Overview
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Blastomycosis is a systemic disease caused by a fungus.
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The organism is present in the soil and infection occurs by inhalation of the fungus.
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Once infection is established in the lung, the fungus changes its characteristics by converting from the mycelial form into the yeast form and spreads to other organs causing a disseminated infection.
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This fungus exists in two different forms:
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Hunting dogs that spend a lot of time outdoors and live in endemic areas are at risk for inhaling this organism and developing the disease.
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Some animals may be infected but not show clinical signs for a long time.
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These animals are not a risk for contagion of other animals and people because the stage of the organism present in the animal's tissues is not that of an infectious stage.
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If left untreated, these dogs can become seriously ill.
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Dogs may develop infection in the kidneys, eyes, brain and bones.
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They may have ocular problems or neurological signs like seizures and head tilt.
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In some dogs lameness may be the primary complaint due to infection in the bones.
Symptoms
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Coughing
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Difficulty breathing
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Fever
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Loss of appetite
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Weight loss
Overview
Diagnosis
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Suspicion of blastomycosis comes from the history of living in an area at risk for this infection, especially in animals that hunt or spend a lot of time outside.
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There are some tests that can be run to see if the animal has been exposed to the organism and has produced antibodies against it.
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This type of test (serology) requires a blood sample and is not 100 percent reliable. It could be falsely negative in the early stage of the disease.
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The definitive diagnosis comes from the identification of the fungus in the tissues.
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This is possible when skin lesions are present in the form of nodules that drain purulent material.
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In those cases a biopsy is taken and sent to the laboratory for microscopic examination and for culture.
Treatment
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Affected animals require many months of antifungal therapy.
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Some drugs are given intravenously (amphotericin B) while others are given orally (e.g. ketoconazole).
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Depending on the severity of the disease a combination of drugs may be selected.
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These drugs have the potential to cause kidney and liver damage, thus it is very important that your pet is closely monitored and that blood work is repeated frequently to check for signs of toxicity.
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The prognosis (outcome) depends on the severity of the lung disease, and how extensive is the infection in the body. It is important to take chest radiographs and evaluate the extent of the lung involvement.
Prevention
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It is important that you administer the medications as instructed by your veterinarian and that you monitor the appetite and bowel movements of your pet.
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Some drugs may induce nausea and vomiting. If your pet stops eating, your veterinarian needs to be notified immediately.
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There is no vaccine or effective way of disinfecting the contaminated soil.
Veterinary Care In-depth
Diagnosis In-depth
- Certain diagnostic tests must be performed to confirm the diagnosis of blastomycosis and exclude other diseases that may cause similar symptoms.
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Tests may include:
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A complete medical history and physical examination, including auscultation (listening with a stethoscope) of the lungs, careful examination of the eyes and nervous system, and evaluation of the skin for draining nodules
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A complete blood count (CBC or hemogram) to evaluate the severity and chronicity of inflammation, detect the presence of non-regenerative anemia, and check platelet count.
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The clinical presentation of animals with some diseases associated with low platelet count (Ehrlichiosis, Rocky Mountain spotted fever) can resemble blastomycosis.
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Serum biochemistry tests to determine the effect of blastomycosis on other organ systems, and to evaluate the health of other organ systems, especially the liver and kidneys, before treatment with anti-fungal drugs that can be toxic for the liver and kidneys.
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Rarely, high blood calcium concentration (hypercalcemia) is found in animals with systemic fungal infection and hypercalcemia can occur in diseases that can be confused with systemic fungal infection like lymphosarcoma. Certain blood proteins may be increased in the blood of animals with systemic fungal infection and in those with other chronic infectious diseases.
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Urinalysis to identify urogential involvement, evaluate kidney function and check for bacterial urinary tract infection.
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X-rays of the chest to evaluate the severity of lung involvement and to check for enlarged lymph nodes in the chest.
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Bone involvement also may be identified on X-rays of the chest.
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X-rays of the abdomen to evaluate vital organs, especially the liver and kidneys. Bone involvement also may be identified on X-rays of the abdomen.
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Serologic tests for heartworm disease, brucellosis, and rickettsial infection as well as the agar gel immunodiffusion test to identify blastomycosis.
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The agar gel test is very reliable but may be negative early in the course of infection.
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Finding the blastomyces organism during microscopic examination of material collected from draining skin nodules results in a definitive diagnosis.
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Microscopic examination of a biopsy specimen from affected tissue by a veterinary pathologist can also lead to a definitive diagnosis, but this method is more invasive, and results take longer to return from the laboratory.
Treatment In-depth
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