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Respiratory System Diseases

Fungal Respiratory Diseases

Several fungal species will opportunistically cause secondary infections or infect the respiratory system of patients with compromised immune systems.

Aspergillus fumigatus is a fungus found everywhere, and spores of this species are inhaled by most people daily. A. fumigatus may cause an invasive infection in the lungs in people with immunodeficiency or those already suffering from other respiratory infections. The fungus will grow as a mold in the lungs and form balls of fungal tissue. The growth may cause no symptoms or may result in hemorrhage, severe bleeding, and death. Diagnosis is through imaging, X-ray or computed tomography, of the chest. Treatment involves antifungal therapy and surgical removal of infected lung tissue.

Fungi are also able to cause pneumonia, though infection is much less common. The fungus Candida albicans, which is part of the normal microflora in the oral cavity, can cause pulmonary candidiasis when it infects the lungs. The symptoms of C. albicans pulmonary infection include cough, fever, chest pain, and trouble breathing, and it can develop into pneumonia. Pneumocystis jiroveci and Cryptococcus neoformans are more common fungal causes of pneumonia and are generally associated with immune suppression, such as in those under treatment after transplant surgery or patients with HIV.

The fungus Histoplasma capsulatum is found in soils and is associated with the feces of bats or birds. Particles of soil can become aerosolized when the soil is disrupted, and spores of the fungus are then inhaled. H. capsulatum causes histoplasmosis, which presents with flu-like symptoms and if untreated, or in immunocompromised patients, occasionally leads to a chronic and more severe infection. Histoplasmosis may also result in mediastinitis, inflammation of the tissue in the mid-chest. Diagnosis is by identification of the fungus from mucus or blood samples or by immunoassay to detect antigens in blood or urine. Treatment with amphotericin B and itraconazole antifungals is recommended for severe or chronic infections.

Coccidioidomycosis, also known as valley fever, is caused by Coccidioides immitis or Coccidioides posadasii, which are endemic to the southwestern United States and neighboring Mexico, where they live in the soil and can be inhaled when soil is airborne. Symptoms of valley fever are bronchitis and pneumonia with fatigue, cough, fever, shortness of breath, headache, night sweats, and rashes. Diagnosis can be made based on symptoms and chest imaging, though definitive identification requires immunoassays to detect fungal antigens or PCR to amplify fungal genes. Mild acute cases will clear without treatment. More severe cases have been treated with an assortment of antifungal therapies.

Cryptococcosis is a potentially fatal fungal disease that often opportunistically infects patients with AIDS and other immunosuppressive illnesses. Spores of Cryptococcus neoformans or Cryptococcus gattii are inhaled from unknown sources. Fever, fatigue, confusion, and pulmonary infection may result. The infection can also spread to the central nervous system to cause meningitis, and therefore patients diagnosed with pulmonary cryptococcosis are encouraged to receive a spinal tap. Treatment involves antifungal therapy.