Blastomycosis is a rare infectious multisystem disease that is caused by the fungus Blastomyces dermatitidis. The symptoms vary greatly according to the affected organ system. It is characterized by fever, chills, cough, and/or difficulty breathing (dyspnea). In the chronic phase of the disease, the lungs and skin are most frequently affected. The genitourinary tract and bones may also be involved.
Symptoms
Blastomycosis is an infectious disease characterized by fever, chills, headaches, chest pain, weight loss, night sweats, cough, and/or difficulty breathing (dyspnea). Some affected individuals do not experience these symptoms although they are actively infected (asymptomatic). Muscle and joint pain may occur during the acute stage which typically lasts less than three weeks. The disease may resolve on its own or persist into the chronic form of the infection. Chronic Blastomycosis, which lasts more than three weeks, may affect the lungs, skin, bones, joints, genitourinary tract, and/or central nervous system.
Involvement of the skin is very common in individuals with Blastomycosis. Wart-like (verrucous) and small raised pus-filled (papulopustular) lesions are common. They may be violet-colored and have very small abscesses around the borders of the lesions. Nodular lesions may be present under the skin (subcutaneous) and are usually accompanied by an active fungal infection of the lungs.
When Blastomycosis affects the lungs, which are common sites of fungal involvement, it usually takes the form of chronic pneumonia. Symptoms may include a cough accompanied by thick sputum, chest pain, difficulty breathing, and/or rapid heartbeat. In some severe cases of Blastomycosis, Respiratory Distress Syndrome may develop, characterized by excessive deep and rapid breathing (hyperventilation) and insufficient levels of oxygen in the circulating blood (hypoxemia). Affected individuals typically require mechanical ventilation to assist in breathing. (For more information on this disorder, choose “Respiratory Distress” as your search term in the Rare Disease Database.)
Blastomycosis may also affect the bones and cause lesions that destroy bone tissue (osteolytic). The ribs, vertebrae of the spine, and the long bones of the arms and legs are most frequently involved. In many cases, these lesions are painless but may develop an overlying abscess.
Involvement of the urogenital tract is common in males with Blastomycosis. In about 30 percent of cases, the prostate gland and the tubes that carry sperm from the testes (epididymis) are infected by the fungus. Symptoms may include inflammation, swelling, and/or pain in the groin. Involvement of the central nervous system, liver, spleen, gastrointestinal tract, thyroid, adrenal glands, and other organs has also been reported in chronic cases of Blastomycosis.
Causes
Blastomycosis is a rare infectious disease caused by the fungus Blastomyces dermatitidis. This fungus grows and is inhaled through mold spores. In the body, the fungus converts to yeasts and invades the lungs. It travels throughout the body through the blood. Blastomycosis usually affects people with a compromised immune system.
Affected Populations
Blastomycosis affects males and females in equal numbers. The organism that causes this disease (Blastomyces dermatitidis) is most common (endemic) in the south-central and southeastern portions of the United States. It may also be found around the perimeter of the Great Lakes, and along the St. Lawrence River in Canada. Blastomycosis has also been reported in Mexico, the Middle East, Africa, India, and South and Central America.
The natural habitat of this fungus is unclear but it is suspected to come from the soil. Farmers, construction workers, and others who work with soil appear to be at increased risk for Blastomycosis. Also at increased risk for severe chronic Blastomycosis are individuals who have a compromised immune system such as people with Acquired Immunodeficiency Syndrome (AIDS), these taking medications that suppress the immune system, and the elderly.
Diagnosis
The diagnosis of Blastomycosis is confirmed by clinical evaluation that includes chest X-ray studies which may reveal findings that are consistent with fungal pneumonia (i.e., consolidation or cavitation). The direct microscopic examination of infected material (i.e., pus, sputum, or urine) is also performed. The tissue samples are prepared with potassium hydroxide which makes the yeast cells easily visible. Growing tissue samples and then isolating Blastomyces dermatitidis from the culture also confirms the diagnosis of Blastomycosis. Skin testing and blood tests are not helpful in the diagnosing Blastomycosis.
Pulmonary Blastomycosis may be mistaken for malignancy such as lung cancer. Examination of the throat with a special instrument (bronchoscopy) may be required to confirm the diagnosis of Blastomycosis. Cutaneous Blastomycosis of the skin may also resemble certain forms of skin cancer.
Treatment
The treatment of choice for both acute and chronic forms of Blastomycosis, especially those involving the central nervous system, is the oral administration of the antibiotic drug amphotericin B. If the disease is mild to moderate, then ketoconazole may be the drug of choice. Prolonged therapy may be necessary in some cases and relapses may occur. When the central nervous system is involved, the drug amphotericin B is usually administered. Affected individuals who cannot tolerate amphotericin B may be treated with hydroxystilbamidine isethionate. This drug is difficult to administer and may have various side effects. Another treatment is symptomatic and supportive. Other newer antifungal drugs such as fluconazole and itraconazole appear to be effective for the treatment of mild or moderate cases.
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