Page 1460 - Small Animal Internal Medicine, 6th Edition

1432 PART XIV Infectious Diseases

fungi occurs in vivo and is not zoonotic; the mycelial phase these techniques are more sensitive and specific than histo-
of Blastomyces, Coccidioides, and Histoplasma grows in pathologic techniques and are comparable with culture. For
VetBooks.ir culture and will infect human beings. Thus in-house culture example, focal feline infectious peritonitis granulomatous
disease can be documented by immunohistochemical stain-
for these agents is not recommended.
Viral agents can be isolated from tissues or secretions at
(Merifluor Cryptosporium/Giardia, Meridian Bioscience
some laboratories. Contact the laboratory before submitting ing (see Chapter 96). A fluorescent antibody-based assay
samples. Samples should be collected aseptically as for bac- Inc., Saco, ME) for the detection of Giardia spp. cysts and
teria, placed in transport media, and immediately refriger- Cryptosporidium spp. oocysts in feces is commonly used to
ated to inhibit bacterial growth. The samples should be aid in the diagnosis of these infections in dogs and cats
transported to the laboratory on cold packs but not frozen. (Mekaru et al., 2007).
IMMUNOLOGIC TECHNIQUES MOLECULAR DIAGNOSTICS
Infectious agents or their antigens can be detected in body A number of different techniques can be used to amplify
fluids, feces, cells, or tissues by using immunologic tech- the DNA or RNA of infectious agents (Veir and Lappin,
niques. In general, polyclonal or monoclonal antibodies 2010). Polymerase chain reaction is used frequently for
against the agent in question are used in a variety of differ- DNA amplification (Fig. 91.7). With a reverse transcriptase
ent test methods, including direct fluorescent antibody assay step, RNA is converted to DNA; therefore the technique
with cells or tissue, agglutination assays, and enzyme-linked
immunosorbent assay (ELISA). Sensitivities and specificities
vary by test but are generally high for most assays. Positive
results with these tests generally prove infection; this is in
contrast to antibody detection procedures, which only docu-
ment exposure to an infectious agent. Contact the laboratory
for details concerning specimen transport before collection.
Commercially available assays for the detection of anti-
gens of Dirofilaria immitis, Cryptococcus neoformans, Blasto-
myces dermatitidis, and feline leukemia virus (FeLV) are used
most frequently with blood from small animal patients. The
Cryptococcus neoformans latex agglutination procedure can
also be performed on aqueous humor, vitreous humor, and
CSF (see Chapter 97).
Parvovirus Giardia spp. antigen detection procedures are
available for use with feces of dogs and cats. Parvovirus
assays detect both canine and feline parvovirus antigen and
may be affected transiently by administration of modified-
live vaccines (Abd-Eldaim, 2009; Freisl et al., 2017). Both
CPV2c and CPV2b are detected by currently available assays
(Markovich et al., 2012). Most Giardia antigen tests mar-
keted for use with human or pet feces detect the Giardia
assemblages that infect dogs or cats (Rishniw et al., 2010).
Samples are occasionally antigen positive but cyst negative
on fecal flotation. In this situation either the antigen test is
falsely positive or the fecal flotation is falsely negative, and
both tests should be repeated on a new fecal sample. Alter-
nately, the feces can be evaluated further for Giardia cysts by
fluorescent antibody assay (next paragraph) or polymerase
chain reaction. None of the currently available ELISA-based
Cryptosporidium parvum antigen tests marketed for use with
human feces consistently detects Cryptosporidium felis or
Cryptosporidium canis and should therefore not be used with
feces from dogs and cats. FIG 91.7
Immunocytochemistry and immunohistochemistry tech- Photograph of a polymerase chain reaction assay for
niques are widely available for the documentation of a variety hemoplasmas showing the two different band sizes that help
differentiate species: Mycoplasma haemofelis (Lane 2) and
of infectious diseases. These procedures are particularly Candidatus M. haemominutum (Lane 4). Lane 1 is a base
valuable for the detection of viral diseases, detection of pair ladder, and Lane 3 is a negative sample. In this assay,
agents present in small numbers, and for differentiation Candidatus M. turicensis is included in the M. haemofelis
among agents with similar morphologic features. In general, amplicon.