All four of these diseases can be prevented by annual vaccinations. If a dog is not vaccinated, early diagnosis of the symptoms of each disease is imperative. External Parasites Symptoms . Fleas, ticks, lice, maggots, and mites are common external parasites that prey on animals. All cause animals to scratch excessively, which can lead to hair loss.
Fleas are tiny brown insects that move through the animal's coat.
Ticks are small, round, dark-colored insects with hard shells that attach themselves to an animal's skin. Lice are small, dark-gray insects that remain in one place on an animal's body. Maggots look like small worms. Mites, which are invisible to the unaided eye, characteristically cause skin and ear irritation. External parasites can be readily eliminated and controlled with commercially available powders, baths, sprays, and dips.