Primary fungal diseases

Invasive infections of the internal organs with the fungus gaining entry by the lungs, gastrointestinal tract or through intravenous lines. They may be caused by: (1) primary pathogenic fungi or (2) by opportunistic fungi that are of marginal pathogenicity but can infect the immunocompromised host.

Invasive fungal infections are increasing causes of morbidity and mortality in hospitalized patients for several reasons: (1) The widespread use of potent broad-spectrum antibiotics allows fungal overgrowth; (2) The increasing application of critical care services has given rise to larger numbers of patients with indwelling catheters and various host defences that are compromised in multiple ways; (3) Chemotherapy regimens have intensified, and new immunomodulatory therapies have been introduced for the management of neoplastic diseases; (4) Organ transplantation occurs for ever-increasing indications in modern medical practice. As a consequence, not only is the pool of susceptible patients growing, but with more effective antibacterial treatments, superinfections by fungi are more likely.

Dimorphism is a characteristic of fungi causing primary systemic disease. These agents charateristically have two alternative phenotypes (yeast and mould). They may exist in nature in the mould form but when invading the host ,they assume an aborted yeast form. This transformation may initiated by various factors, of which temperature change is common.

Primary pathogenic fungi cause primary systemic fungal disease. Infection occurs in previously healthy persons and arises through the respiratory route. Examples include histoplasmosis, blastomycosis, coccidiomycosis and paracoccidiodomycosis. The fungi occur throughout the world.

During the 1980s, the rate of fungal infections in hospitalized US patients doubled, with increases occurring in both medical and surgical patient populations. During the 1990s, this trend did not abate. At the same time, mortality from Candida infection in hospitalized patients declined, because of improvements in both early detection (through heightened awareness and improvements in culture techniques) and management of invasive Candida infections. In contrast, there was a relentless rise in mortality from Aspergillus infection, which has now surpassed the mortality rate from Candida infection.