Allergic bronchopulmonary aspergillosis is a lung condition that occurs when the immune system overreacts to a common fungus found in soil and decaying plants, causing inflammation and breathing problems in people with asthma or cystic fibrosis.

Understanding Allergic Bronchopulmonary Aspergillosis

Allergic bronchopulmonary aspergillosis, often abbreviated as ABPA, is a fungal infection of the lung that results from a hypersensitivity reaction, which means the body’s immune system responds too strongly to something that would normally be harmless. This reaction happens when a person breathes in spores from a fungus called Aspergillus fumigatus. The fungus does not actually invade the lung tissue like a typical infection. Instead, it settles in the airways and triggers an allergic response that causes swelling, narrowing of the air passages, and buildup of thick mucus.^[1]

The condition primarily affects people who already have certain lung diseases. When someone with asthma or cystic fibrosis inhales Aspergillus spores, their airways may become colonized by the fungus. The thick, sticky mucus that is characteristic of these conditions makes it difficult for the body to clear the spores naturally. Over time, the immune system mounts a vigorous defense, producing antibodies and other immune cells that attack the fungus. Unfortunately, this immune response also damages the airways themselves, leading to episodes of worsening asthma symptoms, coughing, and sometimes permanent lung damage if left untreated.^[2]

While ABPA can sound alarming, it is important to understand that this is not the same as invasive aspergillosis, a serious infection that occurs in people with severely weakened immune systems. ABPA is also different from an aspergilloma, which is a ball of fungus that grows in pre-existing lung cavities. With proper treatment and monitoring, many people with ABPA can manage their symptoms effectively and maintain a good quality of life.^[6]

How Common Is This Condition?

Allergic bronchopulmonary aspergillosis most commonly appears in people between their third and fifth decades of life, meaning it typically develops when people are in their twenties through their fifties. However, the condition can also occur in children. It is usually found in individuals with severe asthma or those living with cystic fibrosis.^[1]

Not everyone who is allergic to Aspergillus will develop ABPA. Studies show that about one quarter of people with asthma test positive for an allergy to Aspergillus when a skin prick test is performed, and about half of people with cystic fibrosis show this sensitivity. However, actual ABPA is less common. The prevalence of ABPA among people with asthma is approximately 13 percent, while among those with cystic fibrosis it is around 9 percent. Worldwide, more than four million people are affected by this condition.^[1]

Understanding how many people are affected helps researchers and healthcare providers allocate resources and develop better treatments. It also reassures patients that they are not alone in dealing with this condition, and that medical professionals have substantial experience managing it.

What Causes ABPA?

The root cause of allergic bronchopulmonary aspergillosis is exposure to Aspergillus species, which are molds found everywhere in the environment. These fungi are particularly abundant in organic matter such as compost heaps, fallen leaves, soil, and decaying vegetation. Aspergillus is also commonly present in indoor environments, including air-conditioning systems, ventilation ducts, and damp areas of buildings.^[1]

There are over 100 species of Aspergillus worldwide, but most cases of illness in humans are caused by a few specific types: Aspergillus fumigatus, Aspergillus niger, Aspergillus flavus, and Aspergillus clavatus. Among these, Aspergillus fumigatus is by far the most common culprit in ABPA. The spores of this fungus, called conidia, are extremely small, measuring only two to three micrometers in diameter. Because of their tiny size, these spores easily travel deep into the lungs when inhaled, reaching the smallest air sacs called alveoli where they can settle.^[1]

Once the spores are in the lungs, they encounter the immune system. In most healthy people, the immune system either ignores the spores or clears them without causing problems. However, in people with asthma or cystic fibrosis who are allergic to Aspergillus, the immune system recognizes the fungus as a dangerous invader. This triggers multiple types of immune responses, including the production of antibodies called IgE and IgG, as well as activation of immune cells. These reactions cause inflammation, which leads to airway narrowing, increased mucus production, and tissue damage over time.^[12]

Research has also identified a genetic component to ABPA. Certain molecules on the surface of immune cells, called HLA-DR molecules, appear to influence susceptibility. Specifically, HLA-DR2, DR5, and possibly DR4 or DR7 contribute to increased risk, while HLA-DQ2 appears to offer some protection. The combination of these genetic factors may determine whether someone with asthma or cystic fibrosis will develop ABPA after exposure to Aspergillus.^[1]

Who Is at Higher Risk?

The biggest risk factor for developing allergic bronchopulmonary aspergillosis is having an underlying lung condition, particularly asthma or cystic fibrosis. People with these conditions have airways that produce extra mucus and have difficulty clearing it. This creates an environment where Aspergillus spores can become trapped and begin to colonize the airways. The fungus does not invade the tissue but lives on the surface of the airways, constantly stimulating the immune system.^[2]

People with uncontrolled or severe asthma are particularly vulnerable. When asthma is not well-managed, the airways are already inflamed and reactive, making them more likely to respond strongly to the presence of Aspergillus. Similarly, individuals with cystic fibrosis have thick, sticky mucus that is difficult to clear, creating an ideal situation for fungal colonization.^[4]

Having other allergic conditions may also increase risk. Many people with ABPA also suffer from other allergic diseases such as atopic dermatitis (a type of eczema), urticaria (hives), allergic rhinitis (hay fever), and sinusitis (inflammation of the sinuses). This suggests that people with a generally overactive or allergy-prone immune system may be more susceptible to developing ABPA when exposed to Aspergillus.^[2]

Environmental factors play a role as well. People who live or work in environments with high levels of mold and dampness may have greater exposure to Aspergillus spores. This includes those who work with compost, gardening, or in agricultural settings, as well as people living in buildings with water damage or poor ventilation. However, because Aspergillus is so common in the environment, complete avoidance is nearly impossible.^[16]

Recognizing the Symptoms

The symptoms of allergic bronchopulmonary aspergillosis often overlap with those of asthma, which can make the condition challenging to recognize at first. For someone who already has asthma, the most noticeable change is usually a progressive worsening of their usual asthma symptoms. Wheezing becomes more frequent or severe, and shortness of breath may occur even with activities that were previously manageable. These symptoms represent the airways becoming more inflamed and constricted due to the allergic reaction to Aspergillus.^[2]

One of the characteristic features of ABPA is a productive cough, meaning a cough that brings up mucus or sputum. This mucus often has a distinctive appearance, described as brownish or containing brown flecks. Some people cough up thick mucus plugs, which are solid or semi-solid chunks of mucus that have blocked airways. In some cases, the mucus may contain blood, which can be alarming but occurs because the inflamed airways are fragile and prone to minor bleeding.^[6]

People with ABPA may also experience systemic symptoms, meaning symptoms that affect the whole body rather than just the lungs. Fever can occur, often coming and going rather than being constant. General weakness or a sense of feeling unwell, called malaise, is common. Some people experience loss of appetite, which can lead to unintended weight loss. Chest pain may develop as the lungs become more inflamed, though this is less common than other symptoms.^[12]

For individuals with cystic fibrosis, ABPA symptoms may manifest as a worsening of their baseline lung function or more frequent respiratory infections. Because cystic fibrosis already causes chronic lung problems, distinguishing ABPA from other complications can be particularly challenging. This is why regular screening and monitoring are important for people with cystic fibrosis who may be at risk.^[7]

How the Disease Affects the Lungs

To understand how allergic bronchopulmonary aspergillosis affects the body, it helps to know a bit about normal lung structure. The lungs consist of a branching network of airways that carry air in and out. The largest airway is the trachea, or windpipe, which splits into two main tubes called bronchi, one for each lung. These bronchi divide into smaller tubes called bronchioles, which eventually end in tiny air sacs called alveoli where oxygen and carbon dioxide are exchanged with the blood.^[19]

In ABPA, the immune system’s reaction to Aspergillus causes several changes in the airways. First, the muscles surrounding the bronchioles go into spasm, causing them to narrow. This is similar to what happens during an asthma attack and leads to wheezing and difficulty breathing. At the same time, the lining of the airways becomes inflamed and swollen, which further reduces the space available for air to flow through.^[1]

The inflammation also triggers the airways to produce excessive amounts of mucus. Normally, mucus helps trap particles and germs, and tiny hair-like structures called cilia sweep the mucus up and out of the lungs. However, in ABPA, the mucus becomes thick and sticky, making it difficult to clear. This mucus can plug up airways, causing sections of the lung to collapse or develop atelectasis, which means the lung tissue is not fully expanded and cannot participate in breathing.^[12]

Over time, repeated episodes of inflammation can cause permanent damage to the airways. The walls of the bronchi and bronchioles can become scarred and thickened, a process called fibrosis. The airways may also become abnormally widened and damaged, a condition known as bronchiectasis. When bronchiectasis develops, the airways lose their normal structure and function, making it even harder to clear mucus and increasing the risk of bacterial infections. In severe cases, these changes can significantly impair lung function and lead to respiratory failure.^[6]

Under the microscope, lung tissue from someone with ABPA shows several characteristic features. Airways are filled with thick, sticky mucus plugs. There is an increase in certain white blood cells called eosinophils, which are typically involved in allergic reactions. The spaces between the alveoli become infiltrated with immune cells, including plasma cells and other white blood cells. The airways also develop more mucus-producing cells and glands, perpetuating the cycle of mucus buildup.^[12]

Prevention Strategies

Preventing allergic bronchopulmonary aspergillosis is challenging because Aspergillus spores are so common in both indoor and outdoor environments. Most people breathe in these spores every day without any problems. However, for people at risk—particularly those with asthma or cystic fibrosis—there are some steps that may help reduce exposure and lower the chances of developing ABPA.^[16]

One of the most important strategies is to control asthma or other underlying lung conditions as effectively as possible. When asthma is well-controlled with appropriate medications, the airways are less inflamed and reactive, which may make them less likely to develop an allergic response to Aspergillus. Following prescribed treatment plans, using inhalers correctly, and working with healthcare providers to adjust medications as needed are all crucial steps.^[4]

Reducing exposure to environments with high levels of mold and fungal spores can be helpful. This includes avoiding dusty areas whenever possible, such as construction sites, excavation areas, or places with visible mold growth. When avoidance is not possible, wearing a properly fitted N95 respirator mask can help filter out small particles including fungal spores. People at high risk should be cautious about activities that involve close contact with soil or decaying plant matter, such as gardening, composting, or handling hay or straw.^[16]

Maintaining good indoor air quality is another important preventive measure. This includes fixing water leaks promptly, ensuring adequate ventilation, using dehumidifiers in damp areas, and cleaning or replacing air filters in heating and cooling systems regularly. Mold tends to grow in areas with high humidity, so keeping indoor humidity levels below 50 percent can help discourage fungal growth. Regular cleaning of bathrooms, kitchens, and other areas prone to moisture can also reduce mold exposure.^[17]

For people at very high risk, such as those with severe asthma or cystic fibrosis, healthcare providers may recommend preventive antifungal medications in certain situations. However, this is not standard practice for most people. Regular monitoring and screening for ABPA in high-risk populations allows for early detection and treatment, which can prevent complications. Some transplant patients or those with severe immunocompromising conditions may benefit from antifungal prophylaxis, though this is determined on a case-by-case basis.^[16]