Fungal Mycosis and Protozoans

Fungal Mycosis

• Mycosis refers to fungal diseases. The classification of these infections depends on their location in the body.

Types of Fungal Infections

• Cutaneous (Superficial): Confined to the outermost layers of skin, hair, and nails.

  • These fungi need keratin to grow.

• Intermediate (Subcutaneous): Start as cutaneous infections and penetrate into lower skin layers or muscles.

  • They usually don't spread throughout the entire body.

• Deep Seated (Systemic): Affect multiple organ systems, commonly starting in the respiratory system due to spore inhalation.

Dimorphic Fungi

• Many fungi causing human diseases are dimorphic, meaning they have two forms.

  • In the soil, they typically grow as molds (fuzzy, cottony growths).

  • In the body, they appear as yeasts.

Cutaneous Mycosis

• As stated previously, these infections are limited to the outer layers of skin, hair, and nails and require keratin for growth.

• Generally, they are non-invasive, with symptoms caused by the presence and metabolic products of the organism, which can cause skin irritation.

• Can be caused by molds or yeasts.

Cutaneous Mycosis Caused by Molds (Dermatophytes)

• Dermatophytes include three genera: Microsporum, Epidermophyton, and Trichophyton.

• A dermatophyte infection requires the presence of two or three different genera.

  • For example, multiple species from the same genus (e.g., two Microsporum species) would not cause dermatophytosis.

• They produce Arthrospores.

• Cause ringworm infections, named with the term "tinea" followed by the location of the infection.

  • Tinea is Latin for ringworm but is not a scientific name.

• Ringworm presents as a circular pattern with a raised edge due to the immune response to the fungus, not a worm.

Examples of Ringworm Infections

• Tinea Corporis: Ringworm on any part of the body.

• Tinea Pedis: Ringworm of the feet (athlete's foot), often between the toes, which can spread to the arch or nails.

• Tinea Unguium (Onychomycosis): Ringworm of the nail, usually due to undertreated athlete's foot.

  • Risk can be increased by unsanitized salon instruments. Sterilization commonly involves washing instruments followed by placement in a UV light box.

• Tinea Capitis: Ringworm of the scalp, mainly seen in children and babies, and is often confused with cradle cap (normal exfoliation of skin cells).

• Tinea Cruris: Historically known as jock itch, now seen in both genders, associated with constrictive clothing, causing a favorable environment for fungal growth.

  • Fungi thrive in salty, warm, dark, and moist conditions.

• Tinea Barbae: Ringworm in shaved areas (beard, groin, legs, underarms), as shaving can cause micro-abrasions, making the skin more susceptible.

  • Barbershop combs are often soaked in an antifungal solution (e.g., Barbasol) to prevent spread.

Cutaneous Infections Caused by Yeasts

• Candida Albicans: Causes candidiasis, or yeast infections on the skin, and thrush (oral yeast infection).

  • It is a part of normal flora but is kept in check by other microorganisms.

  • Overgrowth is often due to compromised immunity.

• Symptoms include inflammation, redness, itching, and a white, creamy appearance.

  • Candida metabolizes sugars, leaving behind byproducts that make skin feel clammy.

• Can affect both humans and animals.

  • Antibiotic use can lead to yeast infections.

• Thrush is a less common, but more serious because this can be a sign of a compromised immune system in adults.

Subcutaneous Mycosis

• Often start as cutaneous infections and move into deeper skin layers or muscles and are typically caused by soil organisms introduced through wounds which may include cuts, scratches, scrapes, or thorn pricks.

Sporotrichosis (Rosepicker's Disease)

• Caused by Sporothrix.

• Has an incubation period of one to twelve weeks.

• Begins as a small, painless bump at the entry site, which can be red, pink, or dark.

• Commonly found on fingers, hands, or arms of people who work outdoors.

• The bump enlarges and opens, forming a non-scabbing sore that heals slowly (self-limiting). Very few individuals will find it goes onto something more serious.

Deep Seated (Systemic) Mycosis

• Affect one or more body systems, commonly acquired through inhalation of spores.

• Start as pulmonary infections but can spread and become life-threatening.

• Most are dimorphic (mold in soil, yeast in body).

• Diseases are endemic to specific areas due to climate.

Mold Mycosis

Histoplasmosis (Spelunker's Disease)

• Caused by Histoplasma capsulatum, which has a protective coating.

• Found in the Mississippi and Ohio River Valleys.

• Grows as a mold in moist soils contaminated with bat or bird droppings (primarily bats in this region) and as a yeast within human macrophages, impairing their function.

• Most common pulmonary mycosis in humans.

• Associated with caves where bats nest.

• Spores are aerosolized from bat waste and inhaled.

• Symptoms include a lingering productive cough.

• Treated with antifungal agents that have more side effects than antibiotics since both fungi and humans are eukaryotes.

Coccidioidomycosis (Cactus Cough or Valley Fever)

• Caused by Coccidioides immitis.

• Found in dry, desert-type (arid) climates.

• Grows as a mold in soil and a spherule in tissues.

• Causes coughing possibly that includes fluid accumulation.

• Mold growth requires some moisture in the soil, often following monsoon season.

• Spores are released into the air when the soil dries and can be inhaled by people.

North American Blastomycosis

• Caused by Blastomyces dermatitidis.

• Originally identified as a veterinary pathogen.

• Dimorphic, growing as a mold and a yeast.

• First seen in Wisconsin in herding dogs as open, ulcerated wounds.

• Begins as a cutaneous or pulmonary infection, then spreads.

• In humans, presents as a systemic disease or respiratory tract infection.

• In animals, can invade other tissues.

• Infection site determines symptoms and damage.

  • If in the eyes, it causes permanent blindness.

  • If in the brain it causes lesions.

  • If in bones, it causes loss of bone mass (Swiss cheese appearance), weakening the bones.

• Human cases require aggressive treatment, often including eye removal or limb amputation.

• Common in moist, acidic soil near fresh water.

Yeast Mycosis

Cryptococcosis

• Disease caused by a yeast, specifically Cryptococcus neoformans.

  • Neo means new, formans means shape.

• Heavily encapsulated and found globally.

• Associated with bird droppings.

• Infection starts in the lungs (pulmonary disease) but can spread to the central nervous system, skin, bones, and organs.

• Common in immunocompromised, immunosuppressed, or immunodeficient individuals.

• Can cause meningitis, which is a common disease among AIDS patients.

• Immunocompetent people typically eliminate the fungus before it causes disease.