Laurel E. Redding, PhD

While both humans and pets are at a risk of developing a clostridiodes difficile infections (CDI), new research shows intra-species transmission of the disease is relatively rare, with only 2 of 39 households tested showing positive tests in both an owner and a pet.¹

A team, led by Laurel E. Redding, PhD, Department of Clinical Studies-New Bolton Center, University of Pennsylvania, School of Veterinary Medicine, assessed how often pets belonging to patients with CDI carry genetically related C difficile isolates.

“Companion animals have been shown to carry Clostridioides difficile strains that are similar or identical to strains found in people, and a small number of studies have shown that pets carry genetically identical C. difficile isolates as their owners, suggesting inter-species transmission,” the authors wrote.

However, it is currently unknown what the directionality of transmission ultimately is and what the frequency of which animals acquire C difficile following the infection of their owner is unclear.

The Cohorts

In the study, the investigators enrolled pet owners from the University of Pennsylvania Health System (UPHS) and The Ohio State University Wexner Medical Center (OSUWMC) who had diarrhea with or without positive C. difficile assays.

The investigators tested the feces of the pets and owners for C. difficile using both anaerobic culture and PCR assays.

The majority of patients (97%; n = 29) reported their dogs lived indoor/outdoor, with close contact between themselves and the dog being tested lick owners face and hands frequently.

The fecal samples first underwent selective enrichment by mixing with cooked meat broth and incubating anaerobically for 48 hours, with cultures for toxigenic isolates confirmed with qPCR using an in-house multiplex PCR that detects the tcdA and tcdB genes.

The investigators also investigated animal-level health and environmental factors as risk factors for pets fecal shedding of C difficile in the OSUWMC and used Fisher’s exact text or the Wilcoxon rank-sum test to identify the difference in distribution of each factor among colonized and non-colonized animals.

Little Transmission

When microorganisms were obtained from both the owner and pet owner with the same toxin profile or ribotype, the investigators performed genomic sequencing on the isolates.

Overall, the study included fecal samples from 59 humans, 72 dogs, and 9 cats from 47 total households.

The results show C. difficile was identified in 30 humans, 10 dogs, and 0 cats, with 2 households having C difficile detected in both the owner and at least 1 pet.

Of these households, 1 had C. difficile isolates of different toxin profiles/ribotypes (A+/B+ / RT 499 from the owner, A-/B- / RT PR22386 from the dog).

The other household featured genetically identical isolates with 1 SNP differences.

The results also show the dog from the household with identical isolates received a recent course of cefpodoxime and metronidazole antibiotics.

“Our findings suggest that inter-species transmission of C. difficile occurs infrequently in households with human C. difficile infections,” the authors wrote.