The types of disease caused by fungi in humans can be divided into three categories: (1) respiratory allergies following sensitization due to inhalation of fungal antigens; (2) fungal intoxication due to ingestion of toxic substances such as amatatoxin and phallotoxin produced by certain poisonous mushrooms aflotoxins produced [Aspergillus] species which have been implicated in liver damage; (3) disease relating to specific infecting fungi.
More than 50 species of fungi cause disease in animals and man, forming two subsections: dermatophytoses, superficial infections of the skin, hair and nails; and mycoses, infections of the deeper tissues and organs. Dermatophytoses include ringworm and actinomycosis. Dermatophytoses are caused by fungi present on the surface of the skin; mycoses on the other hand live and grow independently of the host and infection is caused by inhaling or ingesting spores, or by the implantation of fungus under the skin through small punctures, cuts or bruises. Mycosis infections include [Coccidioidomycosis], [Histoplasmosis], [Cryptococcosis], and [Adiaspiromycosis]. Most of the fungi causing these diseases have been found in soil.
Mycoses are caused by a variety of fungi which attack diverse structures of the body, and are divided accordingly into three groups:< (1) Cutaneous, or superficial, mycoses attack the epidermis only, involving skin, hair or nails without invasion of the tissues. These are known clinically as Tinea infections; [Tinea capitis] is the well known scalp infection that occurs in childhood and heals spontaneouly in puberty. Superficial mycoses are most commomly caused by the so-called dermatophytes - [Microsporum] or [Tricophyton] spp. [eg] [Microsporum canis], [Microsporum gypsum] and [Trycophyton rubrum]. Their natural habitat is either man, animal or soil. Infection is due to direct contact of the skin with the infected surroundings.
(2) Subcutaneous, or intermediate, mycoses attack the epidermis, but they may also attack deeper structures. One of the most common offending species is [Candida albicans] producing a form of moniliasis; the yeast is part of the normal endogenous respiratory tract flora and may be present in the digestive tract as a saprophyte. Infection takes place by direct contact or by inhalation and spreads via the bloodstream.
(3) Deep mycoses attack deep structures in the body, but may metastatically also invade the epidermis. [Blastomyces], [Coccidioides] and [Histoplasma] are common fungal agents responsible for primary systemic disease; and each tend to occur in distinctive geographic locations, [Blastomyces dermatitidis] occurs mostly in North America (USA, Canada, and Mexico), [Coccidioidies immitis] mostly in the south-west USA and Latin America and [Histoplasma capsulatum] mostly in central USA.
Opportunistic fungi are mainly considered non-pathogenic but more and more often being found to cause disseminated infections in immuno-compromised and immunosuppressed individuals, or those weakened by a metabolic defect or who have undergone surgery. The infections caused may be subacute or chronic , some more like intermediate mycoses and some systemic. The diseases include aspergillosis, systemic candidosis and cryptococcosis. Exceptionally, other fungi that are normally not pathogenic, such as [Trichosporon], [Fusarium] or [Penicillium], may cause opportunistic systemic infections.