Urbanized White Ibises Could Be Transmitting Salmonella to Human Populations

If your patient is showing signs of a Salmonella enterica infection and has recently been to the park to feed the local wildlife, then they may not have food poisoning after all. According to recently-published research conducted by scientists at the University of Georgia (UGA), the Centers for Disease Control and Prevention (CDC), and the Lion Country Safari Park, urbanized white ibises may be shedding Salmonella and could even be transmitting it to people visiting local green spaces.

“White ibises likely become infected with Salmonella from environmental sources, and then…transmit it to people visiting urban parks,” explained Sonia Hernandez, PhD, an associate professor at the UGA Warnell School of Forestry and Natural Resources and the UGA College of Veterinary Medicine, in an article in UGA Today. She added, “People feed ibises in these parks, and the birds form large flocks that drop a lot of feces on picnic tables, benches, and other surfaces.”

CDC educational materials indicate that S. enterica is usually transmitted through consumption of food or water contaminated with animal feces, although it can also occur through direct contact with infected animals—such as turtles—or their environment; it can also be transmitted directly between humans. Although symptoms of S. enterica are similar to food poisoning (acute diarrhea, abdominal pain, fever, and sometimes vomiting) and many patients assume that they have food poisoning when infected, S. enterica is actually a non-foodborne bacterium. However, in the event that a patient has picnicked at a park with a large ibis population, it is very likely that they may have consumed contaminated fecal matter while dining.

From 2010 to 2013, Dr. Hernandez and her team collected fecal samples from white ibises at 17 sites in Palm Beach County, Florida. Two of the sites were located within natural areas, but the other 15 sites were urban parks, zoos, or neighborhoods. In addition, they collected fecal samples from ibis nestlings in two Florida counties; in total, 333 birds were sampled, according to UGA Today. Thirteen percent of the adult birds and 35% of the nestlings were shedding Salmonella, and the rate of shedding decreased as the percentage of wetlands and grasslands around the area increased.

“This suggests that natural ecosystem land cover types support birds with a lower prevalence of infection,” the team noted, adding that open-developed land types such as parks, lawns, and golf courses also had more Salmonella diversity than the more natural areas. The group tested the serotypes of the Salmonella that the ibises carried and discovered that 33% of the infected birds carried strains of Salmonella that infected humans during the years of the study, 2010 to 2013. “44% of the strains of salmonella we found exactly matched strains…that had caused disease in people and which were not associated with food outbreaks,” Dr. Hernandez said.

The team also noted that since urban ibises return to the wild to mate, they can carry infections with them to more isolated areas, thereby increasing the spread of the virus; this could endanger nestlings in less urban areas. They also recommended additional environmental testing and noted that “it is common to see people, especially children and the elderly, leaning or sitting on surfaces contaminated with white ibis feces.” Given that nearly half of Salmonellosis cases each year are children younger than five years of age in whom the infection can have particularly severe health consequences, the researchers noted that in Australia a similar highly urbanized species of ibis is already considered not just a nuisance, but a public health threat.