Page 1531 - Small Animal Internal Medicine, 6th Edition

CHAPTER 97 Polysystemic Mycotic Infections 1503

TABLE 97.1
VetBooks.ir Morphologic Appearance of Systemic Canine and Feline
Fungal Agents
AGENT CYTOLOGIC APPEARANCE

Blastomyces Extracellular yeast, 5-20 µm in
dermatitidis diameter; thick, refractile,
double-contoured wall; broad-
based bud; routine stains are
adequate
Cryptococcus spp. Extracellular yeast, 3.5-7.0 µm in
diameter; thick, unstained
capsule; thin-based bud; violet
color with light-red capsule with FIG 97.1
Gram stain; unstained capsule Miliary interstitial lung pattern consistent with blastomycosis
with India ink in a dog. (Courtesy Dr. Lynelle Johnson, College of
Coccidiodes spp. Extracellular spherules (20-200 µm Veterinary Medicine, University of California, Davis.)
in diameter) containing
endospores; deep red to purple
double outer wall with bright red
endospores with PAS stain
Histoplasma Intracellular yeast in mononuclear
capsulatum phagocytes, 2-4 µm in diameter,
basophilic center with lighter
body with Wright stain
Sporothrix Intracellular yeast in mononuclear
schenckii phagocytes, 2-3 µm × 3-6 µm in
diameter; round, oval, or
cigar-shaped

PAS, Periodic acid–Schiff.

nonregenerative anemia, lymphopenia, neutrophilic leu-
kocytosis with or without a left shift, and monocytosis.
Hypoalbuminemia and hyperglobulinemia (i.e., polyclonal FIG 97.2
gammopathy) caused by chronic inflammation are common Cytologic appearance of the budding yeast, Blastomyces
serum biochemical abnormalities; hypercalcemia occurs dermatitidis. The organism is 5 to 20 µm in diameter with a
thick, refractile, double-contoured wall. (Courtesy Dr. Dennis
rarely in dogs. Most infected dogs and cats with respiratory Macy, College of Veterinary Medicine and Biomedical
disease have diffuse, miliary, or nodular interstitial lung pat- Sciences, Colorado State University.)
terns and intrathoracic lymphadenopathy on thoracic radio-
graphs (Fig. 97.1); single masses and pleural effusion from
chylothorax sometimes occur. Alveolar lung disease occurs successful treatment. False-negative results can occur in
in some cats. Bone lesions induced by blastomycosis are lytic animals with peracute infection, immunosuppression, or
with a secondary periosteal reaction and soft tissue swell- advanced infection that overwhelms the immune system;
ing. Intracranial blastomycosis generally reveals evidence of many cats with blastomycosis are seronegative.
extension from the nasal cavity on diagnostic imaging but Detection of the organism in a clinically ill animal with
solitary CNS granulomas do occur (Bentley et al., 2018). the appropriate presentation can give a definitive diagnosis
Serum antibodies develop in some infected animals; agar of blastomycosis. The organism can be demonstrated by
gel immunodiffusion (AGID) or a commercially available cytology, histopathology, culture, antigen test, or amplifica-
canine assay (www.miravistalabs.com) is frequently used. tion of specific DNA by polymerase chain reaction (PCR)
Because blastomycosis rarely causes subclinical infection, assay. Impression smears from skin lesions and aspirates
positive serum antibody assay results combined with appro- from enlarged lymph nodes and focal lung lesions usually
priate clinical signs and radiographic abnormalities allow reveal pyogranulomatous inflammation and organisms that
presumptive diagnosis if the organism cannot be demon- can usually be seen at low power (Fig. 97.2). Recovery of
strated. Antibody titers do not always revert to negative after organisms from urine is less consistent. Bronchoalveolar