A parasite is an organism that lives on or in another organism and gets its food and shelter at the expense of its host. More common than we think, parasites invade humans and animals and manifest in disease, some of which may cause substantial damage to the intestinal tract. One class of parasites that can cause disease is protozoa, one-celled organisms that often cause their host little to no harm. However, some single cell organisms are highly injurious to canines, causing severe diarrhea, excessive weight loss, general sickliness and even death. Due to acute or chronic diarrhea, a canine may become dehydrated. Malnutrition is also a particularly serious outcome of intestinal protozoa, and is particularly dangerous for puppies and adolescent dogs who have underdeveloped immune systems, or dogs that are immunocompromised. 

Two common intestinal parasites found in canines are Coccidia, microscopic protozoans that live in the intestinal wall. and Giardia, the most common intestinal parasite worldwide. Giardiasis, an infection of the small intestine caused by the presence of Giardia, occurs when dogs ingest infected offspring that are shed in another animal's feces.  Though most dogs with giardiasis will not present with symptoms such as chronic diarrhea or vomiting, the presence of the parasite may still lead to a malabsorption of nutrients, damage to the intestinal lining and problematic digestion. A dog with giardiasis may not demonstrate a change in appetite, but will still experience weight loss. If symptoms do materialize, the dog will likely have acute or intermittent diarrhea. Another intestinal parasite found in canines is Coccidia, tiny parasites that can cause an infectious disease called coccidiosis. As with giardiasis, dogs may carry the parasite, but be asymptomatic. Puppies or immunocompromised dogs may have particularly watery diarrhea mixed with mucus or blood. If left untreated, severe cases of coccidiosis may be fatal. 

Unsanitary or overcrowded kennels, pet shops and breeding facilities are commonly contaminated with intestinal parasites. Parks and lawns also provide dogs with opportunities to ingest other dogs’ feces, the most common way that dogs spread infection.

A parasite is an opportunist organism that feeds off its host. Protozoan parasites may invade a dog’s intestinal tract and cause infections such as Coccidia and Giardia.

Coccidia are intestinal protozoans that live in the intestinal wall.  Coccidia are often spread when the canine eats the infected feces of another animal.  While most dogs with coccidiosis are often asymptomatic, puppies and immunocompromised dogs may develop severe bloody, mucoid diarrhea. In such cases, a lack of veterinary treatment may cause death.

Giardia, the most common intestinal parasite worldwide, are intestinal protozoans that live in the small intestine of dogs. Infection with Giardia is common, but disease is rare. Like Coccidia, young and immunocompromised animals may develop gastrointestinal illness featuring severe diarrhea, dehydration and weight loss.  Older, healthy dogs are usually asymptomatic.

The presence of protozoan parasites is not always easy to detect. The veterinarian will perform a routine examination, paying attention to the dog’s appearance, reported symptoms and medical history.  The primary diagnostic tool is a stool sample, though, due to the small size of the protozoa and its intermittent appearance, a fecal examination must be repeated every few days. The stool is examined microscopically for presence of protozoal parasites.

Even if the stool sample doesn’t reveal the presence of parasites, a veterinarian will often treat the dog empirically. An antiparasitic drug may be prescribed to kill Giardia and Coccidia in the intestine. A sulfa-based antibiotic may be given, as well as treatment for dehydration.

Both of these infections have the potential to cause severe diarrhea which can lead to serious consequences, if not treated with therapy for the dehydration that can result. Your veterinarian may feel it necessary to hospitalize your pet and provide intravenous fluids and antidiarrheal medication until she feels that he is stabilized enough to return home.

The dog’s living environment must be safely treated to avoid re-infection.  Other dogs in frequent, close contact should also receive treatment. For healthy dogs with symptoms, a full recovery should occur through the administration of proper medications and the maintenance of a sanitary environment.