What is Aspergillus
Aspergillus is a group of molds, of which about 200 species have been identified. Aspergillus molds are found throughout the world and are the most common type of fungi in the environment. About 16 species of Aspergillus molds are known to be dangerous to humans, causing disease and infection.
Species of Aspergillus which are dangerous include:
- Aspergillus clavatus
- Aspergillus flavus
- Aspergillus fumigatus
- Aspergillus glaucus
- Aspergillus nidulans
- Aspergillus niger
- Aspergillus oryzae
- Aspergillus terreus
- Aspergillus ustus
- Aspergillus versicolor
Aspergillus niger is the most abundant species of Aspergillus in nature as it can grow on a large variety of substances. Aspergillus niger can even grow in environments with very little nutrients available. In houses it is often found growing on damp walls.
Of the Aspergillus species, Aspergillus niger infects humans the third most often. A fungal ball in the lungs is eventually created by Aspergillus niger after it infects a person’s lungs and begins to grow. The health effects of Aspergillus niger include hearing problems and even hearing loss.
Aspergillus niger is black on the surface and white or yellow underneath.
Aspergillus flavus produces the carcinogenic mycotoxin, aflatoxin which often contaminates foods such as nuts. After Aspergillus fumigatus, Aspergillus flavus is the second most common Aspergillus mold to infect humans.
The surface of Aspergillus flavus is yellow-green in color and it is gold or red brown underneath.
Aspergillus fumigatus causes infection in humans more often than any other Aspergillus species. People who handle or who are exposed extensively to Aspergillus fumigatus often develop a hypersensitivity to it so that they develop severe allergic reactions to the mold.
Aspergillus fumigatus is often found growing in decomposing organic material. Of all the Aspergillus species, Aspergillus fumigatus is the most tolerant to temperature and can grow in environments between 20 degrees Celsius and 55 degrees Celsius.
Aspergillus fumigatus can be identified by the blue-green or gray color of its surface and appears white or tan underneath.
Since Aspergillus spores are everywhere, we are constantly breathing them in. However the amount of Aspergillus spores in the air is usually within our natural tolerance levels and hence does not affect our health. If you have Aspergillus mold in your home or environment, however, the increased amount of airborne spores can lead to negative symptoms. The three main types of symptoms are:
- Allergic symptoms. Exposure to large amounts of Aspergillus spores can cause allergic reactions. People with severe asthma are often sensitive to Aspergillus and can suffer asthma attacks because of the spores.
(see the Mold Symptoms page for more information about allergic symptoms)
- Toxic symptoms. These are caused by the mycotoxins produced by some species of Aspergillus, especially Aspergillus flavus. One such mycotoxin is aflatoxin, a very potent carcinogen.
- Infection. Aspergillus species can infect people and animals and begin to grow inside them, especially in the lungs. Usually only people with weakened immune systems are susceptible to infection by Aspergillus. Aspergillus infections are categorized in the group of diseases called Aspergillosis.
The group of diseases caused by Aspergillus exposure is known as Aspergillosis. The main diseases of Aspergillosis are:
- Allergic bronchopulmonary aspergillosis
- Acute invasive aspergillosis
- Disseminated invasive aspergillosis
Allergic Bronchopulmonary Aspergillosis
Allergic bronchopulmonary aspergillosis (ABPA) is a disease where a person’s immune system is hypersensitive to Aspergillus spores. This hypersensitivity causes allergic reactions in the person when they are exposed to Aspergillus as the immune system tries to expel the spores from the body.
People with cystic fibrosis or asthma are especially vulnerable to Allergic bronchopulmonary aspergillosis, with approximately 5% of asthmatics suffering this disease at some point in their life.
Allergic bronchopulmonary aspergillosis is usually caused by Aspergillus fumigatus.
- Difficulty breathing, shortness of breath and breathlessness
- Symptoms of asthma, asthma attacks
- Coughing up mucus
- Coughing blood
- Sinusitis (infection or inflammation of the sinuses)
- Loss of appetite
- General malaise and feeling unwell
- In later stages can cause lung damage (fibrosis)
Tests for allergic bronchopulmonary aspergillosis can be performed through x-rays, skin tests or blood tests.
The treatment for allergic bronchopulmonary aspergillosis is for steroids to be taken through mouth or nasal spray. An antifungal drug called itraconazole can also help to treat the disease in conjunction with steroids.
Chronic Pulmonary Aspergillosis and Aspergillomas
This disease is caused by Aspergillus infecting the body and growing in cavities in the lungs. These cavities in the lungs would usually have to be created by a previous health problem such as tuberculosis. Once the Aspergillus mold has infected the lungs it begins to grow into a fungal ball (called an aspergilloma or mycetoma) which then makes the person sick because of the allergens or toxins it puts out into the person’s body.
At first the symptoms of an aspergilloma might not be noticeable but as time goes on it can show in health problems such as:
- Breathing problems
- Chronic coughing
- Coughing up blood
- Losing weight
Aspergillomas can be detected through x-rays or blood tests. Once a person is diagnosed with an aspergilloma it is usually treated through taking drugs such as itraconazole or voriconazole. Anti-fungal drugs may even be injected into the cavity where the aspergilloma is growing in order to fight it. In some cases surgery might even have to be performed to remove the aspergilloma from the lungs.
Aspergillus molds have a powdery texture. However the color of the mold’s surface differs from species to species and can be used to identify the type of Aspergillus.
The rate of growth can also be used to identify Aspergillus, with most species growing quite quickly. After one week of growth at around 25 degrees Celsius an Aspergillus colony will generally be 1-9 cm in diameter, however Aspergillus glaucus and Aspergillus nidulans grow more slowly and will generally be 0.5-1 cm after the same time.
Aspergillus molds thrives best in oxygen-rich environments. Aspergillus molds also grows well on materials rich in carbon which they feeds off for nutrients. However some species of Aspergillus molds can survive in environments with very little nutrients and can survive off very little moisture such as just the humidity in the air (known as xerophilic).
One common place you might find Aspergillus growing is in compost or on fallen leaves, since Aspergillus grows well on decaying vegetation. Aspergillus often also grows on still living plants and trees, and foods with starch such as potatoes and bread may frequently foster Aspergillus growth.
In buildings and the home Aspergillus often can be found growing inside dirty air conditioners. This has even been a problem in some hospitals. Aspergillus also grows well on building materials and so it might often grow on or inside walls in the home, particularly if the house is damp or has been damaged by flooding.
At the Where Mold Grows page you can find more information about where mold commonly grows in the home.
Some species of Aspergillus molds can produce mycotoxins. These Aspergillus species do not constantly produce mycotoxins but can be triggered to by factors such as stress. These mycotoxins are mostly produced by the species Aspergillus flavus.
The mycotoxins most produced by these Aspergillus molds are aflatoxins. As well as being very toxic, aflatoxins are highly carcinogenic (cancer causing) especially in animals and they have also resulted in miscarriage in animals such as sheep and cows.
Crops and foods such as peanuts and maize are often contaminated by Aspergillus leading to mycotoxins being present. There are safety limits set for the amount of aflatoxins allowed in food. However there are no similar levels set for aflatoxin concentrations in the air of buildings and there has not been enough research on them despite the fact that aflatoxins in the air are also dangerous to human health.
See Aflatoxin Mycotoxins for more information about aflatoxins.
See Mycotoxins for more information about mycotoxins in general.