In many cases, the presence of intestinal parasites is tolerated by the “host” animal. The worms thrive, robbing the infested dog nutrients. Meanwhile eggs are released through the feces to extend the cycle of infestation to other potential hosts. The animal may not have any signs of gastrointestinal inflammation and may not even appear sick. It can even come as a surprise to pet owners when they are informed that their apparently healthy pets had parasitic eggs in their stools.
Sometimes, intestinal parasites cause symptoms that are vague and seemingly unrelated to the digestive system. A parasitized animal may become anemic or less resistant to infection, and have a dry, dull coat or itchy, flaky skin. The larval stages of some internal parasites travel through the lungs to provoke intermittent moist coughing. Weight loss can be dramatic despite a healthy or augmented appetite. Other individuals simply become depressed, eating less or not at all as they withdraw from normal social interaction. By the time any of these symptoms appear, diarrhea or vomiting may well commence, but even these effects may never be seen in heavily parasitized pets.