Fleas and ticks are the most common external parasites that may infect your pet. They can bite your pet and cause itching and discomfort. Topical medications are needed to rid your pet of fleas. You can prevent fleas, or, if your pet is unfortunate enough to have them, you can apply a medication that will kill the existing fleas and ensure they no longer lay eggs in your pet's fur. Prescriptions are the best way to rid your pet of these external parasites.