Blood and mucous in diarrhea can indicate that a dog has parasites or parvo, warns Canine Journal. They are serious symptoms and should be treated with professional medical care. If the bloody diarrhea is caused by a change in diet, the symptoms pass quickly, but parvo can be deadly.
Puppies are more difficult to diagnose with diarrhea because they have softer stool than adult dogs, according to Canine Journal. Because of this, it is important to regularly check their feces and become familiar with its color and consistency; as a general rule of thumb, a dog's poop should never be liquid. Uncharacteristic accidents or an increased desire to go out can indicate that a dog has uncontrollable diarrhea.
The most common cause of diarrhea in dogs is diet, states Canine Journal. A change in diet can lead to diarrhea, as can eating an object not meant for consumption. Stress and parasites are other common triggers. Liquid diarrhea may put a dog at risk for dehydration and is a symptom of a viral or intestinal infection. Mucous indicates the presence of parasites, but it also puts a dog at increased risk of parvo.
As a general rule of thumb, bloody stool is always a bad sign, according to Canine Journal. Solid feces with fresh blood can point to internal bleeding or an ulcer, while bloody diarrhea indicates parvo or parasites, or simply puts the dog at risk of dehydration on top of other illnesses.