Primary pathogens can establish infections in normal hosts. Opportunistic pathogens cause disease in individuals with compromised host defense mechanisms.
The primary pathogens have relatively well-defined geographic ranges; the opportunistic fungi are ubiquitous.
Current magnitude and problems of mycoses
Fungal infections or mycoses cause a wide range of diseases in humans. Mycoses range in extent from
superficial infections involving the outer layer of the stratum corneum of the skin to disseminated infection involving the brain, heart, lungs, liver, spleen, and kidneys. The range of patients at risk for invasive fungal infections continues to expand beyond the normal host to encompass patients with the acquired immunodeficiency syndrome; those immunosuppressed due to therapy for cancer and organ transplantation, and those undergoing major surgical procedures. Each of these patient populations has a high risk of developing invasive fungal infections. As the population at risk continues to expand so also does the spectrum of opportunistic fungal pathogens infecting these patients also continue to increase. Many of the deeply invasive mycoses are difficult to diagnose early and often difficult to treat effectively.The development of new approaches to diagnosis and treatment of invasive fungal infections is the subject of intensive research.
Superficial mycoses are limited to the stratum corneum and essentially elicit no inflammation.
Cutaneous infections involve the integument and its appendages, including hair and nails. Infection may involve the stratum corneum or deeper layers of the epidermis. Inflammation of the skin is elicited by the organism or its products.
Subcutaneous mycoses include a range of different infections characterized by infection of the subcutaneous tissues usually at the point of traumatic inoculation. An inflammatory response develops in the subcutaneous tissue frequently with extension into the epidermis.
Deep mycoses involve the lungs, abdominal viscera, bones and or central nervous system. The most common portals of entryare the respiratory tract, gastrointestinal tract, and blood vessels (Fig. 75-2).