Most of the bacteria in your dog’s mouth are harmless, but there are exceptions. "Dogs can carry a number of zoonotic pathogens, or organisms spread from animals to humans that cause disease," Reynolds tells BuzzFeed Health. You can get these from dog kisses or from contact with infected feces. These include bacteria and parasites, like Salmonella, Pasteurella, Campylobacter, Cryptosporidium, Leptospira, Giardia, ringworm, and hookworm. Yuck.
"Some of these are common causes of diarrheal illness outbreaks in the US," Reynolds says. Just this year, an outbreak of Campylobacter infections in sick puppies spread to 67 people, and 17 were hospitalized.
These pathogens are common, Reynolds says, and your dog can pick them up anywhere — from sniffing other dogs (and their poop), contaminated food or water, streams or ponds — but you can’t always tell when they do. "These can make your dog sick (usually with diarrhea), but oftentimes the dog will carry them asymptomatically," Reynolds says. So you may not even realize that your pup caused your stomach bug. The only way to find out what your dog is carrying is by sending a stool sample to your veterinarian for testing.