Mycology Fungal Diseases in Humans

Superficial

Limited to outermost layers of skin and hair causing little inflammation

Examples of superficial human fungal infections

Pitryiasis versicolor (Malassezia spp.), White piedra (Trichosporon spp.)

Cutaneous

Extend deeper into epidermis, and include invasive hair and nail diseases

Examples of cutaneous human fungal infections

Athlete’s foot (dermatophytes including Trichophyton spp.)

Subcutaneous

Involve dermis, subcutaneous tissues, muscle, and fascia

Examples of subcutaneous human fungal infections

Sporotrichosis (Sporothrix)

Systemic/invasive

Originate primarily in lungs and may spread to many organ systems

Examples of systemic/invasive human fungal infections

Aspergillus, Cryptococcus, Mucorales

The infection cycle

Infectious agent -> reservoir -> portal of exit -> mode of transmission -> portal of entry -> susceptible host ->

What is an infectious agent?

Fungi

What is the reservoir?

Environment (soil), animals, other humans

What is portal of exit?

Spore dispersal, faeces

What are the modes of transmission?

Airborne, direct contact, inoculation

What are the portal's of entry?

Respiratory, skin, mucous membranes

What is the susceptible host?

Immune deficiency, age, underlying disease, damaged skin, IV lines

Pathogenicity mechanisms

1) direct invasion- leads to distortion and tissue destruction

2) obstruction - leads to bacterial infection

3) angioinvasion - leads to thrombosis

4) embolism to distal vessels

5) intracellular persistance and even multiplication in macrophages and neutrophils

6) capsule formation-protects fungus and may damage tissue