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Cryptococcosis is an infectious disease caused by Cryptococcus neoformans or Cryptococcus gattii; two encapsulated yeast species of the genus Cryptococcus.1 Although the organisms can infect healthy individuals, cryptococcosis is more common in immunocompromised indiviudals.2 The disease is usually associated with conditions such as acquired immunodeficiency syndrome (AIDS), diabetes, organ transplantation, malignancy, steroid or immunosuppressive therapy, defects in cell-mediated immunity, and chronic liver, kidney or lung diseases.2 The organisms can also cause meningitis, pneumonia and disseminated infections.1-3
DIAGNOSTIC TESTS Diagnosis of cryptococcosis relies on medical history, clinical symptoms, and laboratory tests.1-4 India ink examination is used to detect Cryptococcus in cerebrospinal fluid (CSF) for the diagnosis of cryptococcal meningitis. Since India ink cannot stain the yeast capsule surrounding the yeast cell, the ink can only stain the background and this results in a zone of clearance around the cells. Cryptococcus can be visualised as spherical cells with a halo against a dark background. False positive results can occur due to yeast cells being similar in appearance to lymphocytes and other tissue cells. 1-4 Culture helps isolate and identify Cryptococcus from specimens including CSF, blood, and sputum. Cryptococcus can grow within 48 to 72 hours at 20°C to 37°C on solid media (such as Blood Agar, Sabouraud Dextrose Agar and Bird Seed Agar). Colonies are usually creamy white in colour and turn yellow-tan to brown following a prolonged incubation period. The mucoid appearance of colonies indicates the capsule surrounding the yeast cell. However, most non-pathogenic Cryptococcus strains are unable to grow at these temperatures. Cerebrospinal fluid culture can be negative in cryptococcal
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immune reconstitution inflammatory syndrome (IRIS). This is a condition seen in individuals with AIDS, in which the recovery of the immune system after initiation of antiretroviral therapy responds to previously acquired opportunistic infections making clinical symptoms worse.1-4 Cytology is the microscopic examination of cells from centrifuged CSF sediment and other body fluids such as bronchoalveolar lavage. The sedimented CSF and other body fluids can be stained with periodic acid-Schiff (PAS) stain or mucicarmine stain which helps identify the yeast by labelling the capsule. This method is more sensitive than India ink staining.1-4 Histopathology involves the microscopic examination of tissues from the lung, skin and other organs. Specimens such as biopsies can also be stained with PAS stain or mucicarmine stain. In addition to PAS and mucicarmine stain, methenamine silver stain, which highlights the fungal cell wall, is a popular staining method to identify the yeasts in tissues.1-4 Serologic tests can detect polysaccharide capsular antigen of Cryptococcus in serum and CSF specimens. Serologic techniques that are commonly used for diagnostic purposes include latex agglutination test and lateral flow assay (LFA) 1-4. • Latex agglutination is widely utilised due to its high sensitivity and high specificity. False negative results, however, can occur due to low cryptococcal antigen concentrations. • Lateral flow assay also has high sensitivity and high specificity. Moreover, LFA has some advantages over other serologic techniques. Rapid turnaround time, low cost, no specimen preparation, and stability at room temperature means that LFA satisfies most of the criteria for a good point-ofcare test. For people with the Human Immunodeficiency Virus (HIV) who
are suspected to have cryptococcal meningitis, a rapid serological antigen assay (either latex agglutination or LFA) with rapid access to test results (less than 24 hours) is recommended as the preferred diagnostic approach.4 If rapid serological antigen assays are unavailable, CSF India ink examination is recommended as the preferred diagnostic test.4 When lumbar puncture is contraindicated, serum specimens can be used instead of CSF for serologic antigen assays.4
REFERENCES 1. Williamson P. R., Jarvis J. N., Panackal A. A., Fisher M. C., Molloy S. F., Loyse A., et al. Cryptococcal meningitis: epidemiology, immunology, diagnosis and therapy. Nature reviews Neurology. 2017;13(1):13-24. [Accessed 2019 Sep]. Available from: https://www.nature.com/articles/nrneurol.2016.167 2. Maziarz E. K., Perfect J. R. Cryptococcosis. Infectious disease clinics of North America. 2016;30(1):179-206. [Accessed 2019 Sep]. Available from: https://www.ncbi.nlm.nih. gov/pmc/articles/PMC5808417/ 3. Ruschel Marco A Pescador, Thapa Bicky. Meningitis, Cryptococcal. StatPearls [Internet]: StatPearls Publishing; 2018. [Accessed 2019 Sep]. Available from: https://www.ncbi. nlm.nih.gov/books/NBK525986/ 4. World Health Organization. Guidelines for the diagnosis, prevention and management of cryptococcal disease in HIV-infected adults, adolescents and children: supplement to the 2016 consolidated guidelines on the use of antiretroviral drugs for treating and preventing HIV infection Geneva 2018. [Accessed 2019 Sep]. Available from: https://apps.who.int/iris/bitstream/ handle/10665/260399/9789241550277eng.pdf;jsessionid=99443D4FCFF811D79239CE762318D5E8?sequence=1
