Fleas can be irritating for people. They’re not just a minor nuisance, though. The pests can be extremely distressing for your pets. As they hitch a ride on an animal, fleas bite and suck blood, which can cause inflammation and itching. Fleas can also carry disease. They can infect cats with Bartonella, the bacteria responsible for cat-scratch disease. These bacteria can be transmitted to humans. Fleas can also serve as a host for tapeworms and pass the parasites to your pets or, more seldom, you.