Campylobacter species or of different Salmonella serotypes exist in the same fecal sample.”

Identified isolates will then undergo whole genome sequencing. This allows the researchers to investigate whether there are any connections between Salmonella or Campylobacter found in animal production systems or human outbreaks to those found in the bird feces. 

Although lab analysis is ongoing, she said they have yet to find any Salmonella or Campylobacter in swabs taken from fruit below bird feces or downwind from feces. “This preliminary data is exciting,” Shariat said. “It shows that on-farm transmission doesn’t occur very frequently.” 

The team looks forward to sampling in year 2 of the study to see if these trends hold true.

The results of the farm surveys as well as the laboratory testing will be used to create a computer risk model. Together with results of the grower survey, Shariat said they plan to produce science-based wild bird risk-management materials for producers that will be shared through extension programs.

— The Center for Produce Safety

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