1MicrobiologyWith Diseases by TaxonomySecond EditionPowerPoint®Lecture SlidesCopyright © 2007 Pearson Education, Inc. publishing asBenjamin Cummings17Pathogenic FungiCopyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsMedical Mycology Field of medicine concerned with the diagnosis, management, and prevention of fungal diseases or mycoses Mycoses are among the most difficult diseases to diagnose and treat Signs of mycoses are often missed or misinterpreted Fungi are often resistant to antifungal agentsCopyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsEpidemiology of Mycoses Fungi and their spores are almost everywhere in the environment Because they are widespread, most people will experience a mycosis at some time Typically acquired via inhalation, trauma, or ingestion Infrequently spread from person-to-person  Most mycoses are not contagious Dermatophytes, fungi found on the skin, are the major exception2Copyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsEpidemiology of Mycoses Epidemics result from mass exposure to some environmental source of fungi Mycoses are generally not reportable and thus adequate information on their occurrence and spread is often lackingCopyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsCategories of Fungal Agents Only four fungi are usually considered true pathogens Have the ability to actively attack and invade tissues Exhibit dimorphism Based on differences in temperature In the environment they have mycelium thallicomposed of hyphae and within the body they exist as yeast thalli Yeast forms are invasive due to the production of various enzymes and proteins that allow their survival within the body Endemic to certain regions, primarily in the AmericasCopyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsCategories of Fungal Agents Opportunistic fungi account for the remaining diseases in humans Often commensals that take advantage of a weakness in a host’s defenses Distributed throughout the world Dermatophytes are considered in this group because they often occur in individuals susceptible to opportunistic fungi Four factors increase an individual’s risk for acquiring an opportunistic mycoses3Copyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsFactors that Predispose Individuals to Opportunistic MycosesTable 22.1Copyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsClinical Manifestations of Fungal Disease Fungal diseases are grouped in three categories of clinical manifestation Fungal infections Most common mycoses Caused by the presence in the body of either true pathogens or opportunists Toxicoses Acquired through ingestion Occurs when poisonous mushrooms are eaten Allergies Most often result from the inhalation of fungal spores Copyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsDiagnosis of Fungal Infections A patient’s history is critical for diagnosis of most mycoses Definitive diagnosis often requires isolation, laboratory culture, and morphological analysis of the fungus involved Sabouraud dextrose agar is used to culture fungi collected from patients This medium favors fungal growth over bacterial growth Various techniques are used to detect fungal cells in patient specimens4Copyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsDiagnosis of Fungal Infections Immunological tests are not always useful for fungi Due to the prevalence of fungi in the environment it is often hard to distinguish between an infection and simple exposure Opportunistic infections are particularly difficult to diagnose Fungi can display abnormal morphology in tissues where infection wouldn’t normally occurCopyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsAntifungal Therapies Mycoses are among the most difficult diseases to heal Fungi can often resist the oxidative damage of T cells during cell-mediated immune responses Fungi are biochemically similar to human cells and antifungal drugs can harm human tissues Fungi have ergosterol in their membranes rather than cholesterol and it is often a target for antifungal treatment Side effects can still result, especially with long-term useCopyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsAntifungal Therapies Amphoterecin B is the “gold standard” of antifungal agents but also the most toxic Other antifungal agents include various azole drugs, fluorocytosine, and griseofulvin Opportunistic infections treatment requires two steps High-dose treatment to eliminate or reduce the fungal pathogens Long-term maintenance therapy to control and prevent reinfection5Copyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsSystemic Mycoses Caused by Pathogenic Fungi Infections spread throughout the body Caused by one of the four pathogenic, dimorphic fungi of the division Ascomycota Blastomyces, Coccidioides, Histoplasma, andParacoccidioides Acquired through inhalation Begin as a generalized pulmonary infection that disseminates via the blood to the rest of the body Individuals working with dimorphic fungi in the laboratory must take multiple precautions to avoid exposure to sporesCopyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsBlastomycosis Blastomyces dermatitidis is the causative agent Endemic in the southeastern United States north to Canada Fungi found in soils rich in organic matter Inhalation of dust can carry fungal spores or hyphalpieces into the lungs Pulmonary blastomycosis is the most common manifestation in humans Initial pulmonary lesions are mostly asymptomatic and symptoms, when they develop, are often vague The disease resolves in most people but in others it may be chronic Treatment is with amphotericin BCopyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsBlastomycosisFigure 22.36Copyright © 2007 Pearson Education, Inc. publishing asBenjamin CummingsSystemic Mycoses Caused by Opportunistic Fungi Opportunistic mycoses don’t typically affect healthy humans Infections usually limited to people with poor immunity Becoming more important as the number of immunocompromised individuals rises Can be difficult to identify because