The Fungi of Medical Importance

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The Fungi of Medical Importance
Chapter 22
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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

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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

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Levels of invasion
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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

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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

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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
• Paracoccidioidomycosis brasiliensis

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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
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Distribution of True Fungal Pathogens
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Histoplasma capsulatum

• 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

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Histoplasma capsulatum
Areas with large amounts of bird droppings are
esp. dangerous
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Coccidioides immitis

• 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

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Coccidioides immitis
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Coccidioides immitis
Disseminated coccidiomycosis
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Blastomyces dermatitidis

• 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

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Blastomyces dermatitidis
Hyphal state
Yeast state
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Blastomyces dermatitidis
Cutaneous blastomycosis
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Paracoccidioidomycosis brasiliensis

• 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
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Subcutaneous mycoses

• Invade traumatized skin, rarely become systemic
  but can cause destructive local lesions
• lymphocutaneous sporotrichosis
• chromoblastomycosis
• mycetoma

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Sporothrix schenckii

• sporotrichosis (rose-gardeners 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

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

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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

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

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Ringworm
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Ringworm / Dermatophytosis
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Ringworm treatment

• ointments containing tolnaftate, miconazole or
  menthol camphor
• lamisil or griscofulvin 1-2 years

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Superficial mycoses

• Tinea versicolor 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

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Tinea versicolor
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Black Piedra
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White Piedra
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Opportunistic Mycoses
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Table
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Candida albicans

• 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

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Candida albicans

• 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
• Cutaneous candidiasis occurs in chronically
  moist areas of skin and burn patients

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Candida albicans
Thrush
Candidal diaper rash
Vaginitis
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Cryptococcus neoformans

• 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

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Cryptococcus neoformans
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Pneumocystis jiroveci (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

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Aspergillus

• 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

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Aspergillus
Invasive eye infection
Conjunctival infection
Brain abscesses (darkened areas)
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zygomycosis

• 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

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Hyphae and spores of zygomycosis-causing fungus
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Fungal allergies mycotoxicoses

• Fungal spores are common sources of atopic
  allergies
• asthma, often occurring in seasonal episodes
• farmers lung, a chronic sometimes fatal
  allergy of agricultural workers exposed to moldy
  grasses
• teapickers lung
• bagassosis, a condition caused by inhaling moldy
  dust from processed sugarcane debris
• bark strippers 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