Internal parasites are organisms that live inside the bodies of their hosts, often causing harm. Common types include worms, protozoa, and flukes. These parasites can inhabit various organs, such as the intestines, liver, or bloodstream, and they often feed on the host's nutrients, leading to health issues. Infections from internal parasites can affect many animals, including pets like dogs and cats, as well as humans. Symptoms may include weight loss, diarrhea, and fatigue. Proper hygiene, regular veterinary check-ups, and preventive medications can help reduce the risk of internal parasite infections.