Introduction

The aspergillus species includes more than 150 types of mold that occur widely in the indoor and outdoor environment. Although most of the molds are harmless, a few can cause serious illnesses in people with a weakened immune system, underlying lung disease or asthma. These illnesses, collectively called aspergillosis, range from allergic responses to severe and sometimes fatal infections.

Aspergillosis begins when susceptible people inhale mold spores into their lungs. In some people, the spores trigger an allergic reaction. Other people develop mild to serious lung infections. The most deadly form of aspergillosis — invasive aspergillosis — occurs when the infection spreads beyond the lungs to other organs. Even when discovered and treated early, invasive aspergillosis is often fatal.

Aspergillosis infections are treated with antifungal agents, though not always successfully and often with serious side effects. In 2005, British researchers cracked the genetic code of aspergillus molds. The hope is that this knowledge will lead to better ways of diagnosing and treating aspergillosis.

Signs and symptoms

The signs and symptoms of aspergillosis vary with the type of infection.

Allergic bronchopulmonary aspergillosis

Some people with asthma or cystic fibrosis have an allergic reaction to aspergillus mold. Signs and symptoms of this condition, known as allergic bronchopulmonary aspergillosis, include:

• Fever

• A general feeling of being unwell (malaise)

• A cough that may bring up blood or plugs of mucus

• Wheezing

• Worsening asthma

Aspergilloma

People whose lungs have been damaged by emphysema, tuberculosis or other diseases that leave air spaces (cavities) in the lungs may develop a pulmonary aspergilloma — a tangled ball of fungus fibers that forms in these spaces. Initially, an aspergilloma may not produce symptoms, but over time, it can cause:

• A cough that often brings up blood

• Chest pain

• Wheezing

• Shortness of breath

• Unintentional weight loss

Invasive pulmonary aspergillosis

The most severe form of aspergillosis, invasive pulmonary aspergillosis, occurs when the infection spreads rapidly through your bloodstream to your brain, heart, kidneys or skin. Signs and symptoms depend on which organs are affected, but in general, invasive aspergillosis can cause:

• Fever and chills

• Headaches

• Bloody cough

• Shortness of breath

• Chest or joint pain

• Massive bleeding from your lungs

Other aspergillus infections

Aspergillus can invade your sinuses and ear canals as well as your lungs. In your sinuses, it can cause a stuffy nose, drainage, inflammation, fever, facial pain and headache. Ear canal infections can cause itching, drainage and pain.

Causes

Aspergillus plays an indispensable role in the ecosystem by breaking down organic matter. It's also virtually unavoidable. Outdoors, it's found in decaying leaves and compost and on plants, trees and grain crops. Inside, the spores — the reproductive parts of mold — thrive in air conditioning and heating ducts, insulation, carpeting, ornamental plants, tap water, dust and food — especially ground pepper and other spices.

Everyday exposure to aspergillus is rarely a problem for people with healthy immune systems. When mold spores are inhaled, immune system cells simply surround and destroy them. But people who have a weakened immune system from illness or medications have fewer infection-fighting cells. This allows aspergillus to take hold, invading the lungs, and in the most serious cases, other parts of the body.

Risk factors

Your risk of developing aspergillosis depends on your overall health and the extent of your exposure to mold, but in general, these factors make you more vulnerable to infection:

• Weakened immune system. This is the greatest risk factor for invasive aspergillosis. People taking immune-suppressing drugs after undergoing transplant surgery, especially bone marrow or stem cell transplants, are the most severely affected. In fact, aspergillosis is the leading cause of death among people who have received a transplant. People with later-stage AIDS also may be at increased risk.

• Low white blood cell level. White blood cells called neutrophils play a key role in fighting fungal infections. Having a very low level of these cells (neutropenia) due to chemotherapy, an organ transplant or leukemia makes you much more susceptible to invasive aspergillosis. So does having chronic granulomatous disease — an inherited disorder that affects immune system cells.

• Lung cavities. An aspergilloma develops when mold spores germinate in a healed air space (cavity) in your lungs. Cavities are areas that have been damaged by serious lung diseases such as tuberculosis or sarcoidosis — an illness that causes inflammation in your lungs and other organs. The larger the cavity, the greater your chance of developing an aspergilloma. Most often, aspergillomas don't spread beyond the cavity, but when they do, they can cause a cough that brings up blood, and the bleeding may be severe.

• Asthma or cystic fibrosis. About 7 percent of people with asthma and cystic fibrosis have an allergic response to aspergillus mold. This is more likely to occur in people whose lung problems are long-standing or hard to control.

• Long-term corticosteroid therapy. Because corticosteroids suppress your immune system, they increase the risk of aspergillosis. Infections that result from corticosteroid use tend to be severe and to progress rapidly.

• A hospital stay. Aspergillus mold is found on many hospital surfaces — bedrails, plants, surgical instruments, air conditioning ducts, insulation and in tap water. Though healthy people aren't likely to be affected, people with a weakened immune system or serious illness are highly susceptible to infection. Most major hospital outbreaks have been traced to hospital construction and renovation projects, and to contaminated air filters and carpeting.

• Genetics. Some researchers speculate that genetic factors may make certain people more prone to aspergillosis infection.

When to seek medical advice

If you have asthma or cystic fibrosis, see your doctor whenever you notice a change in your symptoms. Although aspergillosis may not be the cause, it's important to have any problems evaluated. If you have a weakened immune system and develop shortness of breath, a cough that brings up blood, or an unexplained fever, get immediate medical care. In the case of invasive aspergillosis, prompt treatment is so crucial that treatment is often started before the infection is definitively diagnosed.

Screening and diagnosis

Diagnosing aspergillosis can be difficult. Aspergillus is common in the environment and is sometimes found in the saliva and sputum of healthy people. What's more, it's hard to distinguish aspergillus from other molds under the microscope, and symptoms of the infection are similar to those of conditions such as tuberculosis.

To arrive at an accurate diagnosis, your doctor is likely to use one or more of the following tests:

• Imaging tests. A chest X-ray or computerized tomography (CT) scan — a type of X-ray that produces more detailed images than conventional X-rays do — can usually reveal an aspergilloma as well as characteristic signs of invasive and allergic aspergillosis.

• Sputum stain and culture. In this test, a sample of your sputum is stained with a dye and checked for the presence of aspergillus filaments. The specimen is then placed on a medium that encourages the mold to grow.

• Skin and blood tests. Diagnosing allergic bronchopulmonary aspergillosis usually requires skin and blood tests. For the skin test, a small amount of aspergillus antigen is injected into your forearm. If you have antibodies to the mold in your bloodstream, you'll develop a hard, red bump at the injection site. Blood tests look for elevated levels of certain antibodies, indicating an allergic response.

• Biopsy. Examining a sample of tissue from your lungs or sinuses under a microscope is usually necessary to confirm a diagnosis of invasive aspergillosis.

Complications

Depending on the type of infection, aspergillosis can cause a variety of serious complications:

• Bone loss and spread of infection. An aspergillus infection in your sinuses can destroy facial bones. It can also spread beyond your sinuses, and may be life-threatening if you have a severely impaired immune system.

• Bleeding. Both aspergillomas and invasive aspergillosis can cause massive, and sometimes fatal, bleeding in your lungs.

• Systemic infection. The most devastating complication of aspergillosis is the spread of the infection to other parts of your body, especially your brain, heart and kidneys. Invasive aspergillosis spreads rapidly and is often fatal in spite of early treatment.

Treatment

There's no universally effective therapy for aspergillosis. Available treatments vary with the type of disease:

• Oral corticosteroids. The goal in treating allergic bronchopulmonary aspergillosis is to prevent existing asthma or cystic fibrosis from becoming worse. The best way to do this is with oral corticosteroids. Antifungal medications by themselves aren't helpful for allergic aspergillosis, but they may be used in combination with corticosteroids to reduce the dose of steroids and improve lung function.

• Antifungal medications. These drugs are the standard treatment for invasive pulmonary aspergillosis. Historically, the drug of choice has been amphotericin B, but the newer medication voriconazole is now preferred because it appears more effective and may have fewer side effects. All antifungals can cause serious problems, however, including kidney and liver damage, and they frequently interact with other medications given to people who have weakened immune systems.

• Watchful waiting. Aspergillomas often don't need treatment, and may simply be closely monitored. When they cause life-threatening bleeding, the options are limited. Because antifungal medications aren't effective against aspergillomas, surgery is the first choice. The surgery is risky, however, and your doctor may suggest another option, which involves threading a small catheter into the artery that supplies blood to the cavity containing the fungus ball. Though this procedure can stop massive bleeding, it doesn't prevent it from recurring.

Prevention

It's nearly impossible to avoid aspergillus entirely, but if you've had a transplant or are undergoing chemotherapy, try to stay away from the most obvious sources of mold such as construction sites, compost piles and stored grain.

Hospitals, for their part, are taking increasingly aggressive measure to protect patients, including using barriers around areas under construction, monitoring air and air filters for spores, minimizing exposure to carpet cleaning and vacuuming, and carefully maintaining ventilation systems.