Cryptococcus neoformans

Cryptococcus neoformans

Cryptococcus neoformans is a major cause of meningoencephalitis in immunocompromised patients. It is widespread in the environment, particularly in soil mixed with bird droppings (especially pigeons) and in areas where eucalyptus trees are endemic. It causes opportunistic infections, typically transmitted through the inhalation of fungal spores, which settle and multiply in the alveoli, enter systemic circulation, and subsequently localize in the meninges.

Other common sites of cryptococcal infection include the lungs and, less frequently, the skin and soft tissues. The primary virulence factor is its thick polysaccharide capsule, mainly composed of glucuronoxylomannan (GXM).

In AIDS patients, it is a leading cause of morbidity and mortality. The majority of cryptococcal meningitis cases (72%) are reported in sub-Saharan Africa, where the mortality rate exceeds 80%. The diagnostic approach includes CSF general analysis, direct microscopy, special stains such as Indian ink and rapid immunoassays, including: Latex agglutination with polystyrene beads, which has a sensitivity of 97% and specificity of 86–100%, and reverse flow immunochromatography, with a sensitivity of 94% and specificity of 96%. Both immunoassays can be used on CSF and serum to detect the capsular polysaccharide antigen.

Culture on solid or liquid media remains the gold standard, followed by identification and antifungal susceptibility testing.

References

Rathore SS, Sathiyamoorthy J, Lalitha C, Ramakrishnan J. A holistic review on Cryptococcus neoformans. Microb Pathog. 2022 May;166:105521. doi: 10.1016/j.micpath.2022.105521. Epub 2022 Apr 15. PMID: 35436563.