Which of the following is considered a classical opportunistic fungus?
a. Blastomyces
b. Histoplasma
c. Fonsecaea
d. Aspergillus

Verified step by step guidance

1. Step 1: Understand the term 'classical opportunistic fungus' — these fungi typically cause infections primarily in immunocompromised individuals, taking advantage of weakened host defenses.
2. Step 2: Review each option's general characteristics and typical clinical presentations: Blastomyces and Histoplasma are dimorphic fungi known for causing systemic infections in healthy hosts, not primarily opportunistic.
3. Step 3: Consider Fonsecaea, which is associated with chromoblastomycosis, a chronic cutaneous infection, but it is not classically categorized as an opportunistic pathogen.
4. Step 4: Recognize Aspergillus as a mold that commonly causes opportunistic infections, especially in immunocompromised patients, such as invasive aspergillosis.
5. Step 5: Conclude that among the options, Aspergillus fits the definition of a classical opportunistic fungus due to its clinical behavior and epidemiology.

Key Concepts

Opportunistic Fungi

Opportunistic fungi are organisms that normally do not cause disease in healthy individuals but can cause infections in immunocompromised hosts. These fungi exploit weakened immune defenses, leading to infections that are often severe and difficult to treat.

Classical Opportunistic Fungi Examples

Classical opportunistic fungi include species like Aspergillus, Candida, and Cryptococcus. These fungi are well-known for causing infections primarily in patients with compromised immune systems, such as those with HIV/AIDS, cancer, or undergoing immunosuppressive therapy.

Distinction Between Primary Pathogens and Opportunistic Fungi

Primary fungal pathogens, such as Blastomyces and Histoplasma, can cause disease in healthy individuals by overcoming normal immune defenses. In contrast, opportunistic fungi like Aspergillus cause disease mainly when the host's immunity is impaired.