11.2 Deep-seated and systemic mycoses

What are systemic (deep-seated) mycoses?

Fungal infections that affect internal organs such as lungs, blood, CNS, and other tissues.

What is the most common mode of transmission for systemic fungi?

Inhalation of fungal spores from the environment.

Who is most at risk for systemic fungal infections?

Immunocompromised individuals (AIDS, transplant patients, chemotherapy, corticosteroid therapy).

What are the microscopic forms of Candida?

Yeast cells, pseudohyphae, and true hyphae.

What test is commonly used to confirm Candida albicans?

Germ tube test.

Where does Candida normally reside in the body?

Normal microbiota of the gastrointestinal and genitourinary tracts.

What is the most clinically important species of Cryptococcus?

Cryptococcus neoformans.

What is the main environmental reservoir of Cryptococcus neoformans?

Bird droppings, especially pigeon droppings.

How is Cryptococcus transmitted to humans?

Inhalation of spores.

What is the most common severe disease caused by Cryptococcus?

Meningoencephalitis.

What major virulence factor does Cryptococcus neoformans possess?

Polysaccharide capsule.

Functions of the Cryptococcus capsule?

• Antiphagocytic

• Inhibits leukocyte migration

• Dysregulates cytokines

• Causes brain oedema

Another virulence factor of Cryptococcus besides capsule?

Melanin production.

What stain is used to visualize the capsule of Cryptococcus?

India Ink stain.

What rapid test detects Cryptococcus capsule antigen?

Latex agglutination test.

Treatment for severe cryptococcosis (e.g., meningitis)?

Amphotericin B ± flucytosine.

Where is Aspergillus commonly found?

Soil, plants, grains, and decomposing organic matter.

How is Aspergillus transmitted?

Inhalation of airborne conidia.

Common pathogenic Aspergillus species?

• A. fumigatus

• A. flavus

• A. niger

• A. terreus

What is an Aspergilloma?

A fungal ball colonising pre-existing lung cavities.

Who is at risk for invasive Aspergillosis?

Immunocompromised patients (neutropenia, transplant, chemotherapy).

What stain is used for histological detection of Aspergillus?

Grocott’s Methenamine Silver (GMS) stain.

Key microscopic feature of Aspergillus?

Septate hyphae with dichotomous branching.

First-line treatment for invasive Aspergillosis?

Voriconazole or Amphotericin B.

What are dimorphic fungi?

Fungi that grow as mould at 25°C and yeast at 37°C.

Examples of dimorphic fungal pathogens?

• Blastomyces dermatitidis

• Coccidioides immitis

• Histoplasma capsulatum

• Paracoccidioides brasiliensis

What organism causes Blastomycosis?

Blastomyces dermatitidis.

Key microscopic feature of Blastomyces yeast?

Broad-based budding yeast cells.

How is Blastomycosis transmitted?

Inhalation of conidia from soil.

What disease is caused by Coccidioides immitis?

Valley fever.

Characteristic tissue form of Coccidioides?

Spherules containing endospores.

Natural reservoir of Coccidioides?

Soil in arid regions.

What organism causes Histoplasmosis?

Histoplasma capsulatum.

Environmental reservoir of Histoplasma?

Soil contaminated with bat or bird droppings.

Typical microscopic feature of Histoplasma in tissue?

Small intracellular budding yeast in macrophages.

What organism causes Paracoccidioidomycosis?

Paracoccidioides brasiliensis.

Classic microscopic appearance of Paracoccidioides?

Multiple budding yeast resembling a “steering wheel.”

Most common cause of zygomycosis?

Rhizopus oryzae.

Who is at highest risk for rhinocerebral zygomycosis?

Patients with uncontrolled diabetes mellitus.

Pathogenesis of zygomycosis?

Fungi invade blood vessels causing thrombosis and tissue necrosis.

Common clinical form of zygomycosis?

Rhinocerebral infection.

Treatment for zygomycosis?

Amphotericin B + surgical debridement.