Several tpes of histoplasmosis exist, ranging from mild to life-threatening. The most benign form produces no signs or symptoms, but severe infections can cause serious problems throughout your body as well as in your lungs. When signs and symptoms do occur, they usually appear three to 17 days after exposure.

Mild to moderate cases

Asymptomatic primary histoplasmosis. This is the most common form of histoplasmosis and usually causes no signs or symptoms in otherwise healthy people who become infected. The only sign of infection may be small scars in the lungs. In that case, special radiologic testing can usually confirm that nodules aren't cancerous.

Acute symptomatic pulmonary histoplasmosis. This form of histoplasmosis tends to occur in otherwise healthy people who have had intense exposure to H. capsulatum. Because the severity of the disease depends on the number of fungus spores inhaled, reactions may range from a brief period of not feeling well to serious illness. Typical signs and symptoms include:

• Fever
• Headache
• Dry cough
• Chills
• Chest pain
• Weight loss
• Sweats

In some cases, arthritis or pericarditis — an inflammation of the sac that surrounds the heart — may develop weeks or months after the initial infection. These problems aren't a sign that the infection has spread outside your lungs. Instead, they develop because your immune system responds to the fungus with an unusual amount of inflammation.

On the other end of the spectrum, people who have inhaled a large number of spores may develop severe acute pulmonary syndrome, a potentially life-threatening condition in which breathing becomes difficult. Acute pulmonary syndrome is frequently referred to as spelunker's lung because it often occurs after intense exposure to bat excrement stirred up by explorers in caves.

Moderate to severe

Chronic pulmonary histoplasmosis. This type of histoplasmosis usually affects people with an underlying lung disease such as emphysema. It's most common in white, middle-aged men. The disease is chronic and if left untreated may progress to disabling lung problems. Signs and symptoms include:

• Fatigue
• Fever
• Night sweats
• A cough that may bring up blood

Disseminated histoplasmosis. Occurring primarily in infants and people with compromised immune systems, disseminated histoplasmosis can affect nearly any part of the body, including your eyes, liver, bone marrow, skin, adrenal glands and intestinal tract. Untreated disseminated histoplasmosis is usually fatal. Depending on which organs are affected, people with this form of the disease may develop:

• Anemia
• Pneumonia
• Pericarditis
• Meningitis
• Adrenal insufficiency
• Ulcers of the mouth, tongue or intestinal tract

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Histoplasma capsulatum is primarily found in the temperate regions of the world and is the most common fungus in the United States. It's endemic in the Ohio, Missouri and Mississippi river valleys, where the great majority of people have been exposed.

The fungus thrives in damp soil that's rich in organic material, especially the droppings from birds and bats. For that reason, it's particularly common in chicken and pigeon coops, old barns, caves and parks.

Birds themselves aren't infected with histoplasmosis — their body temperature is too high — but they can carry H. capsulatum on their feathers, and their droppings support the growth of the fungus. Birds commonly kept as pets, such as canaries and parakeets, aren't affected. And although bats, which have a lower body temperature, can be infected, you can't get histoplasmosis from a bat or from another person.

Instead, you develop histoplasmosis when you inhale the reproductive cells (spores) of the fungus. The spores are extremely light and float into the air when dirt or other contaminated material is disturbed. That's why a high number of cases occur in farmers, landscapers, construction workers, spelunkers and people living near construction sites.

Histoplasmosis and your lungs
Because the spores of H. capsulatum are microscopic in size, they can easily enter your lungs and settle in the small air sacs. There, the spores are trapped by macrophages — immune system cells that attack foreign organisms. The macrophages carry the spores to lymph nodes in your chest, where they continue to multiply. This may lead to inflammation, scarring and calcium deposits. In cases of heavy infection, the lymph nodes may become so enlarged that they obstruct your esophagus or your lungs' airways.

Most often, however, you're not likely to have noticeable signs and symptoms, and the infection clears on its own without treatment. But if your immune system isn't able to eliminate the spores, they can enter your bloodstream and travel to other parts of your body. In that case, you may develop a variety of severe problems that can be fatal if not diagnosed and treated quickly.

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Anyone exposed to H. capsulatum is likely to become infected. People who inhale a huge number of spores — those who work with heavily infected soil or have close contact with bats, for example — are more likely to develop signs and symptoms.

Most at risk of infection

• Farmers
• Poultry keepers, especially when cleaning chicken coops, pigeon roosts, and bat-infested barns or lofts
• Construction workers, especially those who work around old buildings with roosting birds
• Landscapers and gardeners
• People involved in building roads
• People who monitor bird populations or who have contact with bats or bat caves
• Archeologists
• Geologists

Most at risk of severe infection
Because their immune systems are weakened, the following people are most likely to develop disseminated histoplasmosis, the more serious form of the disease:

• Infants and very young children.
• Older adults. The risk of disseminated histoplasmosis increases with age.
• HIV-positive people or those with AIDS.
• People receiving chemotherapy or long-term treatment with corticosteroid drugs such as prednisone.
• People who have had organ transplants and are taking anti-rejection medications.

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Contact your doctor if you live in an area where histoplasmosis is common and you develop chest pain, cough and a fever. Although many illnesses cause similar signs and symptoms, your doctor may want to test you for the presence of H. capsulatum. If your immune system has been weakened by illness or medications, seek medical care immediately.

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Histoplasmosis can cause a variety of signs and symptoms, many of which resemble those of other illnesses. For that reason, it can be particularly challenging to diagnose. Complicating the matter further is the large number of tests available for detecting the presence of the fungus — each of which has some limitations. These tests include:

• Fungal culture. This is considered the gold standard for confirming a diagnosis of histoplasmosis. During the test, a small amount of blood, sputum or tissue from your lymph nodes, lung or bone marrow is placed on a medium that enhances the growth of fungus and then checked for the presence of H. capsulatum. The drawback is the time it takes for the fungus to grow — two to four weeks and sometimes up to 12 weeks. For that reason, it's not a good choice in cases of disseminated disease where delayed treatment may prove fatal.
• Fungal stain. In this test, a tissue sample, which may be taken from sutum, bone marrow, your lungs or a skin sore, is stained with dye and examined under a microscope. The accuracy of the test depends on the type of sample obtained and the skill and experience of the examiner. Other organisms can resemble H. capsulatum under the microscope, so confirmation with another test is desirable if an organism resembling H. capsulatum is identified.
• Serology. This test examines blood for antigens and antibodies. It's a quick and fairly accurate way of detecting disseminated histoplasmosis as well as chronic or mild cases of the disease. But false-negative results are a problem, especially in people who have compromised immune systems or are infected with other types of fungi. The test can also be positive in people who live in endemic areas and have had past exposure to H. capsulatum, even though their current symptoms may be due to something else.

Depending on your signs and symptoms and the severity of your illness, your doctor may recommend other tests, such as:

• Chest X-ray. Although not normally used to diagnose histoplasmosis, an ordinary chest X-ray can show inflammation and damage in your lungs.
• Computerized tomography (CT). This X-ray technique produces more detailed images than do standard X-rays. CT can be especially helpful for detecting complications from histoplasmosis.
• Bronchoscopy. Your doctor may use this test to help establish a diagnosis of histoplasmosis if the disease hasn't already been confirmed by a fungal culture, stain or serology test. During the procedure, your doctor examines your windpipe (trachea) and the air passages leading to your lungs using a thin, lighted tube (endoscope). A small sample of tissue (biopsy) can be taken through the endoscope.

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Histoplasmosis can cause a number of serious complications, even in otherwise healthy people. For infants, older adults and people with compromised immune systems, the potential problems are often life-threatening.

Complications of acute and chronic pulmonary histoplasmosis

• Enlarged lymph nodes. Most people with histoplasmosis have some involvement with the lymph nodes in the central part of the chest. This region lies between your lungs and contains the trachea, esophagus, heart and many small lymph nodes. In a small percentage of people with acute pulmonary histoplasmosis, the lymph nodes may enlarge enough to obstruct the airways or esophagus, making it difficult to breathe or swallow. Sometimes the pulmonary arteries and veins — the large blood vessels in the lungs — also may be blocked.
• Fibrosing mediastinitis. A rare but severe late complication of histoplasmosis, fibrosing mediastinitis occurs when scar tissue from lymph nodes in the chest invades and blocks adjoining structures, especially the esophagus and large blood vessels. Signs and symptoms, such as a cough that brings up blood, chest pain and breathlessness, usually don't appear until the disease is quite advanced. When structures in both lungs are affected, fibrosing mediastinitis can be life-threatening.
• Pericarditis. This is inflammation of the pericardium, the sac that surrounds your heart. Normally, this sac contains a small amount of fluid. But when the pericardium becomes inflamed, the amount of fluid in the sac may increase. This can interfere with the heart's ability to pump blood efficiently. Pericarditis that occurs as a complication of histoplasmosis usually results from inflammation in nearby lymph nodes, rather than from infection of the pericardium itself.
• Arthritis. Joint inflammation, often in conjunction with a skin rash (erythema nodosum), is a common complication of acute pulmonary histoplasmosis. Women are far more likely to be affected than are men. Although the arthritis may persist for months, it usually clears on its own or after a brief course of nonsteroidal anti-inflammatory drugs.

Complications of disseminated histoplasmosis
Disseminated histoplasmosis can affect almost any organ system in your body, leading to a number of serious and potentially fatal complications. Some of these include:

• Adrenal insufficiency. Your adrenal glands, which are located just above your kidneys, produce hormones that give instructions to virtually every organ and tissue in your body. When the glands don't provide enough of these hormones, serious, and potentially life-threatening, problems can occur. Untreated adrenal insufficiency (Addison's disease) is fatal.
• Meningitis. An infection and inflammation of the membranes (meninges) and fluid (cerebrospinal fluid) surrounding your brain and spinal cord, meningitis can be life-threatening. The disease usually strikes suddenly, often with a high fever, severe headache and vomiting. As it progresses, the brain swells and may begin to bleed. Meningitis is fatal in a small percentage of cases. As a complication of histoplasmosis, meningitis occurs primarily in people with compromised immune systems, although it occasionally develops in otherwise healthy people.

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Treatment usually isn't necessary if you have a mild case of acute histoplasmosis. But if your symptoms are severe or you have the chronic or disseminated forms of the disease, you'll likely need treatment with one or more antifungal medications — most often amphotericin B (Fungizone IV) and itraconazole (Sporanox). The specific drug and the length of treatment depend on the type and severity of your illness as well as on your overall health.

In general, one of several formulations of amphotericin B is the initial treatment of choice for people with disseminated histoplasmosis or severe disease. But because these drugs can be toxic to the kidneys and must be administered intravenously, doctors usually switch to itraconazole within a few days to a few weeks, depending on how your condition improves. Corticosteroids are also sometimes given initially if you have severe respiratory disease and difficulty maintaining oxygen levels in your bloodstream.

Itraconazole alone may be effective in mild cases of disseminated histoplasmosis as well as in chronic pulmonary disease. Although itraconazole doesn't work as quickly as amphotericin B, it has fewer side effects and can be taken in pill form. While using this medication, you may experience headache, dizziness, nausea, vomiting or diarrhea, but these symptoms often go away over time. If you have a history of liver or kidney problems, or another lung disease, you'll need to be monitored closely during treatment.

If you're not a candidate for itraconazole or can't tolerate the medication, your doctor may prescribe fluconazole (Diflucan), another antifungal drug. Fluconazole isn't as effective as itraconazole, however, and you're more likely to experience a relapse with this medication.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

It's difficult to prevent exposure to the fungus that causes histoplasmosis, especially in parts of the country where the disease is widespread. Even so, these steps can help reduce the risk of infection:

• Spray contaminated soil. Before you work in or dig soil that's likely to harbor H. capsulatum, spray it thoroughly with water. This can help prevent spores from being released into the air. Spraying chicken coops and barns before cleaning them also can reduce your risk.
• Use an effective face mask. This is the best way to protect yourself from soil-borne organisms if you must work in contaminated areas or in caves known to harbor bats. The National Institute for Occupational Safety and Health (NIOSH) recommends using Part 84 particulate respirators certified by NIOSH.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.