Diseases / List of Fungal / Algal Diseases / Disease description:

Blastomycosis (with special reference to Bears and Ferrets) 

INFORMATION AVAILABLE

GENERAL INFORMATION

CLINICAL CHARACTERISTICS & PATHOLOGY

INVESTIGATION & DIAGNOSIS

TREATMENT & CONTROL

SUSCEPTIBILITY & TRANSMISSION

ENVIRONMENT & GEOGRAPHY

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General and References

Disease Summary

A fungal infection, usually initially pulmonary, but which can extend throughout the body if untreated. (J14.12.w1)

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Alternative Names (Synonyms)

Blastomyces dermatitidis infection

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Disease Type

Fungal Infection

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Infectious/Non-Infectious Agent associated with the Disease

Blastomyces dermatitidis. Infection is initially respiratory (upper airways not usually affected) with local spread to the bronchial and mediastinal lymph nodes as well as haematogenous spread. In disseminated infection, connective or bony tissues throughout the body may be affected. (J14.12.w1)

Once inhaled, infective conidia are phagocytosed by alveolar macrophages. They are transformed from the mycelial phase to the yeast phase (promoted by body temperature). The yeasts are 8-12 m diameter, thick walled and lacking a capsule. They form daughter cells by budding, with a broad-based attachment. Infection may be localised or disseminated haematogenously or via lymphatics. (J34.33.w1)

Infective "Taxa"

Non-infective agents

--

Physical agents

-- Indirect / Secondary

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References

Disease Author

Debra Bourne MA VetMB PhD MRCVS (V.w5)
Click image for main Reference Section

Major References / Reviews

Code and Title List

J14.12.w1, J34.33.w1
P1.1996.w3

Bears:
B336.51.w51
J2.20.w5
P1.1988.w4, P1.1996.w3

Ferrets:
J4.186.w1, J213.6.w3

Other References

Code and Title List

 

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Clinical Characteristics and Pathology

Detailed Clinical and Pathological Characteristics

General Signs such as cough, anorexia and fever, respiratory distress and weight loss. Other signs vary depending on the organ involved (e.g. uveitis or ophthalmitis with ocular involvement). (J14.12.w1)

Clinical Characteristics

  • General signs: anorexia, depression, lethargy, weight loss, cachexia, fever. (J34.33.w1)
  • Respiratory signs: tachypnoea, dyspnoea, cyanosis, respiratory distress (65 - 85% of affected dogs). (J34.33.w1)
    • Sudden deterioration or death may occur due to pulmonary thromboembolism. (J34.33.w1)
  • Lymph node enlargement (30 - 50% of cases). (J34.33.w1)
  • Ophthalmic: chorioretinitis, anterior uveitis, retinal detachment, secondary glaucoma (20 - 50% of dogs). J34.33.w1
  • Bone: in 10 - 15% of dogs, usually distal to the elbow/stifle. (J34.33.w1)
  • Cutaneous: (30 - 50%) nodules, papules or plaques, variable in size; these may drain exudate which is serosanguineous to purulent.  Sometimes paronychia and occasionally calcinosis cutis. (J34.33.w1)
    • In cats, large dermal abscesses may develop. (J34.33.w1)
  • CNS involvement in less than 5% of dogs, but more common in cats. (J34.33.w1)
  • Respiratory: chronic, dry non-productive cough. (J14.12.w1)
    • Radiography: shadows on the lung fields similar to those seen with pulmonary tuberculosis or carcinoma. (J14.12.w1)
  • Typically lethargy, anorexia, and weight loss, sometimes with subtle respiratory signs  (P1.1996.w3)
  • Skin: fistulae, local lymph node enlargement. (J14.12.w1)
  • Bone: radiographically, bone destruction similar to that with bacterial osteomyelitis. (J14.12.w1)

Clinical pathology does not show any consistent changes:

  • Mild nonregenerative anaemia, mature neutrophilia or neutrophilia with left shift may be rpesent, sometimes hypoalbuminaemia (about 75%), hyperglobulinaemia (50%) or hypercalcaemia (10%). (J34.33.w1)
  • Variably elevated wbc count, increased band cells, monocytosis and slightly elevated serum calcium. (P1.1996.w3)

Radiography

  • Thorax:
    • Abnormalities such as pulmonary infiltration, bullous formation, lung masses, pleural effusion and collapse of lung lobes. (P1.1996.w3)
    • Usually an interstitial pattern (diffuse or nodular), alveolar infiltrate, or hilar lymphadenopathy (70%); less often, fluid or air in the pleural space. (J34.33.w1)
  • Bone (appendicular skeleton): 
    • Osteolysis with periosteal proliferation and associated soft tissue swelling. (J34.33.w1)
BEARS
  • Blastomyces dermatitidis has been reported to cause pneumonia and pleuritis in Ursus maritimus - Polar bear. (B336.51.w51)
  • In one five-year-old male Ursus maritimus - Polar bear, intermittent anorexia, weight loss, and depression/malaise, and intermittent hind leg lameness and weakness. (J2.20.w5, P1.1988.w4)
    • Later, dyspnoea developed and depression worsened. (J2.20.w5)
    • Ophthalmological examination during treatment revealed an inactive hyperpigmented chorioretinal scar in the tapetal region of the left eye. This was compatible with a healed blastomycotic chorioretinal granuloma. (J2.20.w5)
    • Radiography: Pleural effusion; following bilateral thoracocentesis, a miliary nodular interstitial pattern was visible, indicating pulmonary interstitial disease. (J2.20.w5, P1.1988.w4)
    • The haematological and biochemical findings were unremarkable in a five-year-old male Ursus maritimus - Polar bear. (J2.20.w5)
  • Slight monocytosis was noted in one polar bear. (P1.1996.w3)
FERRETS In an 18-month-old female ferret, soon after weaning a litter: (J4.186.w1)
  • Ulcerated, oozing metacarpal pad lesions, also occasional coughing and sneezing, pyrexia (39.5 C, 103.1 F), palpably enlarged spleen and black, tarry faeces. (J4.186.w1)
  • Radiography: 
    • Thoracic: reticulonodular interstitial pneumonia, together with focal consolidation of the middle part of the left lung, plus areas of trapped pleural fluid. 
    • Abdominal: Spleen enlarged. 
    • Findings considered consistent with a mycosis or neoplasia.

    (J4.186.w1)

Incubation

  • Weeks to months. (J34.33.w1)
  • In dogs experimentally, 5 -12 weeks. (J213.6.w3)
BEARS --
FERRETS In an 18-month-old female ferret, soon after weaning a litter, fatal infection. (J4.186.w1)

Mortality / Morbidity

  • About 25 - 30 % mortality. Worse prognosis with severe respiratory involvement or involvement of more than three body systems. (J34.33.w1)
BEARS
FERRETS  

Pathology

--
BEARS
Gross pathology
  • Pneumonia. (B336.51.w51)
  • Pleuritis. (B336.51.w51)
  • On all pleural and peritoneal surfaces of one Ursus maritimus - Polar bear, extensive granulomas were present. (P1.1996.w3)
  • Lung consolidation (nodular to diffuse), due to coalescing granulomas with variable central necrosis or calcification was found in five large carnivores (including one Ursus maritimus - Polar bear). (P1.1996.w3)
  • Note: no pathology was found at necropsy in a polar bear which had been successfully treated for blastomycosis eight years previously. (P1.1996.w3)
FERRETS
Gross pathology

In an 18-month-old female ferret, soon after weaning a litter: (J4.186.w1)

  • Respiratory: Bilateral diffuse granulomatous pneumonia with white to tan miliary nodules throughout the lung parenchyma. Middle portion of the left lung firm, enlarged and tan-yellow in colour. On the costal pleura near the spine, numerous 0.3 - 1.0 cm round, elevated plaques, particularly on the left side.
  • Splenic:  Firm, enlarged spleen.
Histopathology

In an 18-month-old female ferret, soon after weaning a litter: (J4.186.w1)

  • Plumonary: "lobar granulomatous pneumonia with diffuse peribronchial lyphoid hyperplasia", and granulomatous pleurisy. In the middle of the left lobe, severe diffuse fibrosis. In the pleural plaques, large numbers of degenerating Blastomyces dermatitidis plus small numbers of inflammatory cells.
  • Splenic: granulomatous splenitis.
  • CNS: Granulomatous multifocal meningoencephalitis.
  • Culture: from lung and pleural lesions, Blastomyces dermatitidis isolated.

(J4.186.w1)

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Human Health Considerations

  • No proof of transmission from animal to human. (J14.12.w1)
  • Potentially zoonotic; care should be taken when handling infected tissues or caring for individuals with draining wounds. (J34.33.w1)
  • Note: Risk of infection from the organism in culture; culture should be carried out by a professional laboratory. (J213.6.w3)

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Susceptibility / Transmission

General information on Susceptibility / Transmission

Transmission
  • Inhalation of conidiospores and respiratory colonisation. (J14.12.w1, J34.33.w1)
  • Less commonly, penetration (inoculation), leading to localised infection. (J34.33.w1)
  • No proof of animal-to-animal transmission. (J14.12.w1)
Susceptibility
  • Dogs appear to be relatively susceptible (more than other domestic animals). (J14.12.w1, J34.33.w1)
BEARS
Susceptibility
FERRETS One case reported in an 18-month-old female ferret, soon after weaning a litter. (J4.186.w1)

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Disease has been reported in either the wild or in captivity in:

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" volume has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

Host Species List

(List does not contain all other species groups affected by this disease)

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Disease has been specifically reported in Free-ranging populations of:

  • --

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" volume has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

Host Species List

  • --

(List does not contain all other species groups affected by this disease)

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Environment/Geography

General Information on Environmental Factors/Events and Seasonality

  • Fungal growth is encouraged by moist acidic soil contaminated with decaying vegetation or animal faeces. (J34.33.w1)
  • Environmental moisture is thought to be important for spore dissemination. (J34.33.w1)

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Regions / Countries where the Infectious Agent or Disease has been recorded

  • This organism is found in the Americas, from Canada southwards to Central America. (J14.12.w1)
  • Prevalence is greatest in the Mississippi, Missouri and Ohio river valleys (J34.33.w1, J213.6.w3), also in the mid-Atlantic and southern states as well as southern Canadian waterways. (J34.33.w1)

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Regions / Countries where the Infectious Agent or Disease has been recorded in Free-ranging populations

  • --

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General Investigation / Diagnosis

General Information on Investigation / Diagnosis

  • Organisms may be identified on cytology or histopathological examination. (J34.33.w1, J213.6.w3) This is considered definitive.
    • Budding organisms may or may not be found on cytological examination of the respiratory tract (found in one of four large carnivores in one study). (P1.1996.w3)
    • Identification of organisms from lymph node aspirate or aspirate/exudate from dermal lesions. ( J34.33.w1) Note: lung aspirates, tracheal wash or alveolar lavage will only reveal organisms about 50% of the time. (J34.33.w1)
  • Thoracic abnormalities seen on radiography in affected large carnivores, including an Ursus maritimus - Polar bear, have included pulmonary iniltrates, bullous formation, lung lobe collapse, lung masses and pleural effusions. (P1.1996.w3)
  • Histopathological findings: in the lungs, typically granulomatous lesions containing neutrophils, lymphocytes and monocytes. (J14.12.w1) 
    • Bower stain easily reveals Blastomyces dermatitidis. (J14.12.w1)
  • From pus or biopsy specimens. (J14.12.w1) e.g. from the respiratory tract (P1.1996.w3).
    • Wet mount with potassium hydroxide to reveal thick-walled yeast cells, 8 - 15 um, having buds with a broad area of attachment.
    • Culture of both the tissue phase and the mycelial phase. (J14.12.w1)
      • Incubation on blood agar plates at 37 C for the tissue phase. (J14.12.w1)
      • Incubation on Sabouraud agar at 22 C for the mycelial phase. (J14.12.w1)
      • Note: growth may require several weeks. (J34.33.w1)
    • Grown from two of four large carnivores in one study. (P1.1996.w3)
  • Serology: 
    • Agar gel immunodiffusion (AGID) test. (J2.34.w5, J34.33.w1)
      • This is against the A-antigen of the fungus. Sensitivity is 60-90%, specificity up to 96%. May be negative early in the disease. May become negative or remain positive if the infection is treated. (J34.33.w1)
      • Sensitivity greater than 90% in dogs. (J213.6.w3)
      • Not very useful in cats. (J34.33.w1)
      • In a survey of large carnivores, agar gel immunodiffusion (AGID) titres were positive in two of three carnivores at initial testing, and equivocal in the third, but positive a month later. One animal was positive when the CSF was tested. (P1.1996.w3)
      • In six cases in nondomestic felids, AGID was positive in three of the four individuals diagnosed antemortem. (J2.34.w5)
    • A radioimmunoassay has been developed which tests for W1-1 antigen, but this is not commercially available. Specificity of 100% and sensitivity of 90% reported, sometimes remaining positive with successful treatment. (J34.33.w1)
BEARS
  • In one five-year-old male Ursus maritimus - Polar bear. (J2.20.w5, P1.1988.w4)
    • Cytological examination and culture of serosanguinous fluid obtained by bilateral thoracocentesis. Microscopic examination of a wet mount following centrifugation of 5 mL of the fluid revealed three yeast cells consistent with Blastomyces sp.; initial cultures were negative but culture of a pellet from centrifugation of the pleural fluid grew Blastomyces dermatitidis. (J2.20.w5, P1.1988.w4)
    • Initially suspicious results from agar gel diffusion, but not positive; a stronger reaction was obtained later (J2.20.w5, P1.1988.w4)
FERRETS In an 18-month-old female ferret, soon after weaning a litter: (J4.186.w1)
  • Radiographic findings were consistent with mycosis (or neoplasia).
  • Tissue imprint from the ulcerated pad showed broad-based budding yeasts, consistent with Blastomyces dermatitidis.
  • Agarose gel immunodiffusion test positive for antibodies to Blastomyces dermatitidis.
  • Further confirmation by culture of Blastomyces dermatitidis from the lungs and pleural leisons after necropsy.

    (J4.186.w1)

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Similar Diseases (Differential Diagnosis)

Primary osteosarcoma produces radiographically similar lesions of the appendicular skeleton. (J34.33.w1)
FERRETS
  • Radiographic findings were also consistent with neoplasia. (J4.186.w1)

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Treatment and Control

Specific Medical Treatment

  • Treatment is required if the infected individual shows clinical disease (i.e. they have not cleared the infection spontaneously). (J34.33.w1)
  • Antifungal treatment allows survival of about 70-75% of treated dog; those with severe respiratory infection, multisystemic infection or CNS involvement are less likely to survive. (J34.33.w1)
  • Itraconazole. (B336.51.w51)
    • This is the treatment of choice. (J34.33.w1)
    • In dogs, 5 mg/kg orally every 12 hours for 60 to 90 days (or for one month after resolution). (J34.33.w1)
    • In cats, 5 mg/kg orally every 12 hours for five days then daily for 60 to 90 days (or for one month after resolution). (J34.33.w1)
    • Oral itraconazole at 2 mg/kg twice daily or 5 mg/kg daily produces high drug concentrations in serum, pleural effusion fluid and CSF. (P1.1996.w3)
  • Amphotericin B is effective (similar to itraconazole) but must be given parenterally and involves a risk of nephrotoxicity. (J34.33.w1)
    • The lipid-complexed formulation involves less risk of nephrotoxicity. (J34.33.w1)
    • In dogs, 0.5 mg/kg intravenously three times a week to a cumulative dose of 4 - 6 mg/kg. (J34.33.w1)
    • In dogs, Liposomal amphotericin B, 1 mg/kg intravenously three times a week, cumulative dose 12 mg/kg. (J34.33.w1)
    • In cats, 0.25 mg/kg intravenously three times a week to a cumulative dose of 4 mg/kg. (J34.33.w1)
  • Ketoconazole is less effective. (J34.33.w1)
    • In dogs, 5 -15 mg.kg orally every 12 hours fr at least three months. Give concurrently with amphotericin B initially. (J34.33.w1)
    • In cats, 10 mg/kg every 12 hours for at least 90 days. Give concurrently with amphotericin B initially. (J34.33.w1)
  • Itraconazole
    • 5 mg/kg orally every 12 hours for five days then daily for 60 to 90 days (or for one month after resolution). (J34.33.w1)
    • 5 mg/kg orally every 12 hours. (J213.6.w3)
  • Fluconazole 5 mg/kg orally every 12 hours for at least 60 days (or for one month after resolution). (J34.33.w1)
  • NOTE: Antifungal treatment (itraconazole or amphotericin B) should be given for at least 60 days and at least 30 days beyond resolution of clinical signs and radiographical lesions; at least 90 days of treatment for individuals with severe lung disease. (J34.33.w1)
    • Dogs treated for 60-90 days have a recurrence rate of about 20%. (J34.33.w1)
  • Note: Individuals dying after the start of treatment usually die within the first five days, probably due to the death of the organism in the body, and the associated inflammatory response. (J34.33.w1)
BEARS
  • Oral Itraconazole, 4.3 mg/kg daily, divided into two doses, produced a "return to clinical normalcy after 90 days" in a Ursus maritimus - Polar bear. (P1.1988.w4)
  • Oral itraconazole at 2 mg/kg twice daily produced clinical improvement within one week. No adverse effects were seen with 90 days of treatment. (P1.1996.w3)
  • Itraconazole, 4.3 mg/kg daily, divided into two doses and continued for 90 days in a five-year-old male Ursus maritimus - Polar bear. (J2.20.w5)
    • For the first 10 days, amoxycillin was given also, 22 mg/kg orally twice daily to help prevent the development of secondary bacterial pneumonia. (J2.20.w5)
    • The thorax was drained by bilateral tube thoracostomy to relieve the dyspnoea. (J2.20.w5)
    • Therapeutic concentrations were reached and passed within three hours of the bear receiving its first oral dose of itraconazole. (J2.20.w5)
    • There was apparent clinical improvement by one week after the start of treatment and the bear continued to be clinically normal one year after diagnosis. (J2.20.w5)
FERRETS In an 18-month-old female ferret, soon after weaning a litter: (J4.186.w1)
  • Oral Ketoconazole 5 mg once daily for 60 days plus 0.8 mg/kg Amphotericin B (0.5 mg in 1 mL 5% dextrose) intravenously every second day. (J4.186.w1)
    • Monitoring blood urea nitrogen (BUN). (J4.186.w1)
    • Actual treatment: the ferret developed anorexia, pyrexia and azotaemia when amphotericin B was given, therefore the dose was halved (0.4 mg/kg, total 0.25 mg per treatment) and given at intervals of about a week. (J4.186.w1)
    • Treatment was initially effective, with resolution of the metacarpal pad lesion, and reduction in the size of the consolidated area of the lung. (J4.186.w1)
    • However, after five treatments with amphotericin B, inflammation of veins made further intravenous injections impossible. Therapy changed to the same dose of amphotericin B subcutaneously every two days, with ketoconazole continuing as before.
    • The ferret relapsed after two weeks and was euthanased. (J4.186.w1)
  • Suggestions for future cases:
    • Either install a semi-permanent catheter into a jugular vein for intravenous amphotericin B treatment, or give this drug by intraperitoneal injection. OR consider increasing the ketoconazole to 30 mg/kg daily. (J4.186.w1)
    • Itraconazole, 5 mg/kg orally every 12 hours. (J213.6.w3)
Related Techniques

 

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General Nursing and Surgical Techniques

Supportive care:
  • Oxygen therapy if the animal is hypoxaemic. (J34.33.w1)
  • Bronchodilators. (J34.33.w1)
  • Analgesics for individuals with pain due to bony lesions. (J34.33.w1)
  • If secondary bacterial infection is suspected, antibiotics may be used. (J34.33.w1)
  • Keep dermal lesions shaved, clean and dry. (J34.33.w1)
BEARS --
FERRETS
  • Supportive: when the ferret was anorectic or dehydrated, subcutaneous lactated Ringer's solution and 5% dextrose solution. (J4.186.w1)
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Preventative Measures

Vaccination --
FERRETS --
Prophylactic Treatment

--

FERRETS --
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Environmental and Population Control Measures

General Environment Changes, Cleaning and Disinfection --

FERRETS

  • --
Population Control Measures --
FERRETS --
Isolation, Quarantine and Screening --
FERRETS --
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