Antibiotic-resistant Salmonella poses a significant public health issue that has grown more prominent in recent years due to the bacteria’s ability to withstand medications. The U.S. Centers for Disease Control and Prevention notes that individuals can contract Salmonella by consuming contaminated foods or through contact with infected people or animals, most often inadvertently through contaminated hands or pet interactions. A study by researchers at Penn State highlights that household dogs are often a neglected source of zoonotic pathogens such as nontyphoidal Salmonella, which can lead to symptoms like diarrhea, fever, and abdominal pain, with some cases leading to severe complications.
The study results have been published online ahead of the upcoming print issue of the journal Zoonoses and Public Health. The research team emphasized that due to the close relationship between dogs and humans, as well as the use of vital antibiotics for pets, household dogs could contribute to the spread of antibiotic-resistant Salmonella. They suggested that increased awareness of the risks, along with proper hygiene practices, could help reduce these cross-species infections.
According to team leader Erika Ganda, assistant professor of food animal microbiomes at Penn State College of Agricultural Sciences, Salmonella infections in dogs can either manifest symptoms or occur without symptoms, with numerous studies showing Salmonella in healthy dogs. A significant concern she noted is the close interaction between humans and pet dogs, which creates favorable conditions for Salmonella transmission from animals to humans, particularly through food contamination and improper handling.
To explore antimicrobial-resistant Salmonella and the zoonotic risk associated with nontyphoidal Salmonella in dogs and humans, the researchers utilized existing biosurveillance systems. They accessed the U.S. Food & Drug Administration’s Veterinary Laboratory Investigation and Response Network to identify nontyphoidal Salmonella strains found in domestic dogs from May 2017 to March 2023.
They then correlated the timing and locations of 87 cases of Salmonella from dogs with strains isolated from humans, using the National Center for Biotechnology Information database, which is maintained by the National Library of Medicine. They discovered 77 potential zoonotic cases, indicating the bacteria were transmitted from dog to human, involving 164 strains from 17 different U.S. states.
The strains taken from dogs included a variety of serovars, or unique variants of the bacteria, many of which are relevant to human health. Although the datasets did not provide information on the severity of infections or treatment methods, the researchers confirmed that all identified strains had antimicrobial resistance genes for drug categories considered critically or highly important by the World Health Organization.
“We found 16 nontyphoidal Salmonella isolates from humans that were closely related to various dog-associated strains,” said Sophia Kenney, a doctoral student in molecular, cellular, and integrative biosciences and member of the Department of Animal Science who led the study. “Our findings underscore the need for responsible antimicrobial use and ongoing biosurveillance, considering all possible transmission routes, including companion animals, through a ‘One Health’ approach that links human, animal, and environmental health.
Kenney further emphasized that responsible antimicrobial use in veterinary medicine for companion animals is essential to combat antimicrobial resistance within the One Health framework.
“When discussing Salmonella, our thoughts often go to agriculture, like considering eggs or beef. However, unlike cows, dogs often share close quarters with us, sharing our beds and affection,” she noted. “Since we maintain a strong bond with our dogs, it’s important to explore their role in transmitting zoonotic diseases like Salmonella, as they can certainly become infected. While Salmonella infections in dogs are relatively uncommon, we are aware of foodborne outbreaks tied to dog treats or contaminated pet food.”
Co-author Nkuchia M’ikanatha, lead epidemiologist at the Pennsylvania Department of Health and associated researcher with Penn State’s Department of Food Science, recounted a past outbreak of multidrug-resistant Salmonella connected to pig ear treats for pets, which made 154 people ill across 34 states.
“This serves as a reminder that basic hygiene actions, such as washing hands, are crucial to safeguarding both ourselves and our pets – our dogs are part of our families, yet even the healthiest canine can carry Salmonella,” he stated. “Salmonella has been intertwined with human history since agriculture began, and new studies suggest it may have been present alongside domestication practices for around 10,000 years. Considering nearly 40% of households in Pennsylvania and over half in the U.S. have dogs, we must acknowledge the persistent threat of Salmonella and stay proactive in avoiding its spread within our households.”
Erika Ganda emphasized that bacteria are not entirely “good” or “bad” – their impact depends on the context. While some bacteria, like Salmonella, can pose significant health risks, others are vital for maintaining health in humans and pets. It’s essential to be aware of the risks of interacting closely with animals and to stay informed.
“Moreover, many studies highlight the substantial physical and mental health benefits of dog ownership, such as lower stress levels and increased exercise,” Ganda added. “Our aim is not to deter pet ownership but to ensure that people understand potential risks and take straightforward measures, like practicing good hygiene, to protect both their families and their beloved pets.”
This research was funded by the U.S. Department of Agriculture, the Centers for Disease Control and Prevention, the National Institutes of Health, and the U.S. Food and Drug Administration.
