Cryptococcosis
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Cryptococcosis also called as Torulosis is a subacute or chronic fungal infection caused by Cryptococcus neoformans. It leads to compications such as fatal meningoencephalitis. It is an opportunistic infection in HIV-infected patients. The PPT discuss on the morphology of the fungus, pathogenesis, laboratory diagnosis and treatment.
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Cryptococcosis
- 2. Def: cryptococcoccosis is a subacute or chronic infection caused by yeast Cryptococcus neofomans. Also called Torulosis Produces potentially fatal meningoencephalitis in HIV patients. Causative agents Two species: C. neoformans and C. gattii. Four serotypes: A, B, C and D.
- 3. 1. Cryptococcus neoformans It is a round or ovoid budding cell Size: 4-20 µm in diameter. It’s a true yeast Due to prominent polysaccharide capsule. Varieties of C. neoformans a. C. neoformans var. grubii b. C. neoformans var. neoformans 2. Cryptococcus gattii – is antigenically diverse - corresponds to serotypes A and D.
- 4. Other species: C. albidus and C. laurentii. Other agents of cryptococcosis: Teleomorphs for fungus -belong to Basidiomycetes: Filobasidiella neoformans and F. basiliospora.
- 5. pathogenesis Source: birds’ excretions. Route: Infection is acquired by inhalation of aerosol forms of Cryptococcus through lungs. Leads to pulmonary infection. Other way: through skin or mucosa. Both yeast cells and basidiospores (sexual stage of Cryptococcus) are infectious. In immunocompetent individuals: lungs have defence mechanisms which limit the infection. In people with low immunity: pulmonary infection occurs followed by dissemination through blood.
- 7. CNS spread Cryptococcus has ability to cross the blood-brain barriers. The cells migrate directly across endothelium or carried inside macrophages as ‘Trojan horse’. Present as discrete nodules- Cryptococcoma. Virulence factors Polysaccharide capsule: -is anti-phagocytic. - inhibits hosts local immune responses. Ability to make melanin: - produces an enzyme (phenyl oxidase) - it breaks down caffeic acid to melanin Other enzymes: ex, phospholipase and urease.
- 8. Risk factors Patients with advanced HIV infection. -they have less CD4 T cell counts [<200/µl] -they are at high risk. Patients with haematological malignancies. Transplant recipients. Patients on immunosuppressive or steroid therapy. Old buildings- exposure to spores.
- 9. Clinical manifestations 1. Pulmonary Cryptococcosis: - Respiratory tract: most common entry. - Seen in immunocompetent host. - Patient develops asymptomatic or mildly pneumonitis. - Results in an encapsulated lung nodule: Cryptococcoma. - Symptoms: chronic cough, low grade fever, chest pain, scant mucoid or blood- tinged sputum, malaise (disconfortness) and weight loss
- 10. 2. Disseminated infections May lead to visceral, cutaneous, meningoencephalitis disease or ocular cryptococcosis. A. CNS Cryptococcus/ Cryptococcus meningoencephalitis Present as chronic meningitis C. neoformans var. neoformans and C. gattii are strongly neurotropic -they disseminate from primary pulmonary site to the CNS. - Infection may extend to brain: forms massive lesions or mucoid cysts. - Leads to cryptococcal meningoencephalitis/meningitis. - they invade the leptomeninges. Signs & symptoms: headache, fever, meningismus, loss of vision, sensory & memory loss, and seizures. - Cryptococcal infection mimic tuberculosis and other chronic types of meningitis. - seen in AIDS patients.
- 11. B. Visceral Cryptococcus/osseous cryptococcosis: -simulate tuberculosis and cancer. -leads to osteolytic of bones (osteomyelitis). -uncommon but severe infection. -infection acquired by haematogenous spread from a self-limited pulmonary or lymph node localization, or -originates from contiguous skin lesion.
- 12. C. Cutaneous Cryptococcus -Results from haematogenous dissemination of infection or -Primary cutaneous lesion- following inoculation of the fungus into skin. - Lesions may be papules, acneform pustules or subcutaneous abscesses- may ulcerate. - Ulcers may multiply and resemble carcinoma. - Commonly caused by neoformans species.
- 13. D. Ocular Cryptococcal Patients develop keratitis, papilledema, scotoma, chorioretinitis and ocular palsy Leads to visual loss
- 14. Laboratory diagnosis Specimen collection -specimens: Sputum, CSF, Blood, skin scrapings. 1. Microscopy Negative staining: India Ink and Nigrosin stain -modified India ink with added 2% mercurochrome is used -demonstrates capsule: appears as refractile delineated clear space around the cells. -drawback: India ink is less sensitive (60-70%). KOH Preparation: used for sputum Gram stain: reveals Gram- positive, budding yeast cells. - surrounded by a halo or clear area- reveals capsule.
- 16. Other stains Mucicarmine stain: stains carminophilic cell wall of C. neoformans. Masson- fontana stain: demonstrates production of melanin. Alacin blue stain: demonstrates capsule.
- 17. 2. culture Specimen: inoculated on SDA. Plates are incubated at 37°C. Blood: inoculated in biphasic blood culture bottles. Colonies: mucoid creamy white colonies -cream colour becomes tannish -flat or slightly heaped, shiny, smooth edges
- 18. Other media Inositol agar with chloramphenicol - inhibits Candida growth -used for inoculation of urine and pallets from centrifuged bronchial secretions -inositol is a unique carbon source -assimilated by Cryptococcus spp. -incubation: 3-5 days colonies- do not produce hyphae or pseudo-hyphae.
- 19. Niger seed agar, caffeic acid agar and bird seed agar -demonstrate melanin production: brown coloured colonies - C. neoformans breaks down caffeic acid to melanin -Growth at 37°C. 3. Biochemical confirmation -urease test: positive. -assimilation of inositol, maltose, sucrose, dextrose, galactose, xylose and nitrate. - Not fermentative
- 20. 4. Mouse pathogenicity test -inoculation of colonies in mice: intracerebral or intraperitoneally. -fatal for mice. -Capsulated budding yeast cells: demonstrated in the brain of infected mice.
- 21. 5. Immuno-serology Ag detection - Detects polysaccharide antigen of C. neoformans in fluids. - High titre in serum, intermediate in CSF and lowest in urine. - Bronco- alveolar lavage (BAL): also tested for Cryptococcal Ag. Latex agglutination Test (LAT) - Slide agglutination test: uses latex particles coated with polyclonal or monoclonal antibodies. - Positive test: is done at dilution 1:4 - Titre ≥ 1: 8 indicates active disease. - Higher Ag titre: indicate severe infections - Falling titre: good prognostic sign.
- 22. Treatment Amphotericin B 5- fluorocytosine imidazoles (miconazole, keratonazole) Triazoles (itranazole, fluconazole, voriconazole) Echinocandins (caspofungin, micafungin)
- 23. THANK YOU