|FINAL DIAGNOSIS: Disseminated Blastomycosis
in a Dog |
History: A 3-year-old, male German Shepherd dog was
submitted to the Animal Disease Diagnostic Laboratory for
necropsy. Reportedly, the dog had a history of anorexia and
lethargy for three weeks. The dog had been treated with a
course of antibiotics for 10 days with some improvement.
Six days prior to death, the dog reportedly had an Addison’s
crisis and was treated with steroids. The dog was referred
to Purdue University Teaching Hospital. On presentation,
the dog was tachypneic, pale and painful in the abdomen.
Ophthalmology exam revealed retinal granulomas in both eyes.
An aspirate of the popliteal lymph node showed pyogranulomatous
inflammation and Blastomyces dermatitidis organisms.
The dog was humanely euthanized.
Gross Findings: Fibrous tags adhered the right caudal
lung lobe, right middle lung lobe, and pericardial sac to
the parietal pleura of the thoracic cavity. The lungs were
diffusely tan and dark red, mottled and firm on palpation.
Multifocal to confluent, circumscribed, firm, gray, variably-sized
granulomas ranging from 1-10 mm in diameter were disseminated
throughout the lungs. The bronchial lymph nodes were enlarged
and firm and measured approximately 2 x 1.5 cm. The gastric
contents were dark brown to black, liquid, and opaque. The
pyloric antrum of the stomach contained numerous multifocal
mucosal ulcers which ranged from 4-7 mm in diameter. Some
of the ulcers had blood clots adhered to them. Similar mucosal
ulcers were found in the small and large intestine.
Histopathologic Findings: The primary lesion in
the lungs was a multifocal to confluent pyogranulomatous pneumonia.
Numerous intralesional, 10-20μm in diameter, spherical
yeasts with a thick, double refractile cell wall, basophilic
granular central zone, and occasional broad-based budding
consistent with Blastomyces dermatitidis were present.
Bronchial lymph node lesions included pyogranulomatous lymphadenitis
with intralesional Blastomyces dermatitidis. All sections
of brain examined had multifocal pyogranulomatous encephalitis
with intralesional Blastomyces dermatitidis organisms.
The primary morphologic alterations in the right and left
eyes were multifocal sub-retinal accumulations of Blastomyces
dermatitidis organisms with very little inflammatory reaction,
retinal detachment, and small multifocal granulomas in the
choroid. Sections of stomach, duodenum, ileum, and jejunum
contained acute multifocal mucosal ulcers.
Blastomycosis is a systemic mycotic disease caused by the
dimorphic fungus Blastomyces dermatitidis. The disease
primarily affects dogs and humans, but has been reported in
cats, horses, sea lions, lions, wolves, ferrets and polar bears.
Young, male, large breed dogs (especially sporting breeds and
hounds) living near water are at an increased risk. It is generally
restricted to the Mississippi River and OhioRiver basins and
the central Atlantic states.
Most cases of blastomycosis are acquired by
inhalation of aerosolized conidia into the lungs. After inhalation,
the conidia are phagocytized by alveolar macrophages and transform
the mycelial phase to the yeast phase. The yeast stimulates
local cell-mediated immunity which results in a marked suppurative
or pyogranulomatous inflammation. The incubation period varies
from 5-12 weeks.
The acute pulmonary phase of the illness may be asymptomatic
or self-limiting or may result in acute fulminate infection.
The preferred sites of dissemination in the dog are the skin,
eyes, bones, lymph nodes, subcutaneous tissues, external nares,
brain, and testes. Less commonly affected sites are mouth,
nasal passages, prostate, liver, mammary gland, vulva, and
heart. The size of the yeast when it grows at body temperature
prevents it from entering the terminal airway in an aerosol.
Therefore, aerosol transmission of the yeast phase from infected
animals is not possible. However, penetrating wounds can
transmit the disease. Primary cutaneous blastomycosis has
been reported in veterinarians after accidental laceration
while performing a necropsy on a dog with blastomycosis, following
a dog bite from a dog with blastomycosis, and accidental inoculation
with a needle used on a dog with blastomycosis. Cutaneous
blastomycosis is rare in the dog and should be considered
a manifestation of disseminated disease.
The dog appears to be more susceptible to infection than
humans, and serves as a sentinel for the disease. Dogs have
a shorter prepatent period and develop the disease before
people do when exposed at the same time. Most dogs with disseminated
disease are probably immunosuppressed, since the majority
of dogs experimentally infected by exposure of contaminated
soil recover from blastomycosis without treatment.
Clinical signs in dogs with blastomycosis include anorexia,
weight loss, cough, dyspnea, ocular disease, lameness, lymphadenopathy,
and proliferative or draining skin lesions. Signs of disease
usually have been present for a few days to a week but may
have been apparent for several months. In many cases there
has been a history of antibiotic therapy with minimal or temporary
improvement. A majority (85%) of dogs with blastomycosis
have lung lesions, and up to 40% have ocular lesions, the
most common of which is uveitis. Skin lesions are found in
20-40% of dogs with blastomycosis. Bone involvement occurs
in up to 30% of infected dogs. Diffuse lymphadenopathy is
seen in 40% of dogs with blastomycosis.
The yeast organisms range from 5-20 μm in diameter
and are characterized by broad based budding with a thick,
refractile, double-contoured cell wall. Diagnosis is usually
based on finding the characteristic yeasts in cytologic or
histologic preparations. Hematology is usually not helpful
in the diagnosis since complete blood count (CBC) results
are often normal. Radiographic assessment can be helpful
in the diagnosis. Thoracic radiographs often reveal a nodular
interstitial pattern or diffuse interstitial pattern. Serology
should be used diagnostically only when a high degree of suspicion
for Blastomyces exists and repeated attempts have failed
to demonstrate the organisms.
Spontaneous recovery from symptomatic blastomycosis rarely
occurs in dogs but has been reported in people. Therefore,
it is suggested that all cases of symptomatic blastomycosis
in dogs should be treated. Itraconazole is considered the
treatment of choice, except in cases of moderate to severe
hypoxemia when amphotericin B should be considered. Approximately
70-75% of treated cases recover from blastomycosis. Treatment
failure most likely occurs in dogs that are hypoxemic or have
three or more systems involved.
-by Dr. Phaedra Stiles, ADDL Graduate Student
|| Baumgardner EJ and Burdick JS: 1991. An Outbreak of Human
and Canine Blastomycosis. Review of Infectious Diseases 13:
||Krohne SG:2000. Canine Systemic Fungal Infections. Vet Clinics
of North America: Small Animal Practice 30 (5): 1063-1089.
|| Legendre AM, et al: 1981. Canine Blastomycosis: A Review
of 47 Clinical Cases. JAVMA 178: 1163- 1168.
||Lengendre AM: 1998. Blastomycosis. In Green CE (ed) Infectious
Diseases of Dog and Cat, W.B. Saunders Co., Philadelphia, pp
||Ramsey DT:1994. Blastomycosis in a Veterinarian. JAVMA.
|| Rudman DG: 1992. Evaluation of Risk Factors for lastomycosis
in Dogs: 857 cases (1980-1990). JAVMA 201: 1754-1759
||Taboada J: 2000. Systemic Mycoses. In Ettinger SJ (ed). Textbook
of Veterinary Internal medicine, W.B. Saunders Co., Philadelphia.