Histoplasma capsulatum is a fungus found in the soil of the central and eastern United States (especially Mississippi and Ohio river valleys), eastern Canada, Mexico, Central America, and South America.

The infection occurs when a person breathes in the reproducing parts of the fungus, called spores. Those who have a healthy immune system usually do not have symptoms, or only mild ones.

This "acute" infection does not last, but can leave a person with small scars (granulomas). These scars are sometimes difficult to distinguish from growths in the lung.

However, the infection can cause severe illness right away, or redevelop years after the first exposure, if a person's immune system is weakened by:

• Cancer
• Chemotherapy
• Immune-suppressing drugs
• HIV infection

Risk factors for chronic pulmonary histoplasmosis include:

• Living in or traveling to central or eastern United States
• Exposure to soil or particles contaminated with droppings of chickens, bats, or blackbirds
• Pre-existing COPD
• Weakened immune system, such as in people who have AIDS

• Chills
• Cough that brings up mucus or pus
• Fever
• Joint stiffness
• Shortness of breath
• Skin involvement (erythema nodosum )
• Unintentional weight loss

Tests that may be used to diagnose chronic pulmonary histoplasmosis include:

• Biopsy of infected tissue, such as open lung biopsy or bone marrow biopsy
• Bronchoscopy with transbronchial biopsy or bronchoalveolar lavage
• CBC
• Chest CT scan
• Chest x-ray
• Histoplasma complement fixation titer
• Histoplasma urinary antigen test
• Immunodiffusion test
• Sputum culture and stain

The doctor will prescribe antifungal medications to control the infection within the lung.

The infection usually goes away with antifungal medication, but scarring inside the lung often remains. Histoplasmosis is unusual enough that if you develop it, your health care provider should check to find out whether another disease is weakening your immune system.

Often, those who have had chronic pulmonary histoplasmosis must follow up with their doctor, who will check for signs of relapse.

In rare cases, a pulmonary histoplasmosis infection can spread through the blood to other organs. This is called disseminated histoplasmosis . People who have a suppressed immune system and very young children are more likely to develop this condition. If this occurs, the prognosis is less favorable.

• Arthritis
• Disseminated histoplasmosis
• Lung scarring (fibrosis)
• Pericarditis
• Respiratory insufficiency

Call for an appointment with your health care provider if you develop symptoms of chronic pulmonary histoplasmosis.

Call your health care provider if your symptoms continue despite treatment, or if you have breathing difficulty or symptoms of disseminated histoplasmosis.

Be aware of your surroundings, especially if you are in a weakened state from another medical condition, or from immune-suppressing medications.