Alternaria
General Structure and Shape:
Spores of Alternaria can be formed singly, but most often in chains. They are typically club-shaped and are highly septate, having divisions in both vertical and horizontal directions. The spore surfaces are usually smooth, but may have small rounded warts creating a slightly rough surface. A beak of varying length is distinctive for this genus.
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Atmospheric Prevalence:
The concentration of Alternaria spores in the air generally peaks during the summer and early fall seasons of the year in temperate areas. Next to Cladosporium, Alternaria represents one of the most prevalent contributors to the dry air spora in the atmosphere.
Allergenic Activity:
The spores are known to be prevalent sources of allergens in the atmosphere, generally causing symptoms associated with respiratory problems. Such symptoms include allergic rhinitis (hay fever), asthma, and hypersensitivity pneumonitis. Several studies have shown associations between Alternaria and severe asthma.
Viability:
Alternaria species are known to be resistant to changes in the amount of water available, as they have been observed to resume growth after extended periods of drying.