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 from produces cavitations in the lung similar to those seen in pulmonary tuberculosis.

A fourth form, African histoplasmosis, occurs only in African 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, history plasmosis 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

Histoplasmosis is caused by H.capsulatum, which is found in the stool of birds and bats and in soil contaminated by their stool, such as that near roosts, chicken coops, barns, caves, and underneath bridges.

Transmission occurs through inhalation of H. capsulatumor H. capsulatum var.duboisii spores or through the invasion of spores after minor skin trauma.

Signs and symptoms

Many otherwise healthy people show no symptoms of infection at all. When symptoms do occur, they appear 3-17 days after exposure (average time is 10 days). The symptoms are usually mild and resemble those of a cold or flu; fever , dry cough , enlarged lymph glands, tiredness, and a general feeling of ill health. A small number of people develop bronchopneumonia. About 95% of people who are infected either experience no symptoms or have symptoms that clear up spontaneously. These people then have partial immunity to re-infection.

Diagnostic tests

The diagnosis of histoplasmosis depends on the underlying condition. Tests may include analysis of the organism in sputum, lung tissue, blood, cerebrospinal fluid (CSF), or bone marrow tissue, as well as antigen tests performed on blood, urine, or CSF.

In addition, certain pathologic findings may be seen in tissue which may support the diagnosis of histoplasmosis.

Treatment

Treatment includes anti-fungal 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

Prevention of histoplasmosis relies on avoiding exposure to dust in a contaminated environment. Before anyone cleans chicken coops or other contaminated soil, spraying with water is advisable to reduce dust.

Persons working in contaminated areas should use protective clothing such as gloves and coveralls. They should also use a respirator equipped with a high efficiency particulate air (HEPA) filter that is capable of filtering particles down to two microns in size. For major clean up operations of prolonged exposure, a powered air purifying or supplied air respirator may be necessary.