NAME: Cryptococcus neoformans
SYNONYM OR CROSS REFERENCE: C. neoformans var neoformans, C. neoformans var gattii (also known as C. gattii), cryptococcosis, cryptococcal infections, cryptococci, torulosis, European blastomycosis Footnote 1-Footnote 3 .
CHARACTERISTICS: C. neoformans is a spherical yeast, 4-6 µm in diameter, that produces a capsule containing glucoronoxylomannan (GXM), extending the overall diameter to 25 μm or more Footnote 4-Footnote 6. C. neoformans usually has a single bud that pinched off at the mature stage Footnote 4 . C. neoformans may also exist in pseudohyphal form. It is subgrouped into serotypes based on a defined set of capsule-reactive immune sera: A, B, C, D, and the hybrid A/D Footnote 2, Footnote 7. C. neoformans var neoformans contains serotypes A and D, and C. neoformans var. gattii contains serotypes B and C Footnote 1. C. neoformans can differentiate into several complicated morphological forms, including yeast, chlamydospores, pseudohyphae and hyphae, and is typically present in the yeast form during infections. Small-sized basidiospores (1.8 to 3.0 μm) can turn into yeast cells, the form preferred at 37°C, or can form dikaryotic hyphae which are favoured at 24°C Footnote 8. This organism exists as a yeast form in the environment Footnote 9.
PATHOGENICITY/TOXICITY: C. neoformans causes various diseases in immunocompromised and immunocompetent hosts Footnote 10. Diseases include meningoencephalitis (77.2%), pulmonary cryptococcosis (mostly in immunocompromised hosts, 8.2%), and several other diseases. Disseminated cryptococcosis is a complication and may occur in 91.8% of cases Footnote 11. Cryptococcosis may be fatal if untreated. Spores or desiccated yeast cells of C. neoformans enter the host respiratory tract by inhalation Footnote 1, Footnote 2. Serotypes A and D are opportunistic pathogens while serotypes B and C may infect immunocompetent individuals Footnote 1, Footnote 12. Pulmonary infection disseminates most commonly to the brain and the skin Footnote 2. C. neoformans can cause systemic infection, including fatal meningitis (meningoencephalitis) in normal, diabetic, and immunocompromised hosts Footnote 13. The infection from C. neoformans in the brain can be fatal if untreated Footnote 8.
CNS infection: Cryptococcosis of the CNS presents mostly in the form of acute, subacute, and chronic meningitis, with symptoms of persistent headache, nausea, dizziness, ataxia, impaired memory and judgment, irritability, somnolence, clumsiness, and confusion Footnote 6, Footnote 10. Patients may or may not have fever, and most have minimal or no nuchal rigidity. As the disease progresses, seizures may occur. CNS infection may also present as a brain abscess (cryptococcomas), subdural effusion, dementia, isolated cranial nerve lesion, spinal cord lesion, and ischaemic stroke. If cryptococal meningitis occurs, mortality rate is between 10-30% Footnote 14.
Respiratory infection: Pulmonary cryptococcosis may present as cough, dyspnea, blood-streaked sputum, and a dull ache in the chest Footnote 6. Other respiratory system infections include pneumonia, cavitation, endobronchial masses, empyema, nodules, sinusitis, mediastinitis, bronchiolitis obliterans, and pneumothorax Footnote 10.
Cutaneous infection: Skin lesions may be single or multiple and commonly begin as painless lesions of the face or scalp Footnote 6. Skin lesions may take the form of erythematous or umbilicated papules, pustules, acneiform lesions, indurated plaques, palpable purpura, soft subcutaneous masses, sinus tracts, cellulitis, vesicles, or large ulcers with undetermined edges.
Rarer presentations include lymphadenitis, pancreatitis, hepatitis, peritonitis, oesophagitis, osteomyelitis, septic arthritis, myositis, endophthalmitis, papilloedema, optic nerve atrophy, pyelonephritis, prostatitis, endocarditis, fungaemia, myocarditis, pericaditis, Cushing’s syndrome, adrenal insufficiency, adrenal mass lesions, and thyroiditis Footnote 10 .
EPIDEMIOLOGY: There are differences in number of cases in different strains of C. neoformans Footnote 1. C. neoformans serotypes A and D are distributed worldwide and cause the vast majority of cryptococcal infections, predominately in immunocompromised individuals. Serotype A is responsible for over 95% of cryptococcosis cases worldwide Footnote 1. C. neoformans serotype A appears to be implicated in 99% of AIDS patients with cryptococcosis worldwide, except in France where serotype A is responsible for around 80% of the infections Footnote 12. More frequent cases of serotype A and D have been reported in Europe where cryptococcosis is associated with 77% of HIV patients. C. gattii strains B and C are localized in tropical and subtropical regions (e.g. Australia, Papua New Guinea, and South America) and cause cryptococcal infections mostly in immunocompetent hosts Footnote 1. C. gattii isolates can also cause infections in regions with a temperate climate. Cryptococcal meningitis, caused by the fungus C. neoformans, can cause up to 30% mortality in AIDS patients in resource-poor regions such as Southeast Asia Footnote 1. It is estimated that 6% to 10% of patients with AIDS in the United States, Western Europe, and Australia and 0% to 50% of AIDS patients in sub-Saharan Africa are infected with life-threatening cryptococcal meningitis Footnote 12. By the 1990s, C. neoformans had become the leading cause of culture-positive meningitis in many regions, including New York City. Cryptococcal meningitis alone kills about 624,000 people each year Footnote 1.
INFECTIOUS DOSE: Unknown.
INCUBATION PERIOD: Unknown, C. neoformans can colonize in the host respiratory tract for months to years without causing any clinical symptoms Footnote 1.
COMMUNICABILITY: Person-to-person transmission has not been documented other than through transplanted organs Footnote 6.
RESERVOIR: C. neoformans may be found in humans and various domestic and wild animals Footnote 1, Footnote 7. Soil and decaying vegetation is also a reservoir for serotypes A and D Footnote 1, while serotypes B and C are found in trees. C. neoformans is associated with various environmental niches, especially avian guano Footnote 1, Footnote 9.
ZOONOSIS: Although C. neoformans may be encountered in animals, direct transmission from animals to persons has not been proven Footnote 17.
DRUG SUSCEPTIBILITY/RESISTANCE: Amphotericin B or itraconazole Footnote 15 with or without flucytosine or flucanazole.
DRUG RESISTANCE: C. neoformans can develop resistance to fluocytosine when used alone Footnote 5.
SUCEPTIBILITY TO DISINFECTANTS: C. neoformans is effectively killed by 70% ethyl alcohol and is susceptible to phenolic compounds, formaldehyde, glutaraldehyde, iodophors, and sodium hypochloride (1%) Footnote 18, Footnote 19.
PHYSICAL INACTIVATION: Photodynamic therapy (PDT), which combines methylene blue (MB) with a low-power red laser can inactivate C. neoformans Footnote 20. PDT can be performed using 150 μM MB and 100mW red laser with a florescence at 180J/cm2 for 9 min. C. neoformans can be inactivated by UV, microwave, gamma radiation, moist heat (121°C for at least 20 min), and dry heat (165-170°C for 2 h) Footnote 21-Footnote 24.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID TREATMENT: Give appropriate antifungal therapy Footnote 6.
IMMUNIZATION: No immunization is currently available Footnote 15; however, some vaccines are currently in clinical trials, including GXM conjugated to tetanus toxoid vaccine, which has been shown to be effective in immunocompetent individuals in clinical trials Footnote 12.
PROPHYLAXIS: HIV patients may receive antifungal therapy such as fluconazole when no symptoms of infections are present Footnote 9.
LABORATORY ACQUIRED INFECTIONS: There is 1 reported case of laboratory exposure to C. neoformans from a laceration by a contaminated scalpel blade Footnote 26. There are 2 reported cases of eye infections related to surgical procedure from C. neoformans Footnote 9. Cryptococcosis from a needle puncture to the thumb during blood collection from an AIDS patient with cryptococcal fungemia and two percutaneous cryptococcal inoculations from needlestick have been reported.
SOURCES/SPECIMENS: C. neoformans may be found in soil, bird guano, blood, urine, and specimens from bone marrow, brain, CSF, eye, respiratory sites, skin, and mucous membranes Footnote 1, Footnote 4, Footnote 26.
PRIMARY HAZARD: Inhalation of basidiospores and desiccated yeast cells could be infectious for the lab workers and should be regarded as potentially serious airborne hazards Footnote 9. Accidental parenteral inoculation of infectious materials may also occur Footnote 9, Footnote 26.
SPECIAL HAZARD: Bites from infected lab mice and manipulation of infectious environmental materials (e.g. pigeon dropping) may be a potential hazard Footnote 26.
RISK GROUP CLASSIFICATION: Risk Group 2 Footnote 27.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures Footnote 28.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 28.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities Footnote 28.
SPILLS: Allow aerosols to settle. Wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at perimeter and working towards the centre; allow sufficient contact time before clean up.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism by autoclave, chemical disinfection, gamma irradiation, or incineration before disposing.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: October 2010
PREPARED BY: Pathogen regulation directorate, Public Health Agency of Canada
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2010