CRYPTOCOCCOSIS

Cryptococcosis is a systemic infection that likes the CNS and is caused by the encapsulated yeast C. neoformans. It doesn’t form hyphae, has a polysaccharide capsule, does not ferment, and its sexual state is called Basidimycete. The yeast can affect the pulmonary system and be asymptomatic or symptomatic and cause pneumonia with a cough, weight loss, night sweats, etc. It can invade the CNS and cause chronic meningitis, meningo-encephalitis, or brain abscess – this can cause misdiagnosis for brain tumors. The infection could also invade bones and skin (10-15%).

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C. neoformans is the main pathogen of the cryptococcus genus. It has several virulence factors:

1. Capsule  major compartment is the polysaccharide Glucoroxylomannan made of mannose, xylose, glucoronic acid. The capsule can induce antibiotics and is used to determine serotypes. There are 4 – A &D have many similarities and are the neoformans group of C. neoformans. B&C have similarities and are part of the gatti group of C. neoformans.

2. Grows at 37 degrees

3. Makes phenol oxidase

4. Makes urease

Mode of Infection

Serotypes A and D live in soil contaminated with pigeon droppings and are pretty much universal. B and C probably live in soil around Eucalyptus trees, and are associated with tropical and subtropical areas. Infection is by inhalation, but the capsule seems like it’s too large to get into the alveoli, so how does it infect people? We don’t really know, but one theory is that the capsule is kinda shrunk when it’s inhaled. Once it gets inside it forms the full on capsule.

Host Defense

Neutrophils and monocytes ingest and kill the little buggers via oxidative and non-oxidative pathways. T-cells cause the release of cytokines and lead to increased resistance. People get acquired resistance following infection by cell mediated immunity and antibodies.

Predisposing conditions include AIDS patients, lymphomas (especially Hodgkins), organ transplants, and most importantly, any type of impaired cell mediated immunity.

Diagnosis  seeing encapsulated yeasts in a specimen, culturing it on a plate (there’s no problem of it being part of the normal flora like in candida), and immunodiagnosis. Treatment in non-AIDS patients is to give AMB/ lipsomal AMB, and in AIDS patients you start of the same way and then give flucanazole as a maintenance treatment.

It’s important to remember that leukemics get more systematic fungal candida infections and HIV patients get more local infections. Cryptococcus is a lethal disease in AIDS patients and can be in up to 30% of patients (in Africa). Candida is seen in about 85% of AIDS patients.

Category: Microbiology Notes