Clinical problem and differentials
Vomiting is the forceful ejection of stomach and proximal duodenal contents through the mouth. Vomiting can be induced by
vestibular, vagal, chemoreceptor trigger zone, or direct input to the emetic center. Diarrhea is a characterized by increased
frequency of defecation, increased fluid content of the stool, or increased volume of stool. Markedly increased frequency
of defecation, small volume stools, tenesmus, urgency, hematochezia, and mucus are consistent with large bowel diarrhea.
Slight increase in frequency of defecation, large volume, melena, steatorrhea, and polysystemic clinical signs are more consistent
with small bowel diarrhea. Mixed bowel diarrhea is a combination of characteristics or clinical signs. Gastrointestinal
(GI) signs can be the result of primary diseases of the GI system or secondary GI diseases. The secondary GI diseases are
generally those of the kidneys, liver, pancreas (pancreatitis or exocrine pancreatic insufficiency), endocrine system (hypoadrenocorticism;
diabetic ketoacidosis; hyperthyroidism), or central nervous system. Differential diagnoses for primary GI diseases are often
grouped into obstruction (masses, foreign body, and intussusception), dietary intolerance, drugs/toxins (garbage gut), inflammatory
gastric and bowel diseases, neoplasia, infectious diseases, and parasites. The primary bacteria associated with gastrointestinal
tract disease in cats include Salmonella spp., Campylobacter jejuni, Clostridium perfringens, Helicobacter spp., bacterial overgrowth syndrome, bacterial peritonitis, and bacterial cholangiohepatitis. The primary viral agents include
feline coronaviruses, feline leukemia virus, feline immunodeficiency virus, and feline panleukopenia virus. The primary nematodes
Strongyloides cati, Dirofilaria immitis (vomiting), Toxocara cati, Toxascaris leonina, Ollulanus tricuspis, and Physaloptera spp. Enteric protozoans include Giardia spp., Cystoisospora spp., Cryptosporidium spp., Entamoeba histolytica, and Tritrichomonas foetus. The cestodes Taenia, Dipylidium, and Echinococcus generally cause subclinical infection.
Diagnostic procedures for infectious diseases
Liquid feces or feces that contains large quantities of mucus should be microscopically examined immediately for the presence
of protozoal trophozoites, including those of Giardia spp. and Tritrichomonas foetus. A direct saline smear can be made to potentiate observation of these motile organisms. The amount of feces required to
cover the head of a match is mixed thoroughly with one drop of 0.9% NaCl. Following application of a coverslip, the smear
is evaluated for motile organisms by examining it under 100X magnification. The sample should be fresh. The material for
evaluation should be collected from the surface of the fecal material, preferably mucous if present. Alternately, a rectal
scraping can be used.
A thin smear of feces should be made from all cats with large or small bowel diarrhea. Material should be collected by rectal
swab if possible to increase chances of finding white blood cells. A cotton swab is gently introduced 3-4 cm through the
anus into the terminal rectum, directed to the wall of the rectum, and gently rotated several times. Placing a drop of 0.9%
NaCl on the cotton swab will facilitate passage through the anus, but not adversely affect cell morphology. The cotton swab
is rolled on a microscope slide gently multiple times to give areas with varying smear thickness. Following air drying, the
slide can be stained. White blood cells and bacteria morphologically consistent with Campylobacter jejuni or Clostridium perfringens can be observed after staining with Diff-Quick or Wright's-Giemsa stains. Histoplasma capsulatum or Prototheca may be observed in the cytoplasm of mononuclear cells. Methylene blue in acetate buffer (pH 3.6) stains trophozoites of the
enteric protozoans. Iodine stains and acid methyl green are also used for the demonstration of protozoans. Acid-fast or
monoclonal antibody staining of a fecal smear should be performed in cats with diarrhea to aid in the diagnosis of cryptosporidiosis.
Cryptosporidium parvum is the only enteric organism of approximately 4 to 6 µ in diameter that will stain pink to red with acid-fast stain. Presence
of neutrophils on rectal cytology can suggest inflammation induced by Salmonella spp., Campylobacter spp., or Clostridium perfringens; fecal culture is indicated in these cases. Fecal enterotoxin measurement should be considered for cats with spore-forming
rods morphologically consistent with C. perfringens.
Cysts, oocysts, and eggs in feces can be concentrated to increase sensitivity of detection. Most eggs, oocysts, and cysts
are easily identified after sugar or zinc sulfate centrifugal flotation. These procedures are considered by many to be optimal
for the demonstration of protozoan cysts, in particular, Giardia spp. and so is a good choice for a routine flotation technique in practice. Sugar centrifugation can be used for routine
parasite evaluation and may be superior to many techniques for the demonstration of oocysts of Toxoplasma gondii and Cryptosporidium spp.. Giardia cysts are distorted by sugar centrifugation but can still be easily identified. Fecal sedimentation will recover most cysts
and ova, but will also contain debris. This technique may be superior to flotation procedures for the documentation of Eurytrema procyonis, the pancreatic fluke. Strongyloides cati larva may be easier to identify after concentration using the Baerman funnel technique.
Culture of feces for Salmonella spp., Campylobacter spp., and Clostridium perfringens is occasionally indicated in small animal practice. Approximately 2-3 grams of fresh feces should be submitted to the laboratory
immediately for optimal results, however, Salmonella and Campylobacter are often viable in refrigerated fecal specimens for 3-7 days. Appropriate transport media should be available through your
laboratory. The laboratory should be notified of the suspected pathogen so appropriate culture media can be used. More than
1 culture may be needed to prove infection. Tritrichomonas foetus can be cultured from feces of cats in general practice using a commercially available kit (InpouchTM, Biomed Diagnostics).
Some Giardia spp. isolated from cats will grow on culture media, but this technique is not generally performed in small animal practice.