Backyard chickens that people keep for eggs and as pets may also offer humans other, less savory bounty—bacteria that can cause diarrhea, cramping, abdominal pain, and potentially fatal infections, a Finnish study suggests.
Researchers swabbed the bottoms of 457 birds living on 50 backyard chicken farms in Finland and also tested boot socks from their human owners. They often found the bacteria Campylobacter jejuni and Listeria monocytogenes, both of which can transmit bothersome as well as potentially more serious infections to humans.
“Most commonly, the bacteria found from these chickens can cause transient self-limiting gastrointestinal symptoms, but rarely they can also cause life-threatening infections,” lead study author Leena Pohjola of the University of Helsinki said by email.
The good news is, researchers didn’t find much evidence of Salmonella enterica, a common source of food poisoning often traced back to chicken and eggs, or of Yersinia pseudotuberculosis, another bearer of foodborne illness that can come from chickens.
People may also take some comfort in another fact: The bacteria researchers did detect have nothing to do with bird flu, which is a virus that can be transmitted to people who come in contact with wild or domestic bird feces or other secretions and most of the time causes no symptoms.
Backyard poultry has become increasingly popular in industrialized countries, and a growing number of urban farmers keep the birds as pets and a source of eggs, researchers note online January 11 in the journal Zoonoses and Public Health.
To see how these human-bird interactions may transmit diseases to people, researchers tested birds residing in flocks of 500 or less residing in yards across Finland in 2012 and 2013. Most of the flocks had fewer than 50 chickens.
They collected cloacal swabs, which are taken from the posterior opening of a bird’s digestive, urinary, and reproductive tracts. Located under the tail and covered by feathers, this is the part of the chicken that expels both feces and eggs.
Almost half of the farms had chickens that tested positive for Campylobacter jejuni, and a third had birds with Listeria monocytogenes.
Salmonella enterica and Yersinia pseudotuberculosis were each detected on one farm apiece.
Then, to see how much bacteria people were getting from chickens, researchers tested bird owners’ boot socks once in the winter when the cloacal swabs were done and again in the spring.
Socks were more likely to be contaminated in the winter, when 22 percent of samples were positive for Campylobacter jejuni and 26 percent had evidence of Listeria monocytogenes. Springtime samples had just 5 percent and 14 percent of each bacterial type, respectively.
Some of the bacteria samples tested were strains that won’t respond to antibiotics commonly used to treat resulting infections in humans, the study also found.
While antibiotics aren’t commonly used to prevent disease in chickens on commercial poultry farms in Finland, it’s possible that some people who keep the birds as pets might be more likely to treat chickens with antimicrobials, the researchers note.
One limitation of the study is that it didn’t assess whether humans actually got sick. The findings suggest that Campylobacter jejuni is a potential source of illness in people, but the role of chickens as carriers of Listeria monocytogenes isn’t certain, the authors conclude.
Backyard farmers can protect against disease by wearing gloves to clean chicken coops and regularly washing their hands, said Paul Wigley, an avian infection researcher at the University of Liverpool in the U.K. who wasn’t involved in the study.
Even though people may be tempted to treat their chickens as pets, it’s best for infection prevention to avoid thinking of the birds just like cats or dogs with feathers, Wigley added by email.
“Don’t let the chickens into the house,” Wigley advised.