Routine Fecal Testing: FAQs for Dog Owners

By Catherine Barnette, DVM

What is the purpose of routine fecal parasite testing?

Routine fecal examinations are used to detect intestinal parasites in your dog. These parasites may include worms (such as hookworms, roundworms, and whipworms) and microscopic parasites (such as Giardia or Coccidia). Parasites not only cause intestinal disease in dogs, some of them can also be infectious to humans (hookworms, roundworms, and Giardia).

How does my veterinary hospital perform fecal parasite testing?

Fecal testing must be performed on fresh feces. Your veterinarian may have you bring a fresh sample from home, or they may collect a small sample directly from your dog’s rectum.

"Fecal testing must be performed on fresh feces."

A fresh fecal sample is mixed with a special solution in a vial and either centrifuged (spun at high speeds) or allowed to sit undisturbed for a predetermined period of time. The purpose of centrifugation or undisturbed fecal flotation is to isolate parasite eggs at the top of the vial. The material that rises to the top of the vial is then examined under the microscope, to look for the presence of worm eggs and other microscopic parasites.

In some cases, your veterinarian may also perform a fecal smear. This involves placing a small amount of your dog’s feces on a microscope slide and examining it directly under the microscope, without any special processing. Fecal smears are primarily used to diagnose Giardia, although they can also be used to obtain other information about your dog’s intestinal health.

How often should my dog’s feces be tested for parasites?

During their first year of life, puppies should have several fecal parasite exams. Intestinal worms are very common in puppies and can cause more problems in younger dogs, so early detection is important. Not all intestinal parasites are addressed by common dewormers, so fecal parasite exams are important even in puppies that are receiving regular deworming.

In adult dogs, fecal parasite testing should be performed every six months. This is true even if your dog is on heartworm prevention or other parasite prevention.

If I am not seeing worms in my dog’s stool, how can he still have worms?

Most intestinal worms remain within the body and are not shed in the stool. Instead, these worms lay microscopic eggs that are shed into the environment. A fecal parasite examination searches for these eggs.

Can my dog have intestinal worms even though he is on heartworm prevention?

While most monthly heartworm preventatives are very effective at preventing intestinal worms, breakthrough infections can occur. Additionally, not all heartworm preventives are designed to prevent all intestinal worm preventions. For example, ivermectin-based heartworm preventatives do not prevent whipworms, and long-acting heartworm prevention injections have only short-lived efficacy against intestinal worms. Therefore, even pets that are receiving consistent heartworm prevention may still develop intestinal worms.

How serious are intestinal parasites?

The effects of intestinal parasites can vary significantly, depending on the parasite and the overall health of the dog. Effects of common parasites include :

  • Roundworms. Roundworm infections in adult dogs are often asymptomatic. In young dogs or severely infected adults, however, signs may include vomiting, diarrhea, weight loss, a dull coat, and a potbellied appearance. Roundworm larvae also migrate through the lungs as a part of their life cycle, so coughing may be observed.
  • Hookworms. Hookworms embed in the wall of the intestine, sucking blood from their host. Therefore, the most significant effect of hookworms is anemia, resulting in lethargy, weakness, and pale gums. Weight loss and bloody diarrhea are also commonly observed.
  • Whipworms. Whipworms often cause bloody diarrhea in dogs. Additionally, affected dogs may be weak and may become increasingly debilitated over time.
  • Giardia. This protozoal parasite often causes severe watery diarrhea, which may or may not be accompanied by vomiting and weight loss.
  • Coccidia. Although infection with this protozoal parasite is often asymptomatic in healthy adults, it may cause diarrhea and other signs of illness in puppies or debilitated adults.

How will my veterinarian treat intestinal parasites that are found on routine fecal testing?

If your veterinarian finds evidence of intestinal parasites on routine fecal testing, they will recommend appropriate treatment to eliminate the parasites. Depending on the parasite, your dog’s treatment may include as little as one to two doses of dewormer or a prolonged course of oral medication. Each intestinal parasite has its own unique treatment requirements.

Your veterinarian may also recommend a change in your dog’s heartworm preventive. If your dog is encountering a particular parasite in the environment that is not prevented by their current heartworm preventative, a change in prevention can prevent reinfection with the parasite.

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