Infections by Cryptococcus species

Abstract

Cryptococcosis is a serious infectious disease that can affect both immunocompetent and immunocompromised patients. However, the majority of cases are related to patients with acquired immunodeficiency syndrome (AIDS). Cryptococcus neoformans and Cryptococcus gattii are environmental yeasts and are recognized as the main etiological agents responsible for these infections. In healthy persons, the infection is controlled by the immune response, but in people with compromised immune systems, the yeasts can disseminate and invade the central nervous system. These fungi have several particular features that make them unique among fungal pathogens. They possess a polysaccharide capsule that confers protection against stress factors and causes damage in the host. The capsule is a dynamic structure, because it can change its structure and density. Cryptococcus spp. also accumulates melanin which is required for virulence. Furthermore, they are considered intracellular fungal pathogens because they survive inside macrophages. A very peculiar feature of this fungus is its ability to induce a massive growth of the cell during infection, which leads to the formation of “titan cells.” These cells contribute to immune evasion and to long-term maintenance of the yeast in the host. The therapy used for cryptococcosis is based on amphotericin B, fluconazole, and 5-fluorocytosin. However, the treatment of cryptococcosis presents some limitations, and mortality associated to this disease remains high.