About 1 in 15 house cats may be carrying a common intestinal parasite that can also infect humans, according to a new study examining more than 157,000 cats across North America. Researchers found that 6.3% of cats tested positive for Giardia duodenalis, a microscopic parasite that causes an intestinal illness commonly known as “beaver fever.” Nearly one in five infected cats carried strains with the potential to spread to humans. The findings, published Wednesday in the peer-reviewed journal PLOS One, also revealed that kittens younger than 1 year old were significantly more likely to test positive than older cats. Researchers...