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Blastomycosis 121

Blastomycosis Bonus Material Client Education
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VetBooks.ir BASIC INFORMATION DIAGNOSIS Diseases and Disorders

DISEASE FORMS/SUBTYPES
Definition Clinical Presentation Diagnostic Overview
Systemic mycotic infection caused by the Disseminated disease is most common (two- Most often, characteristic lesions on thoracic
dimorphic fungus Blastomyces dermatitidis, thirds of cases). The pulmonary form of radiographs of a patient that has been in an
affecting many mammalian species, including the disease accounts for one-third of cases. endemic area alert the clinician to the possibility
humans, dogs, and cats Cutaneous, ocular, and osseous forms also are of fungal infection. Identification of organisms
reported. by cytology or histopathology is ideal. A urine
Epidemiology antigen test for blastomycosis is more sensitive
SPECIES, AGE, SEX HISTORY, CHIEF COMPLAINT than serologic testing.
• Occurs most often in dogs, less commonly Any combination of anorexia, weight loss,
in cats cough, dyspnea, exercise intolerance, ocular Differential Diagnosis
• Often occurs in young, large-breed, changes, lameness, skin lesions, and neurologic • Pulmonary form: metastatic neoplasia;
male dogs; dogs 2 to 4 years of age are signs is possible. bacterial or viral pneumonia, interstitial lung
overrepresented disease
PHYSICAL EXAM FINDINGS • Bone form: bacterial osteomyelitis, primary
GENETICS, BREED PREDISPOSITION Clinical signs depend on organ systems affected: or metastatic bone tumors
Sporting and working breed dogs are at • Fever, lethargy, emaciation, lymphadeno- • Cutaneous form: bacterial, fungal, parasitic,
increased risk. megaly autoimmune dermatitis
• Pulmonary involvement: harsh lung sounds; • Other systemic mycoses
RISK FACTORS cough; dyspnea at rest
• Outdoor, roaming dogs in endemic areas • Ocular changes: signs of uveitis (p. 1023), Initial Database
living within 400 meters of water are at chorioretinitis with retinal detachment, CBC:
increased risk. endophthalmitis, corneal edema, glaucoma • Mild normocytic, normochromic anemia
• Exposure to sandy, acidic soil disrupted • Skin lesions (nasal planum, face, nail beds): • Moderate leukocytosis (17,000-30,000 white
by construction involving earth moving or subcutaneous abscesses, ulcerated draining blood cells/mcL), left shift, lymphopenia
excavation lesions, or granulomatous proliferative Serum biochemistry panel:
lesions. Large abscesses are more common • Hyperglobulinemia
CONTAGION AND ZOONOSIS in cats than in dogs. • Hypoalbuminemia
• Common-source exposure is possible, but • Bone involvement: lameness due to fungal • Hypercalcemia (occasionally)
true zoonosis is rare because yeast form is osteomyelitis, paronychial inflammation Thoracic radiographs:
too large to be inhaled. Exception remains • Neurologic signs may include abnormal • Diffuse, nodular interstitial and bronchoin-
inoculation of the organism (e.g., needlestick mentation, paresis, vestibular ataxia, cranial terstitial lung patterns common
injuries, cut during necropsy of infected nerve deficits, and decreased to absent • Solitary to multiple nodules may be seen.
animal). postural responses. • Tracheobronchial lymphadenopathy seen less
• Risk of aerosolization and possible transmis- often than with histoplasmosis
sion from culture samples Etiology and Pathophysiology • Less commonly: pleural effusion, pneumo-
• B. dermatitidis is a dimorphic fungus that mediastinum
GEOGRAPHY AND SEASONALITY exists in the mycelial form in the soil and • Radiographs of bones: osteolytic or periosteal
• B. dermatitidis is found in North America, as a yeast in tissues. proliferation with soft-tissue swelling
Africa, and Central America. Endemic areas ○ The mycelial form grows in warm, moist,
include the Mississippi, Missouri, Tennessee, sandy soil rich in organic matter, especially Advanced or Confirmatory Testing
Ohio, and St. Lawrence River valleys; mid- in manure-enriched soil, and produces • Identification of the organism in more than
Atlantic states; northern California, Pacific conidia that are released into the air. Soil half of the cases by cytologic examination
Northwest, and the Canadian provinces of disruption exposes organisms from deep of lymph node aspirates, draining exu-
Alberta, Manitoba, Ontario, Quebec, and within the soil. dates, skin impression smears, or vitreous
Saskatchewan. • The route of infection is by inhalation of aspirates
• No seasonal distribution in the United mycelial spores that enter the terminal ○ A thick-walled, broad-based budding yeast
States airways from the environment. is characteristic of Blastomyces.
• The specific location of the fungus in soil is • At body temperature, the conidia become • Lung aspirates (p. 1113) often identify the
unknown; the fungal colonies are not grossly yeasts and establish an infection in the lungs organism. Tracheal wash is less sensitive
visible and are difficult to isolate from the that may then spread throughout the body than a lung aspirate, but sensitivity may
environment. by blood and lymphatics. be increased by bronchoalveolar lavage
• A microfocus model for the ecology of B. • Organisms cause a pyogranulomatous inflam- (pp. 1073 and 1074).
dermatitidis suggests that environmental mation with a predilection for the skin, eyes, • Urine Blastomyces antigen test has > 90%
pockets of fungal growth occur when a bones, lymph nodes, subcutaneous tissues, sensitivity and is the preferred approach when
suitable combination of soil type and mouth, nares, brain, mammary tissues, organisms are not found. The Blastomyces
moisture is present. Rain, physical disruption prostate, and testes. urine antigen test is done by MiraVista Labs
of soil, or both may promote release of • Cats are less commonly infected but develop (Indianapolis, IN, www.miravistalabs.com/
spores. a similar spectrum of lesions as dogs and veterinary-testing/blastomycosis/). A nega-
• Proximity of the face to soil increases likeli- may also have pharyngeal lesions. Central tive antigen test does not exclude infection;
hood of inhalation/infection. nervous system (CNS) involvement is more cross-reactivity with Histoplasma is seen
common in cats. (p. 1365).

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