Fleas and ticks are the most common external parasites that affect dogs. Fleas can cause itching, allergic reactions, and anemia in severe cases. They reproduce rapidly and can infest your home in no time. Ticks, on the other hand, can transmit serious diseases such as Lyme disease, Rocky Mountain spotted fever, and ehrlichiosis. Mosquitoes, while less invasive, can transmit heartworm disease, a potentially fatal condition if left untreated. Understanding these risks is crucial for dog owners, as preventing these infestations is much easier than treating them.