neoformans

Cryptococcus neoformans is a species of encapsulated yeast that is an important human pathogen. It belongs to the genus Cryptococcus within the basidiomycete fungi. The organism has a thick polysaccharide capsule; colonies on fungal media are typically mucoid, and the capsule can be demonstrated by India ink staining.

It is found worldwide in soil, decaying wood, and especially in association with bird droppings, notably pigeons. Humans acquire infection by inhaling airborne particles. Most exposures are subclinical or cause mild pulmonary disease, but in certain individuals the fungus can disseminate to the central nervous system.

Cryptococcal disease most often involves the lungs and central nervous system. Cryptococcal meningitis presents with subacute headaches, fever, nausea, neck stiffness, and altered mental status; raised intracranial pressure is common. Other sites include skin, bones, and disseminated infection.

Diagnosis relies on detection of cryptococcal antigen in serum or CSF (latex agglutination or lateral flow assay), which is highly sensitive. CSF analysis with India ink staining, fungal culture on Sabouraud dextrose agar, and imaging support the diagnosis. CSF findings in meningitis typically show elevated opening pressure, low glucose, and lymphocytic pleocytosis.

Treatment begins with induction therapy using liposomal amphotericin B plus flucytosine for at least two weeks, followed by consolidation with fluconazole and a maintenance phase lasting 6–12 months, depending on immune status and CSF sterilization. In HIV-infected patients, antiretroviral therapy should be optimized when feasible, and intracranial pressure should be managed with therapeutic lumbar punctures.

C. neoformans is distinguished from Cryptococcus gattii, which more often infects immunocompetent hosts in certain geographic niches. No vaccine is currently available, and prevention focuses on reducing exposure in high-risk individuals.