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June 28, 2012 at 6:00 AM

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Veterinary Q&A: Poop as a diagnostic tool

SandyFecal flotation.jpgFecal testing: A fecal flotation test is set up at Phoenix Central Laboratory in Mukilteo. A flotation technique uses a solution and either passive or active flotation to separate parasite eggs from debris in the sample and allow them to be identified under a microscope by egg size and morphology.


Sandy at phoenix.jpgDr. Sandy Willis, a small animal internal-medicine consultant at Phoenix Central Laboratory in Mukilteo, answers this week's questions.

Question: Vets typically want to test a stool sample from our pets during an annual exam. It can be a smelly and messy collection, and many pet owners ignore the request. How valuable a diagnostic tool is poop?

Answer: The importance of a routine fecal examination and deworming has grown in recent years.

A fecal exam is very helpful in health and disease. It will identify most gastrointestinal parasites in a healthy pet and those that may be causing disease in a sick pet with a variety of signs, including diarrhea, vomiting, poor skin and hair coat, weight loss, etc.

Most pets acquire parasite infections from the environment because parasite eggs often can exist for long periods of time in the soil and grass. Fecal examinations in healthy pets will identify asymptomatic shedders, allowing us to treat them, eliminate shedding,
serving to reduce overall contamination and exposure of other pets to infection.

SandyRoundworms 2.jpgSome parasites, such as toxocariasis (roundworm infections, shown right) and toxoplasmosis are zoonotic, meaning that if eggs are ingested by people, they can develop disease. This occurs rarely, but routine fecal examination and deworming of our pets is important to the health of our families.

Furthermore, restricting access of children to contaminated areas, such as sandboxes, pet-walk areas and other high-traffic areas, is important.

An important zoonotic parasite is the raccoon roundworm Baylisascaris. Raccoons defecate in areas called latrines, and surrounded soil can be contaminated with Baylisascaris eggs.

People should discourage raccoons from their yards but not feeding raccoons or other animals around their homes, carefully removing any raccoon fecal material, and not allowing children to play in areas where raccoons have been.

Question: What can a fecal sample tell you about a dog's health?

Answer: Fecal examination will identify internal parasites, such as worms, coccidia including giardia, and sometimes larvae such as lung worms.

In puppies, parasite infections often come from the mother, so the health of the puppy and bitch can be assessed by a fecal examination.

But the exams do not identify all infections, and, thus, routine deworming is important even if fecal tests are negative.

This is particularly important in the puppy and in recently infected older dogs. In these dogs, worms are present in the intestines but they are not yet shedding eggs, resulting in a negative fecal examination.

Our common antiparasiticals have become so much more advanced in recent years.

They are safer, easier to administer and kill and prevent more infections. However, the fecal examination remains important to make sure we are treating the dog or cat with the most appropriate antiparasitical.

Clients should seek advice from their veterinarian on which dewormers are best. There are many out there, some less effective than others, and the veterinarian's advice can save costs by making sure the right one is selected from the beginning. We also have to be careful with cats and make sure they receive dewormers appropriate for the feline.

Question: What can't a fecal sample tell you?

Answer: There are other causes of diarrhea, including pancreatic insufficiency, small intestinal disease, hormonal problems, even cancer. Routine fecal examination will not diagnose these.

Bacterial causes of diarrhea are rare in small animals. A fecal culture, looking for unusual bacteria in the stool, is needed to diagnose a bacterial diarrhea. Parvovirus diarrhea is not diagnosed on a routine fecal examination, but there is another fecal test for this viral diarrhea.

Question: What specifically are you looking for in fecal tests?

Answer: We are looking for worms, small, moving organisms such as tritrichomonas and eggs of common gastrointestinal parasites.

Question: Is one stool sample usually enough?

Answer: Generally, yes. Sometimes we prefer to check multiple fecal samples because shedding may be intermittent, which can be the case with a giardia infection. In a patient with diarrhea, we may end up treating for gastrointestinal parasites even though a fecal sample is negative because a negative result does not absolutely rule out all parasites.

SandyCoccidia.jpgQuestion: What kinds of common issues are typically found?

Answer: The worm eggs: roundworms, hookworms, whipworms, coccidian, shown right, including giardia in small animals. Stomach worms, tapeworms, some whipworms and hookworms are seen in large animals.

These must be distinguished from common contaminants in stool, including environmental yeasts and fungi, pollen and other plant material, grain mites and parasites of other species (such as rodents, amphibians, large animals and horses) that are acquired from eating the species (i.e. frogs) or their stool (sheep and cattle).

Parasites from other species are just passing through, cause no disease in the dog and cat and do not require treatment.

Question: What are some of the more unusual diseases detected?

Answer: We can occasionally find organisms that are not related to the gastrointestinal tract, such as skin parasites like demodex and sarcoptes. These are mites that are usually picked up in skin scrapings made of the skin, placed on a slide and examined under a microscope. Sometimes the itching dog or cat will ingest these mites, they will pass unchanged through the gastrointestinal tract, and we will find them in the stool. Pretty cool.

We have occasionally seen a huge load of worm eggs from a species other than the one being sampled, such as deer worm eggs seen in the feces of a dog that routinely ingests deer poop!

We occasionally also see eggs that might cause significant disease in a sheep, goat or llama -- in the stool of a dog. It is not necessary to treat the dog for the parasite,
because these worms are generally species specific and only cause a problem in the natural host, but it is important to contact the owner of the pasture and have them do a routine deworming of their livestock.

Question: What is the worst thing it can reveal?

Answer: Sometimes we see such large infestations of parasites that the patient must be really ill. Overwhelming gastrointestinal parasitism can cause severe illness and death, particularly in young and immunocompromised patients.

sandySalmon poisoning.jpgIn the Pacific Northwest, we also see a disease called salmon poisoning, shown right. Salmon poisoning occurs in domestic and wild dogs from northern California and Washington. This disease can be fatal if not identified and treated.

It is caused by a small microscopic organism called a rickettsia. Clinical signs include fever, not eating, weight loss, vomiting and diarrhea, which can sometimes be bloody. Signs are severe and dogs can become very ill, needing immediate veterinary care.

The interesting aspect of salmon poisoning is this: the rickettsia, called Rickettsia helminthoeca, is carried within a trematode or fluke. The fluke requires two other life-forms, the snail Oxytrema spp., which is only found in fresh and brackish stream waters in our coastal areas, and salmonid fish (salmon), certain nonsalmonid fish (such as trout) and the Pacific giant salamander. The dog becomes infected by eating or sometimes even licking, a fish or salamander. We diagnose the infection by finding the fluke eggs in a stool sample. It is rare to find the rickettsia agents themselves.

Salmon poisoning only occurs from the ingestion of raw fish. Cooked fish do not present a problem. Thus owners should really discourage their dogs from eating any raw fish.

This disease is not seen in cats.

Question: Which diseases, parasites, etc., can only be detected in an analysis of poop?

Answer: We can only detect the presence of gastrointestinal parasites, such as worms, trichomonads, coccidia, etc., by a fecal examination. There are no blood tests for these organisms.

Question: Are there any situations in which diseases/problems can be caught early by examining poop, before more serious symptoms develop?

Answer: We can occasionally detect fecal parasites before we see signs of disease such as diarrhea, blood in the stool, weight loss, poor skin and hair coat and condition, etc.

In addition -- and more importantly -- some parasites are zoonotic, meaning they can cause an aberrant infection in man, such as roundworms and certain hookworms. Thus we do want to make sure our pets are parasite free by performing routine fecal examinations and deworming.

In salmon poisoning, if we find the fluke eggs on a routine fecal examination, we will generally treat to prevent the disease with a tetracycline antibiotic.

Question: Vets usually want the samples to be "fresh." Why?

Answer: Even the finding of one egg can be diagnostic, thus we want the samples to be fresh. With time, samples and eggs dry out and disintegrate.

Also, fecal samples in the environment can quickly become contaminated with fly eggs, free living larva or worms from the soil, and other contaminants that can be confused with real parasites.

Question: What is the best way to collect a sample? What do you suggest it be scooped up with?

Answer: The sample can be scooped up with anything clean and submitted in a special fecal vial provided by the veterinarian, a clean dry cup of any type with a lid, or even a plastic bag. The key is to not gather up too much of the environmental contamination, such as leaves and dirt and little box clay.

We usually only need one to six grams of a sample, thus the owner does not need to provide a huge amount. When there is diarrhea, the sample size should be larger. With firm stool, we need less.

Question: What is the best sanitary way to keep a sample if you can't get to the vet immediately?

Answer: Keep the sample in a container with a lid, or in a bag that is closed. I would keep it in a cool place.

As pets defecate at least one to two times a day, samples should be collected on the day they are submitted or the day before so they shouldn't need to be kept for long periods of time.

Question: How is a fecal sample prepared for review?

Answer: Fecal samples are analyzed either at veterinary diagnostic laboratories or within the practice. The basic technique of the fecal procedure is to first identify any large parasites within the sample.

We may take a small sample, mix it slightly with water and do a direct examination under the microscope for any moving parasites. Then, another small sample is prepared for a fecal flotation. A flotation technique uses a solution (can be sugar solution, zinc sulfate, sodium nitrate, etc) and either passive ( the sample sits on the counter for a given length of time) or active (centrifugation of the sample) flotation to separate parasite eggs from debris in the sample and allow them to be identified under a microscope by egg size and morphology.

Question: How much does an analysis usually cost?

Answer: This varies depending on the technique and whether the fecal sample in done in the veterinary clinic or sent out to a veterinary diagnostic laboratory. Costs can vary from roughly $25 to $45. Clients are urged not to shop tests based on cost alone because the cheapest fecal test may not be run the complete way with centrifugation. Also, a clinic is not going to simply run a fecal test without a physical examination, an interpretation of the results and appropriate therapy.

Dr. Sandy Willis


Dr. Willis is a small animal internal-medicine consultant for Phoenix Central Laboratory, an independent veterinary diagnostic laboratory in Mukilteo. She consults with veterinary professionals on internal medicine and diagnostic testing, organizes continuing education provided by the laboratory to the veterinary community, including seminars and wet labs, and contributes to their newsletter and website. She is past president of the Seattle King County Veterinary Medical Association as well as the Washington State Veterinary Medicine. Willis serves as staff for Giselle, a tabby Oriental Shorthair, and Tiger (you guessed it, the tiger cat).

All photos courtesy of Dr. Sandy Willis

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Do you have a question about pet health? Ask now! We'll pose some of your questions to a local vet in an upcoming post.

Read earlier Q&A columns here.



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