Antigen detection, cultures, and PCR and enterotoxin tests
Fecal antigen tests may be a useful addition to routine flotation methods.3 ELISA kits are available for Giardia species antigen detection (e.g. SNAP Giardia Test—Idexx Laboratories; ProSpecT Giardia—Remel).
Fecal bacterial and trichomonad cultures for Campylobacter jejuni and Tritrichomonas foetus, respectively, are usually low-yield but are appropriate in cases in which signalment and clinical signs suggest the possibility
Infection with C. jejuni is most often diagnosed in cats less than 6 months of age and is associated with mucoid diarrhea with fresh blood. Bacterial
culture of fresh feces remains the most reliable way to establish a diagnosis. The organism is microaerophilic, so use anaerobic
swabs for transport. Inform the laboratory ahead of time if Campylobacter species infection is suspected since special culturing methods are required. Campylobacter jejuni has been identified in both asymptomatic cats and in cats with diarrhea, so interpret positive culture results with caution.4
Tritrichomonas foetus usually affects young cats and kittens kept in crowded environments.5 Clinical signs consist of waxing and waning chronic large bowel diarrhea with blood, mucus, flatulence, profound anal irritation,
and involuntary passing of feces. Tritrichomonas foetus can be cultured by using a commercially available culture system (InPouch TF-Feline—BioMed Diagnostics). A small fecal sample
is needed to inoculate the medium inside the pouch, which is then held at room temperature for up to one week. It should be
examined under the microscope every day for evidence of the motile trophozoites.
The most sensitive method for confirming tritrichomoniasis is a fecal polymerase chain reaction (PCR) test. This test is performed
at Texas A&M University, College of Veterinary Medicine Gastrointestinal Laboratory and at North Carolina State University,
College of Veterinary Medicine Intestinal Pathogens Research Laboratory. Information regarding sample handling and submission
is provided at http://www.cvm.tamu.edu/gilab/assays/Tritrichomonas.shtml and http://www.cvm.ncsu.edu/docs/personnel/gookin_jody.html.
Clostridium perfringens enterotoxicosis (CPE) is a less common cause of diarrhea in cats. Keep in mind that C. perfringens may be isolated from the feces of clinically normal cats.6 A trigger, such as antibiotic administration, diet change, or intestinal pathogen coinfection, causes the vegetative form
of the organism to sporulate and release enterotoxins. CPE cannot be presumptively diagnosed based on findings of fecal cytologic
examination alone (Figure 4) because large numbers of endospores have been reported in the feces of healthy cats.7 Immunodetection of fecal enterotoxin is available as a reverse passive latex agglutination assay (PET-RPLA Toxin Detection
Kit—Oxoid) or ELISA (C. perfringens Enterotoxin Test—TechLab). PCR testing on feces has been used to identify the gene that
encodes for enterotoxin production (cpe). Using a combination of immunodetection and PCR appears to offer optimal diagnostic
sensitivity.8 The Gastrointestinal Laboratory at Texas A&M University offers the PCR test for the cpe gene, and information regarding
sample handling and submission is provided at http://www.cvm.tamu.edu/gilab/assays/C.%20perfringens%20enterotoxin%20gene.shtml.
Figure 4. A fecal smear showing numerous endospores of Clostridium perfringens (modified Wright's stain; 1,000X). (Photo courtesy of Debra Zoran, DVM, DACVIM.)
Additional diagnostic tests for any cat with chronic diarrhea should include a serum chemistry profile, a complete blood count
including white blood cell differential, an electrolyte panel, a urinalysis, and feline leukemia virus antigen and feline
immunodeficiency virus antibody tests. Thyroxine concentrations should be measured in any cat over 7 years of age or with
clinical signs suggestive of hyperthyroidism.
This laboratory data helps determine the severity of systemic disease and may identify potential extragastrointestinal causes
of chronic diarrhea. Hypoalbuminemia is suggestive of serious GI disease and can be noted with alimentary lymphoma or fungal
enteritis.9 Markedly increased hepatic enzyme activity (e.g. alanine transferase, alkaline phosphatase) or bilirubin concentration may indicate concurrent or secondary hepatopathies.
The peripheral eosinophil count is often elevated in cats with parasitic, fungal, or eosinophilic enteritis. Anemia along
with decreased total protein and increased blood urea nitrogen concentrations may suggest GI blood loss.