Yes, dogs can pass roundworms to cats, as well as other animals and even humans. Roundworms are transmitted through the ingestion of infected eggs or larvae, which can be found in contaminated soil, water, or feces. When a dog ingests infected material, the roundworm larvae can migrate to the dog's intestines and grow into adult worms, which produce eggs that are then shed in the dog's feces. If a cat then ingests the infected feces or contaminated material, it can become infected with roundworms as well. Always practice good hygiene and regularly deworm all of your pets to help prevent the spread of roundworms and other parasites. You should also dispose of your pet's feces promptly and wash your hands thoroughly after handling pets or their waste.