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Histoplasmosis

This fungal infection has several other names, including Ohio Valley disease, Central Mississippi Valley disease, Appalachian Mountain disease, and Darling's disease. In the United States, histoplasmosis occurs in three forms: primary acute histoplasmosis, progressive disseminated histoplasmosis (acute disseminated or chronic disseminated disease), and chronic pulmonary (cavitary) histoplasmosis. The last form produces cavitations in the lung similar to those seen in pulmonary tuberculosis.

A fourth form, African histoplasmosis, occurs only in Africa and is caused by the fungus Histoplasma capsulatum var duboisii.

Histoplasmosis occurs worldwide, especially in the temperate areas of Asia, Africa, Europe, and North and South America. In the United States, it's most prevalent in the southeastern, mid-Atlantic, and central states.

The incubation period ranges from 5 to 18 days, although chronic pulmonary histoplasmosis may progress slowly for many years. The prognosis varies with each form. In a small number of patients, histoplasmosis becomes progressive and potentially fatal. Chronic pulmonary infections occur more often in males over age 40, particularly those with a history of cigarette smoking. An acute and rapidly fatal course is more likely to occur in young children and immunosuppressed patients, such as persons with acquired immunodeficiency syndrome.

Causes

Histoplasma capsulatum (histo) spores spread from the lungs to the eye, lodging in the choroid, a layer of blood vessels that provides blood and nutrients to the retina. The retina is the light-sensitive layer of tissue that lines the back of the eye. Scientists have not yet been able to detect any trace of the his to fungus in the eyes of patients with ocular histoplasmosis syndrome. Never the less, there is good reason to suspect the his to organism as the cause of OHS.

Symptoms and Signs

Signs and symptoms that occur in rare cases include the following:

  • Acute, flu-like infection – includes fever, chills, cough, chest pain, and headache 
  • Chronic lung infection – develops gradually over weeks to months and produces a progressive, worsening cough, weight loss, night sweats, and possibly, shortness of breath 

Diagnostic tests

Culture is the preferred method of diagnosis but is difficult. Blood cultures should be done by lysiscentrifugation technique. In disseminated forms, culture of bone marrow, mucosal lesions, liver, and bronchiolar lavage are helpful. Sputum cultures are preferred in chronic pulmonary histoplasmosis but may take 2 to 4 weeks to culture. A radioactive assay for histoplasma antigen in blood or urine is commercially available and useful in diagnosis.

Treatment

Treatment includes antifungal therapy, surgery, and supportive care.

Antifungal therapy plays the most important role. Except for asymptomatic primary acute histoplasmosis (which resolves spontaneously) and the African form, histoplasmosis requires high-dose or long-term (10­week) therapy with amphotericin B or ketoconazole.

Surgery includes lung resection to remove pulmonary nodules, a shunt for increased intracranial pressure, and cardiac repair for constrictive pericarditis.

Supportive care includes oxygen for respiratory distress, glucocorticoids for adrenal insufficiency, and parenteral fluids for dysphagia caused by oral or laryngeal ulcerations. Histoplasmosis doesn't necessitate isolation.

Prevention
  • It is not practical to test or decontaminate all areas that are known to be or might be contaminated with the histoplasmosis fungus, but these steps can reduce the risk of exposure:
  • Avoid areas where the fungus might be growing, especially areas with accumulations of bird or bat droppings. The fungus often grows around old chicken houses, in caves and other areas where bats live, and around starling and blackbird roosts.
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