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The Fungi of Medical Importance. Chapter 22. Fungi as infectious agents. molds & yeasts are widely distributed in air, dust, fomites & normal flora humans are relatively resistant fungi are relatively nonpathogenic

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Fungi as infectious agents
Fungi as infectious agents

  • molds & yeasts are widely distributed in air, dust, fomites & normal flora

  • humans are relatively resistant

  • fungi are relatively nonpathogenic

  • of the 100,000 fungal species, only 300 have been linked to disease in animals

  • fungi are the most common plant pathogens

  • human mycoses are caused by both true pathogens and opportunistic pathogens


Mycoses general statements on
Mycoses (general statements on)

  • Most fungal pathogens do not require a host to complete their life cycles and infections are not communicable

  • Dermaphytes & Candida sp naturally inhabit human body & are transmissible

  • Dermaphytoses most prevalent fungal infection

  • Most cases go undiagnosed or misdiagnosed

  • Infections can be systemic, subcutaneous, cutaneous or superficial



Mycoses
Mycoses

  • immunity to fungal infections consist of nonspecific barriers, inflammation & cell mediated defenses

  • diagnosis & identification require microscopic examination of stained specimens, culturing in selective & enriched media & specific biochemical & serological tests

  • control with Antifungals such as amphotericin B, flucytosine, azoles & nystatin


Antifungal therapies
Antifungal 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 use


Systemic mycoses caused by true pathogens
Systemic mycoses caused by true pathogens

  • Thermal dimorphism

  • Restricted to certain endemic regions of the world

  • Soil is normal habitat

  • Infection by inhalation of spores  Pulmonary infections

    • Histoplasma capsulatum

    • Coccidioides immitis

    • Blastomyces dermatitidis

    • Paracoccidioidomycosisbrasiliensis


Thermal Dimorphism

25 degrees - Hyphal state………………..37 degrees – Yeast state

Thermal dimorphism is a property of true fungal pathogens but is uncommon for opportunistic pathogens



Histoplasma capsulatum
Histoplasmacapsulatum

  • causes histoplasmosis

  • typically dimorphic

  • distributed worldwide, most prevalent in eastern & central regions of US

  • grow in moist soil high in nitrogen content (bat and bird droppings)

  • Inhalation of organism produces primary pulmonary infection that may progress to systemic involvement of a variety of organs & chronic lung disease

  • amphotericin B, ketoconazole


Histoplasma capsulatum1
Histoplasma capsulatum

Areas with large amounts of bird droppings are esp. dangerous


Coccidioides immitis
Coccidioidesimmitis

  • causes coccidioidomycosis

  • dimorphic

  • lives in alkaline soils in semiarid, hot climates & is endemic to southwestern US

  • spores inhaled from dust leads to primary pulmonary infection which can progress to system body-wide disease

  • amphotericin B treatment



Coccidioides immitis2
Coccidioides immitis

Disseminated coccidiomycosis


Blastomyces dermatitidis
Blastomycesdermatitidis

  • causes blastomycosis

  • dimorphic

  • free-living species distributed in soil of a large section of the midwestern and southeastern US

  • inhaled spores convert to yeasts & multiply in lungs

  • symptoms include cough & fever

  • chronic cutaneous, bone, & nervous system complications

  • amphotericin B


Blastomyces dermatitidis1
Blastomyces dermatitidis

Hyphal state

Yeast state


Blastomyces dermatitidis2
Blastomycesdermatitidis

Cutaneous blastomycosis


Paracoccidioidomycosis brasiliensis
Paracoccidioidomycosisbrasiliensis

  • Distributed in Central & South America

  • Infections of the lung or skin

  • Most infections are self-limiting, systemic disease is not common

  • Ketoconazole, amphotericin B, sulfa drugs

Budding yeast


Subcutaneous mycoses
Subcutaneous mycoses

  • Invade traumatized skin, rarely become systemic but can cause destructive local lesions

    • lymphocutaneous sporotrichosis

    • chromoblastomycosis

    • mycetoma


Sporothrix schenckii
Sporothrixschenckii

  • sporotrichosis (rose-gardener’s disease)

  • very common saprobic fungus that decomposes plant matter in soil

  • infects appendages & lungs

  • Lymphocutaneous variety occurs when contaminated plant matter penetrates the skin & the pathogen forms a nodule, then spreads to nearby lymph nodes


Lymphocutaneous sprotrichosis
lymphocutaneous sprotrichosis

Primary sore and series of secondary nodules along lymphatic chain in the arm


Mycetoma
mycetoma

  • when soil microbes are accidentally implanted into the skin

  • progressive, tumorlike disease of the hand or foot due to chronic fungal infection; may lead to loss of body part

  • caused by Pseudallescheria or Madurella


Cutaneous mycoses
Cutaneous mycoses

  • infections strictly confined to keratinized epidermis (skin, hair, nails) are called dermatophytoses-ringworm

  • 39 species in the genera Trichophyton, Microsporum, Epidermophyton

  • communicable among humans, animals, & soil

  • infection facilitated by moist, chafed skin


  • Ringworm of scalp (tinea capitis) affects scalp & hair-bearing regions of head; hair may be lost

  • Ringworm of body (tinea corporis) occurs as inflamed, red ring lesions anywhere on smooth skin

  • Ringworm of groin (tinea cruris) “jock itch” affects groin & scrotal regions

  • Ringworm or foot & hand (tinea pedis & tinea manuum) is spread by exposure to public surfaces; occurs between digits & on soles. (Athlete’s foot)

  • Ringworm of nails (tinea unguium) is a persistent colonization of the nails of the hands & feet that distorts the nail bed


Ringworm hair-bearing regions of head; hair may be lost


Ringworm / Dermatophytosis hair-bearing regions of head; hair may be lost


Ringworm treatment
Ringworm treatment hair-bearing regions of head; hair may be lost

  • ointments containing tolnaftate, miconazole or menthol & camphor

  • lamisil or griscofulvin 1-2 years


Superficial mycoses
Superficial mycoses hair-bearing regions of head; hair may be lost

  • Tineaversicolor causes mild scaling, mottling of skin

  • White piedra is whitish or colored masses on the long hairs of the body

  • Black piedra causes dark, hard concretions on scalp hairs

    • White & black piedra

      • Transmission is often mediated by shared hair brushes or combs

      • Several members of a family are usually infected at the same time

      • Infected areas must often be shaved to remove the fungi


Tinea versicolor hair-bearing regions of head; hair may be lost


Black piedra
Black Piedra hair-bearing regions of head; hair may be lost


White piedra
White Piedra hair-bearing regions of head; hair may be lost


Opportunistic mycoses
Opportunistic Mycoses hair-bearing regions of head; hair may be lost


Table hair-bearing regions of head; hair may be lost


Candida albicans
Candida albicans hair-bearing regions of head; hair may be lost

  • widespread yeast

  • infections can be short-lived, superficial skin irritations to overwhelming, fatal systemic diseases

  • budding cells of varying size that my form both elongate pseudohyphae & true hyphae

  • forms off-white, pasty colony with a yeasty odor


Candida albicans1
Candida albicans hair-bearing regions of head; hair may be lost

  • Normal flora of oral cavity, genitalia, large intestine or skin of 20% of humans

  • Account for 80% of nosocomial fungal infections

  • Account for 30% of deaths from nosocomial infections

  • Thrush – occurs as a thick, white, adherent growth on the mucous membranes of mouth & throat

  • Vulvovaginal yeast infection – painful inflammatory condition of the female genital region that causes ulceration & whitish discharge

  • Cutaneouscandidiasis– occurs in chronically moist areas of skin and burn patients


Candida albicans2
Candida hair-bearing regions of head; hair may be lostalbicans

Thrush

Candidal diaper rash

Vaginitis


Cryptococcus neoformans
Cryptococcus neoformans hair-bearing regions of head; hair may be lost

  • a widespread encapsulated yeast that inhabits soils around pigeon roosts

  • causes cryptococcosis

  • common infection of AIDS, cancer or diabetes patients

  • infection of lungs leads to cough, fever, & lung nodules

  • dissemination to meninges & brain can cause severe neurological disturbance & death


Cryptococcus neoformans1
Cryptococcus neoformans hair-bearing regions of head; hair may be lost


Pneumocystis jiroveci p carinii
Pneumocystis hair-bearing regions of head; hair may be lostjiroveci(P.carinii)

  • a small, unicellular fungus that causes pneumonia (PCP), the most prominent opportunistic infection in AIDS patients

  • this pneumonia forms secretions in the lungs that block breathing & can be rapidly fatal if not controlled with medication

  • pentamidine & cotrimoxazole


Aspergillus
Aspergillus hair-bearing regions of head; hair may be lost

  • very common airborne soil fungus

  • 600 species, 8 involved in human disease

  • inhalation of spores causes fungus balls in lungs and invasive disease in the eyes, heart, & brain

  • amphotericin B & nystatin


Aspergillus1
Aspergillus hair-bearing regions of head; hair may be lost

Invasive eye infection

Conjunctival infection

Brain abscesses (darkened areas)


Zygomycosis
zygomycosis hair-bearing regions of head; hair may be lost

  • Zygomycota are extremely abundant saprobic fungi found in soil, water, organic debris, & food

  • Genera most often involved are Rhizopus, Absidia, & Mucor

  • usually harmless air contaminants invade the membranes of the nose, eyes, heart, & brain of people with diabetes, malnutrition with severe consequences


Hyphae and spores of zygomycosis-causing fungus hair-bearing regions of head; hair may be lost


Fungal allergies mycotoxicoses
Fungal allergies & mycotoxicoses hair-bearing regions of head; hair may be lost

  • Fungal spores are common sources of atopic allergies

  • asthma, often occurring in seasonal episodes

  • farmer’s lung, a chronic & sometimes fatal allergy of agricultural workers exposed to moldy grasses

  • teapicker’s lung

  • bagassosis, a condition caused by inhaling moldy dust from processed sugarcane debris

  • bark stripper’s disease caused by inhaling spores from logs

  • Fungal toxins lead to mycotoxicoses

    Some may be caused by eating poisonous or hallucinogenic mushrooms

    Ergot poisoning can occur from ingestion of moldy grain


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