Q: Can cats that stay indoors get parasites? My veterinarian recommends that I apply a parasite preventive to my cat Seymour’s skin every month, but I don’t understand why it’s necessary. A: While cats that spend time outside are more likely to encounter parasites, even indoor-only cats can become infected. Three types are common. The first is fleas. These pests catch a ride into our homes on our shoes and pant legs and sometimes on indoor-outdoor pets. Not only do they bite, drink blood, and cause itchiness, but they also transmit tapeworms to cats and cause a variety of human illnesses, from cat scratch disease to the plague. The second is intestinal parasites, such as roundworms and hookworms. Indoor cats “catch” these worms when they capture and eat a creature, such as a cockroach or mouse, that carries the immature parasites. Moreover, roundworms, which are widespread in the environment, produce …