Case Presentation

A 25-year-old previously healthy man was admitted to a Colorado hospital with a 12-day history of fever, weight loss, fatigue, joint pain, and productive cough. His private physician had treated him with two antibiotics over the prior 8 days, but there was no response to the treatment.

Seven and 14 days before his symptoms began, the man was employed in a prairie dog relocation project, digging up and destroying the abandoned burrows.The work required using a gasoline-powered device that created clouds of dust, and also using hand trowels, which brought his face close to the soil. Above average rainfall had occurred in the 2 weeks before the work was done.

A few days after the man was admitted, a coworker entered the hospital with similar symptoms.

Initial laboratory studies including examination of the man's sputum were not helpful in making the diagnosis. A CT scan (an X-ray procedure) was then performed and revealed multiple small dense shadows throughout both lungs.

1. What are the diagnostic considerations in this individual?

2. How is the diagnosis to be made?

3. What is the natural history of the causative organism?

4. Could the disease have been prevented? Is treatment indicated?

Discussion

1. The CT scan, showing multiple shadows in both lungs, could not distinguish between various possible causes, including certain cancers, allergic lung diseases, tuberculosis, and fungal diseases.The acute nature of the illness, and the fact that his coworker contracted a similar illness at almost the same time, suggested an infectious cause. Exposure to dust arising from the soil 14 and 7 days before symptoms began pointed to a soil organism, and the lack of response to antibiotic therapy suggested that it might be fungal. Colorado, however, is not in the geographical areas where histoplasmosis, coccidioidomycosis, or other fungal lung diseases generally occur.

2. A lung biopsy was performed.The man was anaesthetized, an incision made in the chest to expose the lung, an area of abnormality identified, and a small portion excised for microscopic studies and culture. Microscopic examination revealed cells of a large spherical fungus, reproducing by a single bud, typical of Blastomyces dermatitidis, confirmed 10 days later when colonies of the organism first appeared in culture and were identified by a nucleic acid probe.These findings established the diagnosis of blastomycosis.

3. Blastomyces dermatitidis is a dimorphic soil fungus occurring mainly in the Mississippi and Ohio River valleys, and in the southeastern states, thus largely overlapping the distribution of Histoplasma capsulatum. Even in these areas it uncommonly causes human disease, and it rarely does so in Colorado. In the present case, recent heavy rainfall and soil heavily enriched with feces and other material from the animal burrows provided conditions likely to enhance growth of the fungus.The conditions under which the people worked allowed for possible inhalation of large numbers of B. dermatitidis spores.

4. Blastomycosis is probably preventable by using face masks that reliably exclude dust, and other dust control measures when working with potentially contaminated soil. Individuals with less extensive lung infection than this man may heal their disease without treatment, but the disease is prone to spread via the bloodstream to the skin, where it causes large disfiguring chronic ulcers, and less commonly to bones and other body tissues. In this instance, both men were treated for 10 days with intravenous amphotericin B, followed by 6 weeks of itraconazole.

Source: Centers for Disease Control and Prevention. 1999. Morbidity and Mortality Weekly Report 48: 98.

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