Not all dogs with hookworms exhibit noticeable symptoms, especially otherwise healthy adult dogs. Symptoms are most common in young puppies or dogs infected with a high number of hookworms. Young puppies with hookworms are more prone to life-threatening anemia. These puppies are typically weak and dehydrated. Hookworm infection in dogs can cause pale gums, weight loss, decreased appetite, and dark tarry diarrhea. Dogs may also develop skin inflammation and coughing.