Florida’s White Ibises May Be Spreading Disease

The increasingly urban birds are carrying salmonella. 

Published December 14, 2016

If you’re golfing in Florida this winter, resist the urge to feed the friendly white ibises congregating around the water hazards—they might just give you salmonella.

The birds, native to Florida’s dwindling wetlands, have been moving to urban golf courses and parks. There they come into close contact with people—even being hand-fed in some cases—and leave their droppings on benches and buildings. Each point of contact has the potential to infect people.

Florida has between 5,000 and 6,000 cases of salmonella poisoning a year. The majority are not associated with food-borne outbreaks, and the most significant sources have yet to be identified. Wild birds are frequent carriers of salmonella bacteria, so Sonia Hernandez, a wildlife disease researcher at the University of Georgia, wondered whether the white ibises might be contributing to the toll.

Hernandez and her colleagues tested the droppings of birds in both urban areas and at nesting sites in the wetlands, and found that 13 percent of adult birds and 35 percent of nestlings carried salmonella—a surprisingly high number given the birds showed no clinical symptoms.

“We didn’t expect to see such a high prevalence in healthy birds,” says Hernandez.

They identified a large number of different strains of salmonella in the ibises, of which almost half matched strains known to affect people. A third of the identified strains were in the top 20 of concern for people in the years in which the study was conducted. Also, the scientists found that the prevalence of salmonella was actually higher in urban birds than those living in the wetlands, and the strains found in urban areas were more likely to be ones that matched human cases.

The researchers suspect that the birds pick up the salmonella bacteria from the soil, water, or other birds’ feces while foraging for food on golf courses or in parks, and pass it on to people through their droppings. While conducting their study, the researchers frequently saw people sitting or leaning on surfaces covered in ibis feces. But the salmonella is not just dangerous to humans. The birds can bring it back to their nesting sites and infect their young, which can cause large-scale die-offs.

With salmonella, Florida is (as in so many other ways) a bit weird. For one thing, there is a lot of salmonella floating around in the environment there, says Lawrence Goodridge, a food safety researcher at McGill University in Montreal, partly because of the types of wildlife; in addition to birds, alligators and turtles can also carry the bacteria. “It’s very easy to find [salmonella], even in water used for irrigation,” says Goodridge.

“And they are strange strains you don’t see elsewhere. A lot of Florida outbreaks are not typical of the rest of the country,” he says.

This makes it hard to determine the source of infection when public health officials are investigating outbreaks. “It’s unlikely that people would think of feeding birds at the park as something they should report to their doctor when they get sick,” says Hernandez. “So these mystery cases are often not well investigated.”

Although food-borne outbreaks are still the biggest cause of human salmonella infections in the United States and Canada, Goodridge says environmental sources will likely become more of a problem in the future.

“Climate and habitat are changing for wild animals, forcing them into new areas, or creating new habitats,” he says. “That can have implications for food safety, especially if those new habitats are close to areas of food production.”