Alternaria alternata is a common fungal species found globally. It thrives in diverse environments, both outdoors and indoors within human structures. This mold affects a broad range of plants as a pathogen and can trigger health issues in humans. Understanding its characteristics helps manage its impact.
Identification and Common Habitats
Alternaria alternata forms colonies that appear grayish-white, later turning olive-green to black on growth media. Visually distinguishing it from other common molds is challenging without specialized laboratory testing. Microscopic examination reveals characteristic dark brown conidiophores that produce asexual spores, known as conidia, responsible for its widespread dissemination.
Outdoors, this fungus thrives in moist, warm environments, common in humid climates or after rainfall. It commonly inhabits soil, decaying leaves, and compost piles. Spores of Alternaria alternata are airborne, facilitating its spread to seeds, seedlings, and various living plants.
Indoors, the mold seeks out damp or water-damaged areas, common in bathrooms, kitchens, and basements. It frequently colonizes window sills, areas with poor ventilation, and attics where moisture can accumulate. Elevated humidity or water intrusion, such as leaks, creates a conducive environment for its establishment and spread.
Health Implications for Humans
Alternaria alternata exposure causes allergic reactions in humans. It is a potent allergen, often triggering allergic rhinitis (hay fever) symptoms. Inhaling spores can cause sneezing, runny nose, and itchy eyes.
This mold contributes to asthma development and can provoke severe asthma attacks. Its spores contain allergenic proteins and proteases that interact with the respiratory system, potentially leading to inflammation, mucus overproduction, and airway hyperresponsiveness. Inhaling these components can exacerbate existing respiratory conditions and increase asthma risk.
Beyond common allergies, Alternaria alternata can cause less frequent but more serious health concerns. Repeated exposure can cause hypersensitivity pneumonitis, an allergic inflammation of the lung’s air sacs, with symptoms like a dry cough, shortness of breath, fatigue, and chest tightness. Rarely, immunocompromised individuals are susceptible to opportunistic infections, including alternariosis (skin or nail infections).
Impact on Plants and Agriculture
Alternaria alternata is a plant pathogen, infecting over 380 host species worldwide. It causes various diseases, including leaf spots, rots, and blights. Damage can be substantial, impacting plant health and agricultural yields.
It causes specific diseases in economically important crops. It causes stem canker in tomatoes, and leaf spot diseases in crops like potatoes, citrus fruits, and various grains. Date palms can suffer from inflorescence, leaf, shoot, and fruit rot.
Other affected plants include pomegranates (heart rot) and apples (leaf blotch, fruit spot). It also causes black spot in broccoli, fruit rot in kiwi, and leaf spots in gerbera, blackberry, fava beans. In some agricultural settings, such as mustard crops, it can reduce yields by up to 70%.
Managing Exposure and Infestations
Controlling moisture is primary for preventing and managing Alternaria alternata indoors. Maintain indoor humidity below 50% using dehumidifiers or air conditioners, especially during humid seasons. Promptly repair water leaks from plumbing, roofs, or windows to eliminate sources that encourage mold growth.
Improve ventilation in moisture-prone areas like bathrooms, kitchens, and laundry rooms to reduce humidity. Use exhaust fans and ensure adequate airflow in enclosed spaces like attics to prevent moisture buildup. For small mold growth on non-porous surfaces, cleaning with detergent and water is effective.
For extensive mold growth, professional mold remediation is advised. This includes infestations larger than 10 square feet or within the HVAC system. Professionals safely remove affected materials, clean air ducts, and verify remediation through post-cleanup testing.