Invasive Fungal Infections of the Central Nervous System in Immune-Competent Hosts

Abstract

Fungal infections of the central nervous system (CNS) occur more commonly in immunosuppressed individuals. However, they are being recognized in apparently immune-competent hosts in recent times. Understanding the risk factors, characters of the fungus, and pathogenesis is important. Fungal infections of CNS in apparently immune-competent hosts are described following neurosurgical procedures, head trauma, patients exposed to contaminated devices/drugs, or natural disasters. Disruption of the meninges and blood-brain barrier and direct inoculation of the fungal spores into the subarachnoid space are implicated in the pathogenesis. Contamination of drugs used for epidural injections resulted in an epidemic of fungal meningitis by a dematiaceous fungus, which was never reported earlier to cause CNS disease. Certain fungi like Coccidioides, Paracoccidioides, Histoplasma, and Blastomyces are endemic and the high concentrations in the environment and exposure are risk factors for invasive infections. Heavy and constant exposure in hot and humid climate is responsible for Aspergillus flavus infections in tropical countries. Some fungi such as Cryptococcus spp. and dematiaceous fungi are neurotropic. Environmental, genetic, and socioeconomic factors are also implicated. The exact pathogenesis remains unclear. The intense inflammatory response elicited by immune-competent hosts is likely to result in host damage. Sub-optimal health care facilities in developing countries along with environmental and climatic changes likely result in invasive infections in immune-competent hosts. Awareness of invasive fungal infections in immune-competent host with uncommon clinical presentation and uncommon etiological agents is important for early diagnosis.