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Alternaria Species

The U.S. Government’s Occupational Safety and Health Administration [OSHA] lists the following as the health effects of Alternaria mold: Allergen, Irritant, Hypersensitivity Pneumonitis, Dermatitis.

Taxonomic Classifications

Kingdom: Fungi
Phylum: Ascomycota
Class: Euascomycetes
Order: Pleosporales
Family: Pleosporaceae
Genus: Alternaria

brown hyphae and conidia
mature conidia have transverse and longitudinal divisions septate hyphae charts_fungi/fungi/alternaria.html


The dark brown spores are borne in simple or branched chains from the tips of simple dark conidiophores and are divided into several cells by transverse and vertical walls. New spores are produced by the extrusion of wall material through a pore at the tip of the previous spore. Commonly isolated from decaying plant materials; also causing plant diseases. Spores of Alternaria species are dispersed by air currents and are usually a major component of outdoor air. Holomorphs: Clathrospora, Leptosphaeria, Pleospora, Pyrenophora. Refs: Ellis 1971, 1976; Joly 1964.

Above mold photos and captions are courtesy of: Malloch/Moulds/Alternaria.html
For more alternaria mold photos, please visit or click on:
Alternaria Mold Picture.

Description and Natural Habitats

Alternaria is a cosmopolitan dematiaceous (phaeoid) fungus commonly isolated from plants, soil, food, and indoor air environment. The production of melanin-like pigment is one of its major characteristics. Its teleomorphic genera are called Clathrospora and Leptosphaeria.

The large spore size 20 - 200 microns in length and 7 - 18 microns in sizes, suggests that the spores from this fungi will deposited in the nose, mouth and upper respiratory tract.

Specimens of Alternaria are often found growing on carpets, textiles and horizontal surfaces such as window frames. It is commonly found in soil, seeds and plants. It is known to be a common allergen. It appears as a velvety tuft with long soft hairs and its color ranges from dark olive green to brown. Alternaria is a dry spore and is readily found in air samples as well as on tape lift samples. Alternaria is commonly found in water damaged buildings, and a significant increase in its numbers compared to outdoor levels can be a sign of growth.

Commonly found in outdoor air, on many kinds of plants and food products and prefers rotting farmland manure.  It may be resistant to fungicides. Alternaria is considered an occasional contaminant of water damaged building materials which contain cellulose.  Although Alternaria is a notable source of fungal allergy, pathogenic infections are also reported infrequently.


The genus Alternaria currently contains around 50 species. Among these, Alternaria alternata is the most common one isolated from human infections. Some authorities suggest that Alternaria alternata is a representative species complex rather than a single species and consists of several heterogenous species. While Alternaria chartarum, Alternaria dianthicola, Alternaria geophilia, Alternaria infectoria, Alternaria stemphyloides, and Alternaria teunissima are among the other Alternaria spp. isolated from infections, some Alternaria strains reported as causative agents remain unspecified.

Health Effects

Among the species of alternaria, the species Alternaria alternata is capable of producing tenuazonic acid and other toxic metabolites which may be associated with disease in humans or animals. Alternaria produces large spores having sizes between 20 - 200 microns in length and 7 - 18 microns in width, suggesing that the spores from this fungi are deposited in the nose, mouth, and upper respiratory tract. It may be related to bakers asthma. It has been associated with hypersensitivity pneumonitis, sinusitis, deratomycosis, onychomycosis, subcutaneous phaeohyphomycosis, and invasive infection. Common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms include edema and bronchiospasms, chronic cases may develop pulmonary emphysema. Further explanations about the health disease caused by alternaria species shown below:

1. onychomycosis -  Fungal Infection of the nails is known as "onychomycosis". It is increasingly common with increased age. It rarely affects children.

Lateral onychomycosis

Source of above photo and caption :

2. subcutaneous phaeohyphomycosis
- Subcutaneous infections occur worldwide, usually following the traumatic implantation of fungal elements from contaminated soil, thorns or wood splinters. Exophiala jeanselmei and Wangiella dermatitidisare the most common agents and cystic lesions occur most often in adults. Occasionally, overlying verrucous lesions are formed, especially in the immunosuppressed patient.


Subcutaneous phaeohyphomycosis
caused by
Exophiala jeanselmei

Subcutaneous phaeohyphomycosis
caused by Wangiella dermatitidis.

Source of above photos and   caption:

Macroscopic Features

Alternaria spp. grow rapidly and the colony size reaches a diameter of 3 to 9 cm following incubation at 25°C for 7 days on potato glucose agar. The colony is flat, downy to woolly and is covered by grayish, short, aerial hyphae in time. The surface is greyish white at the beginning which later darkens and becomes greenish black or olive brown with a light border. The reverse side is typically brown to black due to pigment production.

Microscopic Features

Alternaria spp. have septate, brown hyphae. Conidiophores are also septate and brown in color, occasionally producing a zigzag appearance. They bear simple or branched large conidia (7-10 x 23-34 µm) which have both transverse and longitudinal septations. These conidia may be observed singly or in acropetal chains and may produce germ tubes. They are ovoid to obclavate, darkly pigmented, muriform, smooth or roughened. The end of the conidium nearest the conidiophore is round while it tapers towards the apex. This gives the typical beak or club-like appearance of the conidia

Laboratory Precautions

No special precautions other than general laboratory precautions are required.


In vitro susceptibility testing for phaeoid fungi is not standardized yet. The in vitro activity of some novel antifungal drugs has so far been investigated. While caspofungin was shown to be active in vitro against Alternaria, voriconazole also appeared promising and generated lower MICs than itraconazole for Alternaria strains .

Amphotericin B and flucytosine therapy may achieve successful clinical outcome in phaehyphomycosis. Treatment with fluconazole, itraconazole, or terbinafine may also be effective. However, further data are required to clarify their actual place in treatment of Alternaria infections.

The mycological information gathered and organized in this extensive research on the different Pathogenic Molds was  sourced out from the list of websites below: | | | | | | | | | | | | | | | 

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