Fungi in Tissue Lab-5-

Fungi in Tissue (con’t.) 1.) Yeasts: These vary in size, shape, method of dividing, with of without a capsule, etc. The following illustrates several distinguishing features of yeasts and the diseases they cause:

a.) Only one pathogenic yeast has a capsule. The disease it causes is called Cryptococcosis: -Fatal disease of brain (CSF), causing meningitis -encapsulated yeast seen in India ink -fluconazole and itraconazole -5 cases/million normal population but >20% AIDS

Pulmonary cryptococcosis PAS stain showing encapsulated yeast in tissue

C. neoformans culture grown at either 24  C or 35  C. Organism is monomorphic. C. neoformans as seen in culture or in CSF. Note huge capsule.

b.) Two mycoses have intracellular yeast. One of these is Histoplasmosis and the other is Penicilliosis. Histoplasmosis -Granulomatous disease of lungs and RES which mimics TB. -Spread from bird droppings, especially blackbirds, chickens and bats. -Worldwide -Hard to diagnose, use itraconazole.

Small (3-5 microns) intracellular yeast of H. capsulatum Blood smear showing three intracellular yeast of H. capsulatum

Infectious form of Histoplasma capsulatum showing spores. In nature or lab at 24  C. Yeast (pathogenic) form as in vivo or cultured at 35  C. This is a dimorphic fungus.

The second intracellular yeast causes Penicilliosis. This is a relatively new disease that is found exclusively in S. China and S.E. Asia. It is the number 3 cause of death for AIDS patients in Thailand. Note characteristic “target” lesions of penicilliosis.

Note the numerous intracellular yeast. The infectious form of Penicillium marneffei as seen in nature or 24  C lab. Dimorphic Penicillium marneffei

Sporotrichosis is caused by another dimorphic yeast called “gardener’s disease”, acquired from plants. Characteristic lymphadenopathy. Patient on right has secondary bacterial infection.

Dimorphic cultures of Sporothrix schenckii Infectious form cultured at 24  C. Pathogenic (yeast) cultured at 35  C

Fungi in Tissue (con’t.) 2.) Sporangia. These are large (20-40 microns), round elements which contains numerous spores. They cause coccidioidomycosis which is endemic to SW United States and Mexico. It is a fatal lung disease found mostly in Asians and dark-skinned people. Skin lesions in coccidioidomycosis.

The organism Coccidioides immitis is found in desert soils as shown here. The spores become airborne, enter the lungs and change into endospores.

Dimorphic forms of Coccidioides immitis PAS stain showing sporangia in lung tissue. Highly infectious spores growing in soil or in the laboratory.