Page 1530 - Small Animal Internal Medicine, 6th Edition

1502 PART XIV Infectious Diseases

CHAPTER 97
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Polysystemic Mycotic

Infections

BLASTOMYCOSIS disease, skin disease, depression, lameness, and syncope are
the most common presenting complaints.
Etiology and Epidemiology Fever occurs in approximately 40% of affected dogs.
Blastomyces dermatitidis is a saprophytic yeast found primar- Interstitial lung disease and hilar lymphadenopathy result
ily in the Mississippi, Missouri, and Ohio River valleys; the in cough, dry and harsh lung sounds, and dyspnea; hyper-
mid-Atlantic states; and southern Canada. An extracellular trophic osteopathy occurs in some dogs. Infection of the
yeast form (5-20 µm in diameter) with broad-based budding nasal cavity, the nasopharynx, and the retrobulbar area
develops in the vertebrate host (Table 97.1). The infectious occurs rarely and can extend intracranially. Dyspnea from
mycelial phase occurs in the soil and in culture. chylothorax caused by cranial vena cava syndrome has
Blastomycosis develops most frequently in areas exposed been described. Valvular endocarditis occurs as well, and
to high humidity, fog, excavation sites, and sandy, acidic conduction disturbances from myocarditis are detected in
soils near bodies of water. Potential for disease may vary some dogs with cardiac blastomycosis. Lymphadenopathy
with the virulence of the field strain, the inoculum dose, and cutaneous or subcutaneous nodules, abscesses, plaques,
and the immune status of the host. Most clinical cases occur or ulcers occur in 20% to 40% of infected dogs. Spleno-
from point source exposure; multiple cases are diagnosed megaly is common. Lameness from fungal osteomyelitis of
in an area, and clusters of infection in people and dogs the spine or appendicular skeleton occurs in approximately
have been reported. Seasonal, weather, and environmental 30% of dogs with blastomycosis. Infection of the testes, pros-
variables influence prevalence rates. Transmission is from tate, urinary bladder, mammary glands, and kidneys occurs
inhalation or contamination of open wounds with spores rarely.
from the environment. Nasal culture failed to identify the Ocular manifestations are recognized in approximately
fungus on samples collected from 110 clinically normal dogs 30% of dogs with blastomycosis; anterior uveitis, end-
living in an endemic area, suggesting colonization of this site ophthalmitis, posterior segment disease, and optic neuritis
is not common (Varani et al., 2009). After inhalation, the occur. Cataracts can result from chronic inflammation or
organism probably replicates in the lungs initially and then rupture of the lens capsule. Fungal infections of the CNS
spreads hematogenously to other tissues, including the skin were recently reviewed (Bentley et al., 2018). Blastomycosis
and subcutaneous tissues, eyes, bones, lymph nodes, external of the CNS often is an intracranial mass or a cause of ven-
nares, brain, testes, nasal passages, prostate, liver, mammary triculitis. Depression and seizures from diffuse or multifocal
glands, vulva, and heart. However, central nervous system CNS involvement occur in some dogs.
(CNS) disease may result from extension from the nasal Blastomycosis can occur in any cat but is most common
cavity. The organism can be swallowed and passed in feces. in young males. Both cats housed indoors and cats allowed
Incomplete clearance of the organism by individuals with outdoors can develop disease. Infected cats develop respira-
poor cell-mediated immune responses results in pyogranu- tory tract disease, CNS disease, regional lymphadenopathy,
lomatous inflammation in affected organs, which can cause dermatologic disease, ocular disease, gastrointestinal tract
clinical signs of disease. Subclinical infection is believed to disease, and urinary tract disease. Pleural or peritoneal effu-
be uncommon in dogs and cats. sion resulting in dyspnea or abdominal distension occurs
in some cats. Ocular disease usually involves the posterior
Clinical Features segment.
Large-breed, young, male, sporting dogs are infected most
commonly by B. dermatitidis most likely because of an Diagnosis
increased chance for exposure to the organism. Anorexia, Hematologic abnormalities commonly identified in dogs
cough, dyspnea, exercise intolerance, weight loss, ocular or cats with blastomycosis are normocytic normochromic

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