Elevating Patient Care with New Faecal Antigen Testing for Cystoisospora
For decades, one of the core screening tests for canines and felines has been the ova and parasite (O&P) test. While historically veterinarians have used this to identify common fecal parasites like Cystoisospora, guide treatment, create prevention strategies, and protect human family members from zoonotic disease, this test has a high rate of false negatives for various reasons, including human error.
More recently, science and technological advancements led to the creation of faecal antigen testing, a welcome addition to our small animal diagnostic repertoire for common parasites, including hookworms, roundworms, whipworms, and flea tapeworm. And soon, due to diagnostic advancements expected this year, we will be able to more accurately test for the common parasite, Cystoisospora in dogs and cats with faecal antigen testing.
What Is Faecal Antigen Testing?
Faecal antigen testing is a newer, more accurate means to detect parasite proteins. This is a critical distinction from traditional faecal O&P, which requires team members to collect a sample of feces and mix it with a denser floatation solution which allows the eggs shed in the host faeces to rise to the surface and be identified under a microscope. However, many infected dogs and cats can be asymptomatic, shed intermittently, have same-sex infections limiting egg shedding, have dense eggs that don't float, or have nonspecific clinical signs without a positive faecal O&P. Instead, the faecal antigen test looks for a protein secreted or excreted by the parasite into the host intestinal lumen. These unique proteins are then found by specific antibodies during testing, improving detection rates and accuracy. Faecal antigen testing currently tests for hookworm, roundworm, whipworm, and flea tapeworm.
The Importance of Adding Faecal Antigen Testing to Your Workflow
The Companion Animal Parasite Council (CAPC) recommends testing for faecal parasites at least four times in the first year of life for puppies and kittens and at least twice yearly in adults, depending on patient health and lifestyle factors. Faecal parasites, including Cystoisospora in dogs and cats, are more common in puppies and kittens. Suppose your practice relies solely on ova and parasite testing through faecal O&P. In that case, it's essential to be aware of the limitations of this testing and the many missed opportunities for early detection of parasitism, many of which could be zoonotic.
Faecal Antigen Testing for Cystoisospora
One opportunity ahead is the ability to use faecal antigen testing for Cystoisospora. Cystoisospora, formerly known as Isospora (sp) and commonly known as coccidia, is a protozoan parasite reproducing in the host's small intestine, producing unsporulated oocysts in the host's faeces. Dogs and cats can acquire this parasite by ingesting the immature form (oocyst) from a contaminated environment like soil or faeces.
We mostly think of puppies and kittens as presenting with this disease because they are commonly exposed to a contaminated environment with an immature immune system. But adult dogs and cats that experience the stress of a new move or the addition of a new family member, are immune suppressed, or deal with other chronic diseases can also be susceptible. These patients present with vague gastrointestinal signs such as diarrhoea that's classically watery, bloody, and/or with mucous, weight loss, dehydration, and lethargy. Severe cases in puppies and kittens can also cause anorexia, vomiting, and even death.
Based on the presentation and clinical signs, veterinarians usually start their database with a faecal O&P, but soon we will be able to detect this disease more accurately through faecal antigen testing. Up until now, diagnosis of Cystoisospora in dogs and cats has been made by looking for large numbers of species-specific unsporulated oocysts.
Some dogs and cats with Cystoisospora can be asymptomatic, however, these infected pets can still shed in their faeces and potentially infect other puppies, kittens, adult dogs, or cats, especially knowing that the oocysts can remain infective in the environment for several months. This is why testing is critical not just for illness visits, but also for wellness exams. Dogs and cats of all ages should have faecal testing included in wellness screenings.
Pseudoparasites
While Cystoisospora is not considered a zoonotic parasite, it is still a source of significant disease and communal transmission, making early and accurate detection significant. One of the factors that confound accurate diagnosis of parasitism, especially Cystoispora, is the presence and misdiagnosis of pseudoparasites. These are oocysts that dogs and cats eat, yet they pass through without being pathogenic. Eimeria spp. is a common "parasite" in the faecal O&P of healthy adult dogs, yet dogs don't host these parasites. With faecal O&P tests, these pseudoparasites can raise alarm, but with faecal antigen testing, it's simpler to rule out false positives. Antigen testing does not cross-react with other species of coccidia and therefore allows differentiation from Eimeria, a pseudoparasite often found in the faeces of dogs. This avoids unnecessary treatment of the patient through misidentification.
While centrifugation using faecal O&P may still be the go-to test for some veterinarians, limitations suggest that faecal antigen testing should be combined with microscopic examination of faeces for eggs to detect up to five times more intestinal parasite infections than just faecal O&P alone.
A key facet of veterinary medicine has always been preventive care—and continuing to educate clients on exams and diagnostic screening tests will help raise awareness of their importance. Adding faecal antigen testing for patients can help identify a large number of parasite infections earlier and with greater accuracy to best protect patients and their families.
