Blastomycosis

Posted on June 12, 2015

Blastomycosis is a disease caused by tiny spores of a fungus, Blastomyces dermatitidis commonly living in soil.  Inhalation of the spores infects the lungs, initially producing fungal pneumonia.  It can spread throughout the body, commonly infecting eyes, bones, skin, and lymph nodes.   Twenty-five percent of dogs will die despite treatment, while twenty-five percent that respond well will relapse over the next year, requiring a second course of treatment with a ninety percent cure rate.  Mortality rate is high in dogs with respiratory difficulty and severe disease.  Dogs that recover are probably immune and reinfection is unlikely.

Symptoms of blastomycosis

1.       Infection in the lung can cause increased respiratory effort, coughing, exercise intolerance, fever, loss of appetite and weight loss.  Lung inflammation can get worse after treatment begins because of the release of products from dead organisms.

2.       Bone involvement often cause lameness.

3.       Skin involvement results in ulcerated lesions and draining abscesses.

4.       Eye involvement result in red, painful eyes with discharge.

Testing for blastomycosis

1.       A Microscopic examination performed from skin lesions or lymph nodes

2.       Chest radiographs to identify lung changes characteristic of blastomycosis.  It may resemble bacterial pneumonia making difficult a definitive diagnosis.

3.       Finding antibodies against blastomyces in a dog’s serum strongly suggests infection.  Some early infections may not have developed antibodies.

4.       Probable diagnosis should be made by considering the symptoms, laboratory finding and previous treatments.

5.       Fungal infections that do not improve with antibiotic treatments are suggestive of blastomycosis.

Treatment of blastomycosis

1.        Usually treated with an oral antifungal drug called itraconazole.

2.       Those that can take oral medication or with brain disease are treated intravenously with amphotericin B.

3.       A two to three month treatment plan may be necessary to eliminate Blastomyces depending on disease severity.

4.       Dogs on itraconazole need to be monitored for liver toxicity, and dogs on amphotericin B for kidney damage.

5.       After treatment, diseased tissue examined for reoccurrence.   Chest or bone radiographs may be retaken depending on infection.

6.       Currently, no commercial vaccination against blastomycosis is available.

Blastomyces fungi facts

1.       Dogs are infected that live near wet areas where blastomyces grow best.

A.      Rivers

B.      Lakes

C.      Swamps

D.      Streams

E.       Ponds

2.       Blastomyces requires acidic soil to grow.

3.       Most cases occur near Tennessee, Mississippi, and Ohio Rivers, and The Great Lakes.

4.       People can become infected with blastomyces, however dogs are 10 times more likely to become infected.   Dogs are not infectious to their owners, except in rare dog bite cases.  It is important to tell your physician if a pet is infected with blastomycosis, especially when suffering a respiratory infection or skin disease.  The disease is usually evident in dogs before humans.

5.       Larger dogs become infected more often than smaller dogs

6.       Cats rarely suffer blastomycosis.

7.       There is no practical way to eradicate blastomyces from the environment.

8.       Susceptible dogs should have restricted access to sites of water.