Chapter 22: Pathogenic Fungi

Where are fungi found?

They are found everywhere in the environment

Growing on decaying plants and animal matter, in soil, airborne spores, normal microbiota of multicell organisms, and humans

How many species of fungi are associated with human disease?

fewer than 200 of the 100,000

Do Healthy Humans generally resistant to fungal infections

Yes

Opportunistic Fungal Pathogen: Cutaneous Mycoses

Dermatophytes: feed on keratin, contagious

Treatment topical antifungal

True Fungal Pathogen: Pathogenesis

Entry through respiratory tract: inhaled spores

Thermal dimorphism (virulence factor)

Endemic

Usually asymptomatic/mild disease

Capable of causing severe, disseminated disease

Thermal Dimorphism

filamentous in the environment, yeast form at human body temp.

Control of Infections

Diagnosis is difficult and immunization not usually effective

Treatment can be difficult - few antifungal drugs increase drug resistance, selective toxicity difficult to achieve - euk.

Ergosterol “Gold Standard”

Various risk factors increase risk of mycoses - immunocompromised

Histoplasmosis: Ohio Valley Fever

caused by Histoplasma capsulatum - most common fungal true pathogen

most prevalent in eastern and central U.S. but is world wide too

Grows in moist soil rich in nitrogen, often associated with bird roosts

95% asymptomatic and 5% more severe disease - Chronic pulmonary, cutaneous, systemic, or ocular disease

Histoplasmosis: Ohio Valley Fever - Virulence Factors

thermotolerant, escape phagocytosis intracellular replication in macrophages aids in dissemination from lungs

Coccidioidomycosis: Valley Fever

caused by coccidioides immits and coccidioides posadasii

Found sporadically in alkaline soils in semiarid climates

Endemic

High winds that pick up cordidia - Haboob/Munsoon

Inhauled

Most immunocompetent effectively clear organism

Begins as pulmonary infection, but can become disseminated

Coccidioidomycosis: Valley Fever - Morphology

block like arthroconidia in the free living stage and spherules

Coccidioidomycosis: Valley Fever - Treatment

Amphotericin B