Absidia

Definition & Etymology

Absidia is a genus of filamentous fungi in the order Mucorales. Many pathogenic species, such as Absidia corymbifera, are now reclassified into the genus Lichtheimia. These thermotolerant fungi are common in soil and decaying matter. They are characterized by rapidly growing, broad, and sparsely septate hyphae. Microscopically, their sporangiophores arise from stolons at internodal points (between rhizoids), supporting small, pear-shaped (pyriform) sporangia with a distinct, conical apophysis. This morphology differentiates them from related genera like Rhizopus.

Clinical Significance

Clinically, organisms of the Absidia complex are significant agents of mucormycosis, a highly aggressive opportunistic infection with high mortality. Infection typically occurs via spore inhalation. A key pathogenic feature is angioinvasion, where hyphae invade blood vessels, causing thrombosis and extensive tissue necrosis, which clinically presents as black eschars. The most common forms are rhinocerebral and pulmonary disease. Rapid diagnosis via biopsy, aggressive surgical debridement, and systemic antifungal therapy are critical for survival.

Related Conditions

Mucormycosis is almost exclusively a disease of immunocompromised hosts. The strongest risk factors are uncontrolled diabetes mellitus with diabetic ketoacidosis (DKA) and hematologic malignancies with severe neutropenia. Other susceptible populations include transplant recipients and patients on high-dose corticosteroid therapy. The disease can manifest as rhino-orbito-cerebral, pulmonary, cutaneous, or disseminated infection, all considered medical emergencies.

Key Takeaways

• Absidia is a genus of Mucorales fungi, with its primary pathogenic species now largely reclassified under Lichtheimia.
• It is a causative agent of mucormycosis, a rare but life-threatening opportunistic infection characterized by rapid angioinvasion and tissue necrosis.
• Infection predominantly affects severely immunocompromised individuals, especially those with diabetic ketoacidosis, neutropenia, or hematologic cancers.

Note: This content is for informational purposes only and does not substitute for professional medical advice. Always consult your doctor for diagnosis and treatment.