Page 326 - Small Animal Internal Medicine, 6th Edition

298 PART II Respiratory System Disorders

The hosts of lung parasites generally cough up and canine influenza are discussed further in Chapter 22. Serum
swallow the eggs or larvae, which then are passed in the feces antigen tests for Cryptococcus (see Chapter 97) and adult
VetBooks.ir to infect the next host or an intermediate host. Fecal exami­ heartworms are also available (see Chapter 10). Antibody
tests for dirofilariasis are available and are used primarily
nation for eggs or larvae is a simple, noninvasive tool for the
diagnosis of such infestations. However, because shedding is
Chapter 10).
intermittent, parasitic disease cannot be included solely on to support the diagnosis of feline heartworm disease (see
the basis of negative fecal examination findings. Multiple (at
least three) examinations should be performed in animals
that are highly suspected of having parasitic disease. If pos­ URINE ANTIGEN TESTS
sible, several days should be allowed to elapse between col­
lections of feces. Urine antigen tests for the detection of Histoplasma and Blas-
Routine fecal flotation can be used to concentrate eggs tomyces antigens are available. The test for Blastomyces is
from C. aerophila. High­density fecal flotation (specific more sensitive than serum antibody testing by agar gel
gravity [s.g.], 1.30 to 1.35) can be used to concentrate P. immunodiffusion for the diagnosis of blastomycosis (Spector
kellicotti eggs. Sedimentation techniques are preferred for et al., 2008). See Chapter 97 for further discussion.
concentrating and identifying P. kellicotti eggs, particularly
if few eggs are present. Larvae are identified through the use
of the Baermann technique. However, O. osleri larvae are POLYMERASE CHAIN REACTION TESTS
insufficiently motile for reliable identification with this tech­
nique, and zinc sulfate (s.g., 1.18) flotation is recommended. Molecular diagnostic tests are available for identification of
Even so, false­negative results are common in cases with O. a wide range of individual respiratory pathogens. Panels of
osleri. tests are commercially available for multiple agents com­
All of these techniques can be readily performed in­house monly involved in acute respiratory tract infection in dogs
at minimal expense, but the infrequent identification of or cats. Specimens that can be tested include swabs from the
respiratory parasites in small­animal patients makes submis­ oropharynx, nasal cavity, or conjunctiva; tracheal wash or
sion of feces to an external laboratory with greater experi­ bronchoalveolar lavage specimens; airway brushings; and
ence in organism identification appealing. However, timing tissue. Best results are obtained when the timing and the site
should be carefully arranged to ensure that fresh feces are of collection are chosen on the basis of the pathophysiology
available for prompt evaluation by laboratory personnel. of the target organism. For collection of material by swab,
Toxoplasma gondii occasionally causes pneumonia in polyester swabs should be used. Consultation with the diag­
dogs and cats. Dogs do not shed Toxoplasma organisms in nostic laboratory is recommended for specimen collection
the feces, but cats may. However, the shedding of eggs is part and handling to maximize results.
of the direct life cycle of the organisms and does not correlate
with the presence of systemic disease resulting from the indi­
rect cycle. Infection is therefore diagnosed by the finding of TRACHEAL WASH
tachyzoites in pulmonary specimens or indirectly on the
basis of serologic findings. Indications and Complications
Migrating intestinal parasites can cause transient pulmo­ Tracheal wash can yield valuable diagnostic information in
nary signs in young animals. Migration most often occurs animals with cough or respiratory distress resulting from
before the mature adults develop in the intestine, thus eggs disease of the airways or pulmonary parenchyma and in
may not be found in feces. Migration of Toxocara cati has animals with vague presenting signs and pulmonary abnor­
been implicated as a cause of idiopathic feline bronchitis in malities detected on thoracic radiographs (i.e., most animals
adult cats, but no practical means of diagnosis exists (Dillon with lower respiratory tract disease). Tracheal wash is gener­
et al., 2013). ally performed after results of the history, physical examina­
tion, thoracic radiography, and other routine components of
the database are known.
SEROLOGY Tracheal wash provides fluid and cells that can be used to
identify diseases involving the major airways while bypass­
Serologic tests can detect a variety of pulmonary pathogens. ing the normal flora and debris of the oral cavity and pharynx.
Antibody tests provide only indirect evidence of infection, Representative specimens are often obtained from patients
however. In general, they should be used only to confirm a with disease of the small airways (e.g., bronchitis) or alveoli
suspected diagnosis, not to screen for disease. Whenever pos­ (e.g., bacterial pneumonia or aspiration pneumonia) because
sible, identification of infectious organisms is the preferred diagnostic material is carried to the major airways by muco­
method of diagnosis. Tests available for common pulmo­ ciliary clearance, cough, or the extension of disease (Table
nary pathogens include those for Histoplasma, Blastomyces, 20.2). The fluid obtained is evaluated cytologically and
Coccidiodomyces, Toxoplasma, and feline coronavirus. These microbiologically and therefore should be collected before
tests are discussed fully in Chapter 97. Antibody tests for antibiotic treatment is initiated, whenever possible.