Alternaria alternata is one of the most widespread species of mold found across the globe. This microscopic fungus belongs to the genus Alternaria and is known for its ability to thrive in diverse conditions. Its colonies are typically dark, with a greenish-black or olive-brown pigmentation, reflecting its classification as a dematiaceous (dark-colored) fungus. The organism produces massive quantities of airborne spores, making it a significant environmental concern for both agricultural health and human respiratory well-being.
Biological Profile and Habitat
Alternaria alternata functions as both a saprophyte and a pathogen. As a saprophyte, it plays a part in the ecosystem by breaking down dead and decaying organic matter, contributing to the decomposition cycle. It is also a well-known plant pathogen, capable of infecting over 380 host species and causing diseases like leaf spots and blights on crops.
This mold thrives in a broad range of temperatures, with optimal growth occurring between 25 and 29 degrees Celsius. The spores, or conidia, are the primary means of dispersal and are characteristically large, dark, and multicellular, often developing in chains. These spores are readily picked up by wind currents outdoors, which is where the highest concentrations are typically found.
Spores enter structures through open windows, ventilation systems, or on clothing and pets. Once inside, A. alternata needs moisture and a suitable food source to establish a colony, often colonizing damp areas like window frames, textiles, and water-damaged building materials. The presence of indoor colonies is a clear indication of a moisture issue, as the mold rapidly grows in places with high humidity or water intrusion.
Health Effects of Exposure
The most common health consequence associated with A. alternata is a hypersensitive reaction triggered by inhaling its airborne spores. These spores carry potent allergens that provoke an immune response in sensitized individuals. Exposure often leads to symptoms of allergic rhinitis, commonly known as hay fever, including persistent sneezing, nasal congestion, and a runny nose.
The allergens can also affect other mucous membranes, causing allergic conjunctivitis, which manifests as itchy and watery eyes. Individuals with a pre-existing sensitivity may also experience irritation of the throat and dry, scaly skin. The allergic reaction is an inflammatory cascade aimed at eliminating the perceived foreign threat of the inhaled fungal material.
A. alternata is particularly recognized for its strong association with asthma exacerbation, especially in children. Sensitivity to this mold is a significant risk factor for severe, potentially life-threatening, asthma attacks. Once inhaled, the mold spores and their fragments can penetrate deep into the airways, causing chronic inflammation and bronchial hyperresponsiveness. Chronic or high-level exposure can also contribute to the development of more serious conditions, such as hypersensitivity pneumonitis, which is an inflammation of the lung tissue.
Toxin Production
Distinct from allergic reactions, A. alternata produces secondary metabolites called mycotoxins. This species can generate over 70 different toxic compounds, which are primarily studied for their effects following ingestion rather than inhalation. The fungus creates these toxins when it infects crops in the field or during storage, leading to contaminated food products.
The most significant Alternaria mycotoxins include Alternariol (AOH), Alternariol Monomethyl Ether (AME), and Tenuazonic Acid (TeA). These compounds belong to different chemical classes, each with distinct toxicological properties. Their presence is a concern because A. alternata commonly contaminates various food sources, including grains, oilseeds, tomatoes, and citrus fruits.
Exposure occurs when humans or animals consume contaminated agricultural products. Alternaria toxins are classified as emerging contaminants due to their potential health risks. Studies indicate that chronic ingestion of these compounds may be associated with cytotoxic and genotoxic effects on human cells. Furthermore, some toxins, like AOH, have been linked to potential endocrine disruption due to their structural similarity to estrogen.
Management and Removal
Controlling the health effects of A. alternata begins with aggressively managing the fungus in the indoor environment. Since moisture is the most important factor for its growth, the immediate priority is identifying and repairing any water leaks or sources of intrusion. Without eliminating the moisture problem, cleaning or removing the mold will only provide a temporary solution.
Maintaining a low indoor humidity level is a fundamental preventative step, targeting relative humidity below 60 percent. Preventative measures include:
- Using dehumidifiers.
- Ensuring proper ventilation in high-moisture areas like bathrooms and kitchens.
- Running air conditioning during humid months.
- Regularly cleaning common damp spots like window sills and shower areas.
For small surface areas of visible mold, remediation can often be handled by the occupant using a simple detergent and water solution to scrub the affected material. The mold must be completely removed, and the underlying material must be dried within 24 to 48 hours to prevent regrowth. When an infestation is extensive, covers an area larger than ten square feet, or involves the Heating, Ventilation, and Air Conditioning (HVAC) system, professional remediation services are necessary to safely contain the spores and correct the underlying cause.