Page 442 - Small Animal Internal Medicine, 6th Edition

414 PART III Digestive System Disorders

sensitivity of different techniques varies, making it difficult after onset of clinical signs; therefore, it may be necessary to
to accurately compare results. Finally, blood is often not repeat the test in 2 to 3 days if initial results are negative in
VetBooks.ir distributed homogeneously throughout the feces, and a neg- a dog strongly suspected of having parvoviral infection.
Additionally, although dogs with parvoviral diarrhea ini-
ative result could stem from a sampling error (especially in
animals with lower intestinal tract problems).
substantially during the ensuing 7 to 14 days. A repeatedly
If fecal occult blood analysis is desired, one should feed tially shed large amounts of virus, fecal shedding decreases
the animal a meat-free diet for 3 to 4 days before performing negative test result therefore does not rule out parvoviral
the test. Tests using the reagents benzidine or orthotoluidine infection, but it does necessitate a consideration of other
to detect hemoglobin tend to be very sensitive (and hence acute, febrile gastroenteritides (e.g., salmonellosis). This test
less specific), whereas those using guaiac are less sensitive is particularly valuable if there are epidemiologic consider-
(and thus more specific). A sensitive and specific fluoromet- ations (e.g., breeding kennel).
ric method has been validated in dogs. Repeated testing may ELISAs for detecting a Giardia-specific antigen in human
be necessary to demonstrate intermittent bleeding. (ProSpecT/Microplate ELISA assay for Giardia, Alexon,
Inc.) and canine/feline feces (SNAP Giardia Test, Idexx
BACTERIAL FECAL CULTURE Laboratories) are available. The SNAP Giardia test appears
to be sensitive with good negative predictive value, but it
Fecal culture is seldom indicated in small animals unless a has poor positive predictive value at typical low prevalence
contagious bacterial disease is strongly suspected, and even rates when compared with IFA testing of feces. It has the
then simply finding a “pathogenic” bacteria in an animal’s advantage of being able to be performed in the practice. An
feces does not confirm that it is causing disease. Culture IFA test (MERIFLUOR Cryptosporidium/Giardia direct im-
results must be correlated with clinical signs and the results munofluorescent kit, Meridian Bioscience, Inc.) is probably
of other laboratory tests. The clinician should always contact the most sensitive and specific test for giardiasis but requires
the laboratory before collecting/submitting feces, informing that feces be sent to a commercial laboratory.
them specifically what bacteria to attempt to grow; there are ELISAs for detecting cryptosporidial antigens in feces
specific techniques for collection, submission, and culture (ProSpecT Cryptosporidium Microplate Assay, Meridian
for most fecal pathogens. Fecal culture cannot be used to Diagnostics, Inc. and ProSpecT Cryptosporidium Micro-
diagnose small intestinal antibiotic-responsive enteropathy plate Assay, Remel, Inc.) are more sensitive than routine
(ARE), also called dysbiosis. fecal examinations. Special staining of fecal smears with a
Potential pathogens most commonly cultured from feces modified Ziehl-Neelsen acid-fast technique is also sensi-
from small animals include Clostridium perfringens, Salmo- tive, albeit more labor intensive. An IFA test (MERIFLUOR
nella spp., E. coli, and Campylobacter jejuni. Confirmation Cryptosporidium/Giardia direct immunofluorescent kit,
of toxin production by specific bacteria can be performed Meridian Bioscience, Inc.) is not as sensitive as ELISA when
using PCR techniques or bioassay. Salmonella spp. are best looking for cryptosporidia.
cultured by inoculating at least 1 g of fresh feces into an Assays for bacterial toxins in feces are typically valuable
enrichment medium and subsequently a selective medium for implicating specific bacteria as causing diarrhea in people,
specific for Salmonella spp. Salmonella can also be grown but a positive test in a dog or cat is not prima facia evidence
from colonic mucosa. To culture C. jejuni, very fresh feces it is causing disease. C. difficile in particular is of uncertain
must be inoculated onto selective media and incubated at pathogenic significance in dogs and cats. ELISA tests (C.
approximately 40° C instead of 37° C. If inoculation is to be perfringens Enterotoxin Test, TechLab) and reverse passive
delayed, special transport media should be used, not routine latex agglutination tests (Oxoid PET-RPLA, Unipath Co.)
commercial transport devices (e.g., culturette swabs). for C. perfringens enterotoxin are available, but the results
Candida spp. are occasionally cultured from feces. Growing do not clearly correlate with clinical disease.
Candida is often hard to interpret, but the organisms might PCR testing for antigens in feces has become popular
cause problems in some animals (e.g., those receiving because of its sensitivity and specificity, but finding any of
chemotherapy). numerous agents in feces does not guarantee that the agent
There is a culture technique (InPouch TF, BioMed Diag- is responsible for disease. There are fecal PCR panels that
nostics) for Tritrichomonas blagburni in feline feces. The can detect Giardia, Cryptosporidium, Salmonella, C. perfrin-
culture technique can be done in the practice and appears to gens enterotoxin A, enteric coronavirus, parvovirus, and/
be more sensitive than direct fecal examination but less sen- or distemper virus in canine feces. Likewise there are fecal
sitive than PCR. PCR panels that detect Tritrichomonas blagburni, Giardia,
Cryptosporidium, Toxoplasma gondii, Salmonella, C. perfrin-
ELISA, IFA, AND PCR FECAL ANALYSES gens enterotoxin A, coronavirus, and/or panleukopenia virus
in feline feces. The GI Lab (Texas A&M University) also
ELISA can be used to detect antibodies or antigens. The test offers PCR testing for C. jejuni and C. coli. In all cases, a
for canine parvovirus is very specific. However, parvovirus positive PCR does not guarantee that the agent is producing
may not be excreted in the feces for the first 24 to 48 hours clinical disease.