The Benefits and Limitations of Fecal Float

CAPC recommends testing all dogs for roundworms, hookworms, and whipworms by fecal flotation with centrifugation. Centrifugal fecal flotation is the best way to do a float, but some limitations of fecal floats alone can lead to false negatives:

• During the prepatent period, the fecal float will be negative but there can still be clinical signs of an infection. Prepatent periods can vary by parasite, ranging from as short as two to three weeks for hookworms to as long as three months for whipworms.
• Intermittent shedding is also a concern, as parasites do not shed eggs continuously, and a single fecal sample may not capture eggs from all the parasites present. For flea tapeworms (Dipylidium caninum), fecal floats rarely detect infection because the segments rarely release eggs into the feces and are shed intact on the surface of the stool.
• In single-sex infections only male or female parasites are present, so no eggs are shed. This renders the fecal float negative despite infection that can lead to clinical signs.
• Pollen and other debris in the feces can be misidentified as parasite eggs, leading to a misdiagnosis.
• The inappropriate identification of eggs from other species as a result of coprophagy (the ingestion of infected feces) may also occur.

  Don't rely on eggs for a diagnosis. Get a free upgrade to IDEXX Fecal Dx® antigen testing

Supplementing Fecal Float Results With Fecal Antigen Testing

Due to fecal floats' insensitivity, fecal antigen detection can be used for common parasites including Giardia—the antigens are shed by adult worms even in the absence of eggs. Also, fecal antigen is also a more accurate and sensitive method of detecting flea tapeworm infections. Fecal antigen tests can identify roundworm, hookworm, and whipworm infections in the prepatent stages as well as with intermittent egg shedding. Early detection during the prepatent period will also reduce the frequency of environmental contamination with potentially infectious eggs and can help remind clients that dogs are continually re-exposed. This can serve as a stimulus to start a regular preventive or repeat deworming targeted at the specific species.

Parasite Prevalence and Detection

Fecal parasites can be more common than veterinarians realize. In dogs and cats, the prevalence of infection with each intestinal parasite varies by region and tends to occur more frequently in shelter pets—or pets adopted from shelters who haven't been thoroughly dewormed. Indeed, regular deworming is an important component of preventive medicine. A 2005 study of shelter dogs in northern California showed that about one-third of dogs with diarrhea had evidence of gastrointestinal parasites on a fecal float, with Toxocara canis the most common parasite—found in nearly 15% of these symptomatic dogs.

Recently, more than 750,000 IDEXX Reference Laboratories dog and cat fecal results were analyzed to determine the overall prevalence of various nematodes using fecal float (by centrifugation) compared to fecal antigen enzyme-linked immunosorbent assay (ELISA) testing. The results showed improved sensitivity across roundworms, hookworms, and whipworms:

• Roundworm eggs were detected in 2.2% of the specimens. The roundworm-specific antigen ELISA was positive in an additional 1.3% of specimens that were negative for roundworm eggs, bringing total roundworm prevalence to 3.5%.
• Hookworm eggs were detected in 1.7% of the specimens. The hookworm-specific antigen ELISA was positive in an additional 2.0% of specimens that were negative for hookworm eggs, bringing total hookworm prevalence to 3.7%.
• Whipworm eggs were detected in 0.7% of the canine specimens. The whipworm-specific antigen ELISA was positive in an additional 1.0% of specimens that were negative for whipworm eggs by fecal O&P testing, bringing total whipworm prevalence to 1.7%.

Tapeworm Detection

According to CAPC, the reported prevalence of Dipylidium caninum in published studies varies from less than 5% to 50%-60% in dogs and cats, with differences largely based on the testing strategy. Fecal floats are notoriously insensitive for the detection of tapeworm eggs because of the reproductive biology of the worm, resulting in a large underestimation of the prevalence of infection in studies based on fecal floats alone. In contrast, estimates based on direct examination of the small intestine (generally at post-mortem) have been most accurate for detection, and usually result in much higher prevalence than surveys reporting only fecal flotation results—as high as 60% in dogs and over 20% in cats. As with giardia, and increasingly with nematode species, antigen testing can improve the detection of tapeworms compared to fecal float alone. In a study using about 900 fecal submissions to IDEXX Reference Laboratories, D. caninum antigen was detected in 5.8% of the specimens, while only two (0.22%) were positive on fecal flotation.

CAPC recommends testing for fecal parasites at least four times in the first year of life for puppies and kittens and at least two times per year in adults depending on patient health and lifestyle factors. While fecal float using centrifugation is the mainstay diagnostic test, limitations of this assay suggest that fecal antigen testing should be combined with microscopic examination of feces for eggs to increase intestinal parasite detection. Earlier and more sensitive detection techniques can help decrease the morbidity associated with intestinal parasites in dogs and cats, and will even help prevent infections in people since many of these parasites are zoonotic.