Aspergillus

Aspergillus fumigatus is the most common pathogenic species. Key morphologic feature: septate hyphae that branch at acute (45-degree) angles, distinguishing it from Mucor/Rhizopus (broad, non-septate, right-angle branching). Clinical syndromes: (1) Allergic bronchopulmonary aspergillosis (ABPA) - hypersensitivity reaction in asthma/cystic fibrosis patients, presents with recurrent bronchial obstruction, eosinophilia, elevated IgE, and central bronchiectasis; treated with corticosteroids +/- itraconazole. (2) Aspergilloma ('fungus ball') - colonizes pre-existing lung cavities (e.g., from prior TB), can cause hemoptysis; visible as a mobile mass within a cavity on imaging. (3) Invasive aspergillosis - occurs in neutropenic or immunosuppressed patients (e.g., post-transplant, prolonged steroid use, hematologic malignancy); can cause pneumonia with angioinvasion leading to hemorrhagic infarction, and can disseminate to brain, sinuses. Classic CT finding: 'halo sign' (early) or 'air-crescent sign' (recovery phase). Diagnosis: galactomannan antigen test (serum/BAL), beta-D-glucan (nonspecific for fungi), culture, and biopsy showing septate hyphae with acute-angle branching. Treatment: voriconazole is first-line for invasive disease; amphotericin B as alternative. Aspergillus also produces aflatoxins (from A. flavus) which are hepatocarcinogens associated with hepatocellular carcinoma, especially with contaminated grains/peanuts and synergistic with HBV infection.