Small water frogs marketed and sold as pets are linked to an outbreak of Salmonella infections from 2008 to 2011, according to the U.S. Centers for Disease Control and Prevention (CDC.
A report published in Pediatrics found that the infection sickened 376 people in 44 U.S. states and sent 29 percent of those to the hospital, mostly children.
"This was the first Salmonella outbreak associated with aquatic frogs, and in this case the frogs are often marketed as good pets for kids," said study leader Sauna Mettee Zarecki.
"The majority of people didn't realize there were any risks from these amphibians or reptiles, like turtles and snakes."
While most people hear about Salmonella-contaminated food, Mettee Zarecki said reptiles and amphibians can also carry the bacteria. Humans can become infected after handling them or coming into contact with contaminated water.
People infected with Salmonella can have prolonged diarrhea, cramps, vomiting and a persistent fever. The infection can be deadly if it's left untreated, and it's most dangerous in the young, the elderly and those with weak immune systems.
Previous research has found that reptiles and amphibians are responsible for about 74,000 Salmonella infections in the United States every year.
In the report, Mettee Zarecki and her colleagues write that researchers from the CDC, along with state and local health departments, investigated an outbreak of Salmonella infections, mostly among children, in 2008.
By early 2009, the number of cases returned to normal before the researchers could find a cause. The investigation was started again when five more children were infected with the same strain of Salmonella in the state of Utah later that year.
To find what was behind the outbreak, the researchers interviewed people who were infected with that strain of Salmonella from January 2008 through September 2011. The asked each person what animals and food they were exposed to in the week before they got sick.
The then compared the data from 18 people with that strain of the bacteria to 29 people who were infected with a different type of Salmonella.
Overall, they found 67 percent of the people in the new outbreak were exposed to frogs during the week before their illness, compared to 3 percent in the comparison group. The majority of people who came in contact with a frog remembered what type - an African dwarf frog/
"Everything really linked these frogs with the illnesses," said Mettee Zarecki.
The investigating eventually led to an African dwarf frog breeding factory in Madera County, California. There, researchers found the same strain of the bacteria in the facility's tank water, tank cleaning equipment, water filters and floor drains.
Though the facility later shut down temporarily for cleaning measures, the researchers warn that the frogs can live for five to 18 years, which means some infected frogs may still be in homes and could continue to cause illness.
"If theses aquariums are in homes, children under five shouldn't be allowed to clean the aquarium," said Mettee Zarecki, adding that this also applies to people with weak immune systems.
"Pets are wonderful. We think they're a great learning tool for children, but some pets just aren't appropriate for children or individuals" with weakened immune systems, she added.