You probably inhale hundreds of airborne Aspergillus spores every day. Of the hundreds of Aspergillus species, fewer than 20 cause human disease. Among these, A. fumigatus is the leading pathogen. For example, in a hospital survey comparing airborne fungal spores with fungal isolates from patients, A. fumigatus comprised only 0.3% of airborne spores, but was isolated from 44% of patients. It is a particular risk for immunocompromised patients. But exactly how Aspergillus is able to infect us remains uncertain. A recent study suggests ways that Aspergillus impairs respiratory immunity.
Evidence from a recent study suggests that a class of Aspergillus mycotoxins – termed aflatoxins – can interfere with normal respiratory immunity; specifically, aflatoxins slow mucociliary clearance. As detailed on this blog, mucocilliary clearance is an innate immunological defense function of the nasal, sinus, and upper respiratory lining (for more on nasal and sinus anatomy, read here). This effect of reducing mucocliary clearance may further enhance pathogenesis of Aspergillus.
Now add this pathogenic mechanism to the existing mycotoxin armamentarium of Aspergillus flavis that includes:
Clearly, Aspergillus have evolved a collection of weapons to attack and invade the human respiratory epithelium. This study suggests that A. niger and A. fumigatus, despite their inability to secrete aflatoxins, do secrete other mycotoxins that damage respiratory epithelium.
What does this mean for you?
The average human inhales, on average, hundreds of these infectious Aspergillus spores daily. In fact, A. niger is commonly seen as that “black mold” on shower-curtains. But for immunocompetent people, this is insignificant: your efficient respiratory immune system, mediated by mucus and your respiratory epithelium, kills the spores before they do any damage.
However, disease can occur when the host immunity is either too weak or – paradoxically – too strong.
The first group of people is intuitive: A. fumigatus is the most common invasive mold infection in these patients, and can be lethal in high-risk groups that include those with HIV/AIDS, leukemia and recipients following stem cell transplants for blood diseases.
The second group is counter-intuitive: an overly-strong immune response to A. fumigatus antigens is associated with asthma, and aberrant responses to Aspergillus antigens have been linked to various chronic airway inflammatory diseases, including chronic “allergic fungal sinusitis.”
As readers of this blog know, I am a strong advocate of saline nasal rinses for virtually all upper respiratory ailments. Saline nasal rinsing helps eliminate particulate pollutants such as diesel exhaust and other environmental pollutants; and helps eliminate particulate pathogens including viruses, bacteria, and mold spores.
If you struggle with any respiratory ailment (rhinitis, sinusitis, asthma as examples), or include yourself in the group of immunocompromised individuals, consider adding daily saline nasal irrigations to your habits. It’s a bit like the old snake-oil remedies… “good for what ails you.” Except I’m not that snake-oil salesman – I’m not selling you the remedy, simply encouraging your optimal health.
The saline nasal rinse system that I use is Nasopure (I have no financial or other relationship with Nasopure – they are simply the best available).
Regardless of which group you belong to, there is growing evidence that Aspergillus impairs respiratory immunity, or at least causes abnormal immune responses.
- Fungal aflotoxins reduce respiratory mucosal ciliary function. Lee RJ, et al., 2016: Nature Scientific Reports 6.
- Aspergillus fumigatur: Principles of pathogenesis and host defense. Holl TM, Feldmesser M., 2007: Eukaryotic Cell 6.
- Aspergillus species from hospital air and patients. Schmitt HJ, et al., 2990: Mycoses 11-12.