Dog owners and their pets may exchange harmful mouth bacteria that can cause gum disease and tooth decay in both humans and canines, according to a report in Archives of Oral Biology. Previous research has shown people can transmit oral bacteria to children through close daily contact. But few studies have looked at the bacteria exchanged between people and their pets.

About 5% of canines get dental caries, which includes tooth decay and cavities. But rates of periodontitis, an inflammatory mouth disease, in dogs have been reported to range from 50% to 70%.

Researchers late last year worked with dog owners in Japan to assess the prevalence of 10 bacteria that are associated with periodontitis in people. They also analyzed an oral microbe commonly found in dogs but not humans. Study participants were 81 members of 64 families that owned 66 dogs of various breeds and ages. Participants were divided into three groups: Most of the people had a high degree of contact with dogs while the others had little or no contact with dogs.

Analysis of dental plaque found all 10 of the human bacteria in dogs and humans. The most common—Tannerella forsythia, Porphyromonas gulae, and Campylobacter rectus—were detected in significantly higher levels in dogs than owners. As many as a quarter of the dogs and owners with close contact shared Eikenella corrodens bacteria. Periodontal bacteria were more prevalent in high-contact relationships and in older dogs.

P. gulae, rarely detected in humans, was found in 13 owners and their dogs, including two with low-contact relationships. This finding suggests bacteria can be transmitted from dogs to humans even with low contact, researchers said.

Caveat: Data about pre-existing periodontitis in dogs and owners wasn’t available.

Title: Distribution of periodontopathic bacterial species in dogs and their owners