F

F



Fecal Culture



DEFINITION


Analysis of feces for enteric bacterial pathogens



TYPICAL NORMAL RANGE


Reported as negative or degree (slight, moderate, heavy) of growth of specific pathogens



PHYSIOLOGY


Chronic diarrhea, especially in patients with signs of systemic disease (intermittent or persistent fever, leukocytosis or leukopenia) or melena, may be due to enteric bacterial infection. Laboratory conditions enhance growth of pathogens, allowing isolation of bacterial colonies and their identification by morphologic features and chemical tests.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Enteric infection. Common enteric pathogens include Salmonella spp., Clostridium spp., Shigella spp., Yersinia spp., Escherichia coli, and Campylobacter spp. Culture results that include only normal enteric organisms are not helpful in identifying enteric diseases resulting from their overgrowth. In such cases, underlying causes for clinical disease including immune deficiencies, and primary viral infections should be considered.


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Request specific antibiotic sensitivity.


IMPORTANT INTERSPECIES DIFFERENCES: Bacterial enteritis is an uncommon but serious disease in dogs and very rare in cats.



SPECIMEN AND PROCESSING CONSIDERATIONS


DRUG EFFECTS ON LEVELS: Low-level antibiotic therapy may inhibit culture growth.


LAB ARTIFACTS THAT MAY INTERFERE: False-negative results: delay in setting up culture, contamination or overgrowth of normal flora, failure to notify lab of suspected fastidious pathogens requiring special handling, exposure of anaerobes to oxygen


SPECIMEN: Fresh feces in sterile container. If shigellosis, campylobacteriosis, or clostridial infection is suspected, special transport media may be needed, depending on transport time to reference laboratory. Contact laboratory to obtain appropriate transport media.


RELATIVE COST: $$



PEARLS



• Most enteric pathogens cause disease in humans; specimen-handling precautions are necessary to reduce risk of zoonosis.

• Much overlap exists between bacterial flora of dogs with enteritis and normal dogs. Identification of certain fecal bacteria does not necessarily indicate a cause-and-effect relationship.

AUTHOR: LOIS ROTH-JOHNSON



Fecal Flotation



DEFINITION


Screening test for detection of parasitic ova and larvae in feces



TYPICAL NORMAL RANGE


Reported as negative or positive with species identification



PHYSIOLOGY


Flotation of parasitic ova and cysts is promoted in solutions with a greater osmolarity than water. Fecal specimens are mixed with saturated sugar or zinc sulfate solution in a small cylinder topped with a coverslip. After allowing time for ova or cysts to rise to the surface, the coverslip is examined microscopically.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Gastrointestinal or, less commonly, respiratory parasitic infection. Ova of ascarids, hookworms, and flukes. Coccidia, tapeworm segments, and protozoa may be identified.


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Positive test result is definitive.


CAUSES OF ABNORMALLY LOW LEVELS: Intermittent shedding of ova


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: Serial fecal analyses, empirical anthelmintic treatment, further diagnostic testing of gastrointestinal or respiratory system



SPECIMEN AND PROCESSING CONSIDERATIONS


DRUG EFFECTS ON LEVELS: Anthelmintic treatment may decrease parasite burden.


LAB ARTIFACTS THAT MAY INTERFERE: Freezing or delayed specimen processing distorts or destroys ova. decreasing detection.


SPECIMEN: Fresh feces (<24 hours, room temperature or refrigerated) in dry container. If a delay in processing is anticipated, a solution of feces (one part) and sodium acetate/acetic acid formalin (three parts) may be submitted. To prepare solution, combine 1.5 g sodium acetate, 2 mL glacial acetic acid, 4 mL 40% formaldehyde, and 92.5 mL water. Indicate that specimen has been diluted. RELATIVE COST: $



PEARLS



• Diarrhea may decrease ova concentration.

• Ova shedding is intermittent, so a single negative test does not rule out infection. Serial testing (at least three) should be done if parasitic disease is suspected.

AUTHOR: LOIS ROTH-JOHNSON



Feline Coronavirus Testing



DEFINITION


Feline coronavirus (FCV) infection refers to two distinct entities: feline infectious peritonitis (FIP) and feline enteric corona-viral (FECV) enteritis. FIP is a systemic viral disease of high mortality characterized by insidious onset, fever, disseminated pyogranulomatous inflammation, and in some cases, proteinaceous exudative effusions in body cavities (“wet form”). FECV causes mild transient diarrhea and/or vomiting and, less commonly, chronic or severe diarrhea. A positive titer does not distinguish between these two entities.



TYPICAL NORMAL RANGE


Consult with laboratory conducting the test.



PHYSIOLOGY


In FIP FCV is ingested and then replicates in intestinal epithelial cells and probably tonsils and oropharynx. The virus infects macrophages, with subsequent extension to multiple tissues. Antiviral antibodies are produced such that immune complexes form and are deposited in blood vessels of serosal surfaces, uvea, kidney, liver, and other tissues. A pyogranulomatous response ensues. Proteinaceous abdominal or thoracic effusion results from increased vascular permeability. FIP-type coronavirus is thought to represent a spontaneous mutation of FCV that occurs in vivo in certain individual cats.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Positive FCV titer indicates nonspecific exposure to any of the following: FIP coronavirus, feline enteric coronavirus, other coronaviruses, or FIP vaccine. Serology is therefore nonspecific.


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Correlate with history, physical exam findings, and other laboratory data. Consider cytologic evaluation, A: G ratio, PCR, or IFA on effusion fluid, all of which are supportive but not definitive (none of these tests differentiates between FIP coronavirus and enteric coronavirus). Quantitative mRNA PCR Multi-Test on blood, feces, and effusion or tissue aspirate may differentiate FIP-coronavirus from enteric coronavirus. Histopathologic analysis of biopsy or necropsy tissue is generally required for definitive diagnosis.


CAUSES OF ABNORMALLY LOW LEVELS: False-negative serologic test results may arise from peracute infection, low antibody level, lack of antibody production, or antibody bound within immune complexes.


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: If FIP is still suspected, consider same diagnostic steps as if test is positive.



SPECIMEN AND PROCESSING CONSIDERATIONS


LAB ARTIFACTS THAT MAY INTERFERE: PCR: false-positive results due to specimen contamination; false-negative results due to degradation of nucleic acids via improper sample handling and storage


SPECIMEN: One mL serum (red-top tube) for serology. Samples for serologic analysis can be stored up to 4 days at refrigerator temperature or for longer periods at −20○C without loss of antibody. For mRNA PCR Multi-Test, submit (at room temperature) up to 700 μL of EDTA blood (lavender-top tube) and/or sample fluid (body cavity fluid, CSF, joint fluid), tissue or fecal swab, or piece of tissue not larger than 5 mm in diameter in special sample buffer (obtained from Auburn University, http://www.vetmed.auburn.edu/molecular-diagnostics/faq). RELATIVE COST: $$ (IFA serum antibody, PCR), $$$ (IFA tissue)



PEARLS


A negative titer alone does not rule out FIP, nor does a positive titer alone indicate FIP. Multiple sampling and evaluation via the FIP mRNA PCR test increases sensitivity over single sampling, and detection of FIP mRNA via PCR in any extraintestinal sample confirms FIP with nearly 100% specificity.


AUTHOR: PATTY J. EWING



Feline Immunodeficiency Virus Testing



DEFINITION


Feline immunodeficiency virus (FIV) is a retrovirus (lentivirus) that attacks the immune system of cats and results in progressive immunosuppressive disease.



TYPICAL NORMAL RANGE


Reported as positive or negative



PHYSIOLOGY


FIV is inoculated via saliva or blood from bite wounds. There are three stages of infection. Acute phase: FIV initially infects T lymphocytes and salivary glands, with subsequent spread to other mononuclear cells; cats may have fever, leukopenia, and lymphadenopathy. Subclinical phase: cats may be without clinical signs for years. Chronic phase: progressive immunosuppression with development of a wide variety of clinical disorders, including stomatitis/gingivitis, anemia and leukopenia, neurologic signs, enteritis, weight loss, and opportunistic infections. A cat may have no clinical signs for years, owing to a prolonged subclinical phase that follows acute infection. Available tests measure circulating FIV antibody levels, not viral antigen. The extended natural course of lentivirus infections makes the presence of antibody essentially equivalent to infection (exceptions: maternal antibody, vaccination).



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Screening test: ELISA (SNAP) or rapid immunomigration assay—positive indicates possible exposure to FIV or FIV vaccine; positive or equivocal result requires confirmatory testing. Due to maternally transferred antibody, FIV testing of kittens <6 months of age is unreliable (false positives) and is not recommended.


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Confirmatory tests: Western blot or IFA. Positive Western blot or IFA indicates maternal antibody (kittens <6 months old) or exposure to FIV or the vaccine. PCR test may be a useful test in the future for differentiating vaccine exposure from true infection; however, currently available tests vary markedly in their diagnostic accuracy and should be interpreted with caution.


CAUSES OF ABNORMALLY LOW LEVELS: Negative ELISA indicates lack of exposure or acute infection.


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: If clinical signs suggest FIV infection, retest in 4-12 weeks.



SPECIMEN AND PROCESSING CONSIDERATIONS


LAB ARTIFACTS THAT MAY INTERFERE: PCR: false-positive results due to contamination of samples; false-negative results due to degradation of nucleic acids via improper sample handling and storage. Up to 50% false-negative results due in part to insufficient primer and probe sequences (many strain variations of FIV present). SPECIMEN


• ELISA: 1 mL serum (red-top tube) or plasma (lavender- or green-top tube)

• Western blot or IFA: 1 mL of serum (red-top tube)

RELATIVE COST: $$ (IFA, ELISA); $$$ (Western blot)


AUTHOR: PATTY J. EWING



Feline Leukemia Virus (ELISA)



DEFINITION


Feline leukemia virus (FeLV) is a retrovirus of cats that causes hematopoietic neoplasia, immunosuppression, and/or anemia.

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on F

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