Aspergillus
Meaning of Aspergillus: Nearly everyone inhales its spores daily, and whether anything follows depends almost entirely on the state of the person breathing them in.
Definition of Aspergillus
Aspergillus is a genus of common molds growing in soil, compost, damp buildings and household dust, releasing spores small enough to reach the deepest parts of the lung. Healthy airways clear them without incident. In people whose defenses are weakened or whose airways are already damaged, a handful of species cause a range of illnesses grouped together as aspergillosis.
What illnesses can it cause?
| Pattern | Who it affects | What happens |
|---|---|---|
| Invasive aspergillosis | Severely weakened immune defenses | The mold grows into lung tissue and can travel through the bloodstream to the brain and other organs |
| Chronic pulmonary aspergillosis | Lungs already scarred or cavitated | Slow destruction of lung tissue over months, with weight loss and cough |
| Aspergilloma | Anyone with an existing lung cavity | A ball of fungal material sits in the cavity and may cause coughing of blood |
| Allergic bronchopulmonary aspergillosis | Asthma or cystic fibrosis | An allergic reaction to the mold inside the airways, with wheeze, fever and plugs of mucus |
The same organism therefore behaves as an invader, a squatter or an allergen depending entirely on the ground it lands on. Allergic sinus disease and, in heavy occupational exposure, a hypersensitivity reaction in the lung tissue itself round out the list.
Who is at risk of the invasive form?
The classic setting is a very low neutrophil count lasting weeks, as after treatment for leukemia or a stem cell transplant. Organ transplant recipients, people taking high doses of steroids for long periods, those with advanced untreated HIV, and people with rare inherited defects of the cells that kill microbes are also exposed. Severe influenza and other severe viral pneumonias are now recognized to open the door in intensive care patients who were not previously immunosuppressed at all. Damage to the airway lining appears to matter as much as the state of the white cells.
Does it produce anything harmful besides infection?
One species produces aflatoxin, among the most potent naturally occurring liver carcinogens known, in stored peanuts, maize and other crops kept warm and damp. This is a food safety problem rather than an infection, and it is handled by controlling how crops are dried and stored. The genus is also put to work industrially in the manufacture of citric acid, soy sauce and several enzymes, which is a reminder that most mold species have no interest in people at all.
Used in a sentence
Cultures grew Aspergillus from the patient's respiratory specimen during evaluation of the lung infiltrate.
Good to know
Exposure to Aspergillus is universal and usually harmless, so illness caused by the mold occurs mainly in people whose immune defenses or airways are already damaged.
Word origin
Where “Aspergillus” comes from
Named for its resemblance under the microscope to an aspergillum, the instrument used to sprinkle holy water, from Latin spargere, meaning to sprinkle.