Aspergillus Mold, Aspergillosis, and Human Health
What Is Aspergillus?
Aspergillus is a mold that can be found in many habitats around the world. Some species of Aspergillus have important uses, but others can live on or in the human body and cause disease. The disease usually takes the form of a respiratory disorder. Unfortunately, in some people the mold can become invasive and cause a life threatening infection. An infection produced by Aspergillus is known as aspergillosis.
Like other molds, Aspergillus is a type of fungus. Its body consists of thin, branching filaments called hyphae. When they're mature, the hyphae produce reproductive spores that travel to other areas, where they germinate to produce new hyphae.
Aspergillus spores typically enter the human body by inhalation. If a person has a functioning immune system the spores are generally destroyed. If the spores do manage to germinate the resulting hyphae stay inside the airways and don't travel further into the body. In some people with a damaged immune system, however, the hyphae are able to invade deeper body structures and organs, causing a very serious infection.
The term "aspergillosis" refers to a spectrum of disorders. Three important types of aspergillosis are Allergic Bronchopulmonary Aspergillosis, (ABPA), Chronic Pulmonary Aspergillosis (CPA), and Invasive Aspergillosis.
Some Helpful Species of Aspergillus
Although molds have a bad reputation, some species—including species of Aspergillus—can be helpful, at least under certain conditions. For example:
- Aspergillus niger produces citric acid, which is used in the processed food industry.
- Aspergillus oryzae plays an essential role in the production of the Japanese beverage known as sake.
- Aspergillus terreus produces useful industrial chemicals as well as lovastatin, a medication that lowers our blood cholesterol level.
Unfortunately, some mold species can be harmful for humans instead of helpful. In addition, some species can be helpful in certain situations and harmful in others.
Respiratory System Diagram
There are many species of Aspergillus. The mold usually grows in areas which have a good oxygen supply, such as on the surface of bread, on stored grain and dead leaves, and in compost and soil. Some species are helpful, some have no obvious effect on our lives, some are harmful, and some can be either helpful or harmful, depending on where they are growing.
In humans, Aspergillus may colonize skin wounds, the lungs, the sinuses, and parts of the body without a blood supply, such as the cornea of the eye and the ear canal. The fungus may also infect fingernails and toenails. Sometimes Aspergillus is present in internal organs, causing serious health effects.
It’s hard for us to avoid Aspergillus spores. They are transported through the air and can be found in soil, air conditioning units, heating ducts, dust, water, and food. They may also be found in animal dung and bird droppings.
Aspergillus isn't dangerous for most of us, but it can interfere with some people's lives. The mold can make asthma worse, for example, and can make breathing difficult in people with certain medical conditions. In some people an Aspergillus infection is very dangerous.
Someone with symptoms that might suggest the presence of aspergillosis or another mold infection should visit a doctor for a diagnosis and treatment.
Effect of Asthma on the Airways
Allergic Bronchopulmonary Aspergillosis (ABPA)
Aspergillus spores may cause an allergic reaction in some asthmatics or in some people suffering from other respiratory system diseases, such as cystic fibrosis. The person's immune system overreacts to the presence of the spores, causing the airways to become inflamed. This condition is known as allergic bronchopulmonary aspergillosis, or ABPA.
The spores may germinate in the respiratory system, causing hyphae to grow in the mucus of the airways. In ABPA the fungal hyphae stay in the air passages and don't travel further into the body, however.
Symptoms of allergic bronchopulmonary aspergillosis may include increased and worsening asthma attacks and increased mucus production. The patient sometimes coughs up brown mucus and blood. In severe cases, the person may also suffer from a fever, a headache, and weight loss and may feel generally unwell.
Doctors often prescribe corticosteroids to reduce the overactivity of the immune system and the inflammation, which can damage the lungs. Any mucus plugs in the air passages are removed. Antifungal medications may also be prescribed. This treatment usually relieves the symptoms of ABPA. However, there may be a flare-up of the infection and symptoms at a later date, which require more treatment.
Until recently, ABPA was thought to be a rare condition, but today some researchers think that it may be more common than originally believed.
White Blood Cells Destroy Aspergillus Spores
Aspergillus produces specialized stalks called conidiophores. At the tip of a conidiophore is a ball containing spores. The spores are known as conidia. A spore can produce hyphae once it lands in a suitable area.
Chronic Pulmonary Aspergillosis (CPA)
In chronic pulmonary aspergillosis, or CPA, Aspergillus is able to colonize areas in the respiratory system, producing a chronic (long lasting) condition. One area that may be colonized is a cavity that has formed in the lungs. Cavities form when lung tissue is destroyed by a disease such as tuberculosis.
An aspergilloma is a ball of fungal hyphae which develops inside a lung cavity. The aspergilloma is hidden from the immune system, except where it touches healthy lung tissue.
Chronic Pulmonary Aspergillosis usually affects people who have another chronic lung disease, a health problem such as alcoholism, or a weakened immune system. CPA may cause no symptoms, but the patient may cough up blood if blood vessels are damaged by the fungal growth. Other symptoms may include a cough, breathlessness, chest pain, fatigue, and weight loss.
Patients with CPA are generally treated with antifungal medications. Aspergillomas may be removed surgically.
Aspergillus and Aspergillosis
Invasive Aspergillosis is the most serious form of Aspergillus infection. An invasive infection is very dangerous and requires intense treatment. This condition nearly always develops when the person’s immune system is severely weakened and isn't functioning well enough to destroy or limit the growth of the mold. The mold penetrates tissues from its initial infection site and enters organs. Tissues and organs that may be infected include blood and the liver, kidneys, heart, and brain. The infection often progresses rapidly.
Invasive Aspergillosis: Possible Causes and Symptoms
Conditions which might lead to the development of invasive aspergillosis include treatment by drugs that suppress the immune system after a person has received a transplant (immunosuppressive drugs), advanced AIDS, and long term use of corticosteroids. Corticosteroids are useful medications for relieving inflammation, but they also suppress the activity of the immune system.
Neutrophils are white blood cells that effectively fight fungi. Any condition that destroys neutrophils or prevents their formation increases the risk of developing invasive aspergillosis. Example of these conditions include some types of chemotherapy, high doses of chemotherapy drugs, leukemia, and radiation therapy applied to bones. Radiation may interfere with neutrophil production because it can damage the bone marrow cells that make the blood cells.
Symptoms of invasive aspergillosis include chest pain, a very bloody cough, shortness of breath, headache, fever, and chills. (These symptoms may indicate the presence of another condition instead of aspergillosis. A doctor's diagnosis is needed to identify the cause of the symptoms.) Some symptoms depend on the part of the body affected. Meningitis may be caused by fungal invasion of the brain and endocarditis may develop after fungal invasion of the heart. If the kidneys are infected there may be decreased urine production.
New Aspergillosis Treatments From Manchester University
Some Possible Treatments
There are several types of antifungal drugs that doctors can prescribe for people suffering from invasive aspergillosis. Sometimes these drugs are given as a preventative measure when people receive transplants or medical treatments known to reduce the activity of the immune system. Medications in the azole group are often prescribed. Unfortunately, Aspergillus is becoming resistant to azoles. In addition to the use of medicines, doctors try to find ways to reduce immunosuppression in patients who develop invasive aspergillosis so that the patient’s immune system can help fight the fungus.
Preventing the Growth of Aspergillus niger
Tips for Avoiding Aspergillosis
Most of us are constantly being exposed to Aspergillus spores, but the spores generally create no health problems. It’s still a good idea to reduce exposure to the fungus whenever possible, especially if we suffer from another health problem.
Some steps which will help are shown below.
- Avoid damp areas and standing water.
- Stay away from compost and decaying plants.
- Reduce the humidity in buildings.
- Maintain clean heating ducts and air conditioners.
- Keep the dust level in buildings low.
- Use HEPA filters when ventilating enclosed areas and in devices such as vacuum cleaners. These filters remove fine particles from the air.
- Avoid gardening and mowing the lawn if you are at high risk for developing aspergillosis.
People with pre-existing medical conditions should follow their doctor's instructions carefully in order to avoid or reduce their exposure to Aspergillus spores. Doing so may enable a person to avoid a potentially nasty and sometimes dangerous illness.
© 2011 Linda Crampton