Cryptococcus neoformans - the encapsulated menace

Abstract

Opportunistic fungal infections have emerged in the past ten to twenty years as some of the most significant and potentially lethal infectious diseases to confront contemporary medicine. Fungi such as Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans have emerged from obscurity to threaten many patient groups. Although the latter of these, the yeast C. neoformans, was identified as a potential pathogen as early as 1894, it was not until the 1950s that a systematic appreciation of its potential as an opportunistic pathogen began. During this decade the association between the heightened risk of C. neoformans infection (cryptococcosis) and various cancers of the blood became obvious. Fortunately, just as the risk posed by this yeast to human health was being clearly defined (in the late 1950s), the first effective therapy to treat cryptococcosis appeared - the drug amphotericin B. This was particularly timely since it had been recognised that C. neoformans infection often led to a rapidly fatal form of meningitis if untreated.

Throughout the 1960s the infection remained relatively rare, being largely confined to the patient group described above. However, by the late 1970s the incidence of C. neoformans infection began to rise rapidly. Cases were now being seen in patients undergoing organ transplantation, in those with autoimmune diseases and in others who were receiving immunosuppressive drugs to treat various cancers. Cryptococcosis had suddenly become 'the awakening giant' amongst fungal infections (Kaufman & Blumer,1977); but quite how much of a ‘giant’ would only become clear in the next two decades with the development of the human immunodeficiency virus (HIV) epidemic.