Cryptococcosis: Introduction, Pathogenesis, Laboratory Diagnosis, Treatment, Prevention and Control
Introduction of Cryptococcosis
Cryptococcosis is an acute, subacute, or chronic pulmonary meningeal mycosis caused by Cryptococcus neoformans. It is a soil saprophyte and is particularly abundant in the feces of pigeons( pigeon’s dropping). It does not appear to infect birds, probably because of their high body temperature and infection throughout the world.
Classification of Cryptococcus
Species: C. neoformans
Other species are-
C. albidus ( nitrate positive)
C. laurentii ( melibiose fermentation)
C. gattii ( Trehalose positive)
C. neoformans: All are negative
C. neoformans var. grubii ( serptype A)- world-wide distribution
C. neoformans var. neoformans (serotype D)-Restricted distribution and prevalent in France, Italy, and Denmark.
Morphology of Cryptococcus
It is a yeast characterized by wide polysaccharide capsule and budding, found both in culture and tissue fluid. It is a true yeast and is Gram-positive. The capsule may be identified by India ink or nigrosin preparation.
Size: 5-15 µm
Based on carbohydrate antigen, there are 4 serotypes e.g. A, B, C, and D. Infection due to serotypes A and B are common.
Phenol oxidase enzyme
Growth rate at 37°C
Source of infection
Infection is usually acquired by inhalation of dust-containing yeast cells.
The disease is usually seen in immunosuppressed hosts and most infections are asymptomatic. Pulmonary cryptococcosis may lead to mild pneumonitis. Cryptococcal meningitis happens by hematogenous spread and is often seen in AIDS patients. Skin, lymph nodes, bones, and other organs may be involved when the dissemination of infection takes place. Cutaneous cryptococcosis varies from small to ulcers to large granuloma. Visceral forms of cryptococcal infection stimulate tuberculosis and cancer clinically.
India ink preparation
positive due to having capsule appearing as a clear halo around the yeast cells as shown above figure. Gram stain: Gram-positive yeast cells as shown above figure. The histopathological examination of tissue can be done by staining with H/E, PAS, and mucicarmine stains.
Lactophenol cotton blue mount shows budding yeast cells as shown below.
Birdseed agar (BSA): It is a selective medium for Cryptococcus. C. neoformans produces brown colonies within a week at 30°C, such property is not shown by other yeasts. Cryptococcus neoformans produces phenoloxidase, which oxidizes the caffeic acid in the niger seed(resemble sunflower seeds in shape but are smaller in size and black that contains proteins, oil, and soluble sugars, botanical name-Guizotia abyssinica) into melanin.
i.e. Phenol oxidase
Caffeic acid…………Brown pigment
Latex agglutnation test
Capsular polysaccharide antigen may be detected in CSF, serum, or even in urine by this latex agglutination test.
Animal Inoculation test
C. neoformans inoculation into mice through intracerebral or intraperitoneal routes creates a fatal infection. Encapsulated budding yeast cells can be demonstrated in the brain of the infected mice.
Urea Hydrlolization Test
It shows urea hydrolyzation test positive.
Sugar fermentation and assimilation test
They do not ferment carbohydrates.
Detection of C. neoformans DNA in tissue samples by Nested and Real-Time PCR Assays
Treatment of Cryptococcosis
Prevention and Control
People having Immunocompromized or Immunosuppressed status should avoid contact with birds and avoid digging and dusty activities in areas heavily contaminated with bird droppings.
Avoid the area where availability of dried pigeon feces.
Wear masks to prevent the inhalation of C. neoformans.