Cryptococcus neoformans fungi, light micrograph. An India ink stain has been used, which enhances the acidic mucopolysaccharide capsules (luminous rings) that cover and protect the cells. This yeast-like fungus causes cryptococcosis, a rare infection that affects people with a deficient immune system such as in AIDS. It is caused by inhaling the fungus from soil contaminated by pigeon droppings. Infection may cause meningitis or granular growths in the lungs, skin or elsewhere.