Chapter 22: Fungal Pathogens

How are molds yeast widely distributed?

distributed in air, dust, fomites, and normal flora

What is the most common plant pathogen?

fungi

What are human mycoses caused by?

true fungal pathogens and opportunistic pathogens

What are the primary true pathogens?

Blastomyces dermatitidis- causes Blastomycosis

Coccidioides immitis- causes Coccidioidmycosis

Pathogens with Intermediate Virulence

Sporothrix schenckii- causes sporotrichosis

Genera of dermatophytes (Microsporum, Trichophyton, Epidermophyton)- causes dermatophytosis (various ringworms or tineas)

Why do HIV/AIDS patients die from opportunistic pathogens?

due to weaken immune system

associated w/candida albicans

True/Primary fungal pathogens

can invade and grow in a healthy non-compromised host

Thermal Dimorphism

small number of fungi that can switch from hyphal cells to yeast cells

Grow as molds at 30^oC and as yeasts at 37^oC

Opportunistic fungal pathogen

has little or no virulence; host defenses must be impaired

Emerging Fungal Pathogens

vary from superficial and colonization to potentially fatal systemic disease

10% of nosocomial (hospital origin) infections

Dermatophytes may be undergoing transformation into tru pathogens

Candida auris- blood borne fungal pathogen

candida albicans

Do most fungal pathogens require a host?

most DO NOT require a host to complete their life cycles and infections are not communicable

Epidemiology of Mycoses

Dermaphytes and candida sp naturally inhibit human body and can go undiagnosed of misdiagnosed

Dermaphytoses are most prevalent

True fungal pathogens are distributed in a predictable geographical pattern- climate, soil

Portal of entry in primary mycoses

respiratory portal; inhaled spores

Portal of entry in subcutaneous

inoculated skin; trauma

Portal of entry in cutaneous and superficial

contamination of skin surface (burns)

Virulence factors

thermal dimorphism, toxin-like substances, capsules and adhesion factors, hydrolytic enzymes, inflammatory stimulants

all these can cause disease

Host anti-fungal defenses

integrity of skin, mucous membranes and respiratory cilia

most important are cell-mediated immunity, phagocytosis, and inflammation

long term immunity can only develop for some true pathogens

What is required for diagnosis and identification for mycitic infections?

microscopic viewing of stained specimens

culturing in selective and enriched media

specific biochemical and serological tests

Control of Mycotic infections

immunization is not usually effective

prevention limited to masks and protective clothing to reduce contact with spores

in some cases surgical removal

Systemic Infections by True pathogens

restricted to endemic regions of the world

infection occurs when matter containing conidia is distributed

spores germinate in lungs, infection can become systemic, spores may be inoculated into the skin

all diseases result in immunity

Coccidioidomycosis: Valley Fever

block-like arthroconidia in free-living stage, spherules containing endospores in lungs

What causes causes coccidioidomycosis?

coccidioides immitis

How does infection develop for valley fever?

arthrospores inhaled from dust creates spherules in the lungs that release spores

infection may develop into infection of the skin, bones, and CNS

In chronic pulmonary disease; nodules in the lungs (fungomas)

North American Blastomycosis

dimorphic (can be hyphae phase or yeast phase)

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

occurs in tissues

What causes North American Blastomycosis?

blastomyces dermatitidis

How does infection occur in North American Blastomycosis?

inhaled 10-100 conidia convert to yeasts and multiply in lungs

symptoms include: cough and fever

chronic cutaneous, bone, and nervous system complications

Subcutaneous Mycoses

when fungi are transferred directly into traumatized skin, they can invade the damaged site

involved with tissues within and below the skin

most species in this group are greatly inhibited by higher temps of blood and viscera

diseases are progressive

What are the 2 mycoses?

sporotrichosis and mycetoma

Sporotrichosis- Rose Gardener’s disease

infects appendages and lungs

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

What causes Sporotrichosis?

sporothrix schenckii

Mycetoma

when soil microbes are accidentally implanted into the skin

progressive, tumor like disease of the hand, foot due to chronic fungal infection; may lead to loss of a body part

What causes mycetoma?

Pseudallescheria or madurella

Dermatophytoses

Ringworm and tinea

Infections strictly confined to keratinized epidermis (skin, hair, nails)

Cutaneous Mycoses

Natural reservoirs- humans, animals, and soils

Hardiness of the dermatophyte spores, presence of abraded skin, and intimate contact promote infection

Long infection period following by localized inflammation and allergic reactions to fungal pathogens

What are the three Dematophyte Genera?

Trichophyton, microsporum, epidermophyton

Name of disease caused by Trichophyton

Ringworm of the scalp, body, beard, and nails

Athlete’s foot

Principal Targets of Trichophyton

Hair, skin, and nails

How is Trichophyton transmitted?

Human to human, animal to human

Name of disease caused by Microsporum

Ringworm of scalp

Ringworm of skin

Principal Targets of Microsporum

Scalp hair

Skin

Not nails

How is Microsporum transmitted?

Animal to human, soil to human, human to human

Name of disease caused by epidermophyton

Ringworm of the groin and nails

Principal targets of epidermophyton

Skin and nails

Not hair

How is epidermophyton transmitted?

Strictly human to human

Zoonoses

Transmission from animal to human

Tinea capitis

Ringworm of the scalp

Affects scalp and hair bearing regions of head; hair may be lost

Tinea barbae

Ringworm of beard

Affects the chin and beard of adult males; contracted mainly from animals

Tinea corporis

Ringworm of Body

Occurs as inflamed, red ring lesions anywhere on smooth skin

Tinea cruris

Ringworm of groin

“Jock itch” affects groin and scrotal regions

Tinea unguium

Ringworm of nails

Persistent colonization of the nails of the hands and feet that distorts the nail bed

Tinea pedis and tinea manuum

Ring worm of foot and hand

Spread by exposure to public surfaces; occurs between digits and on soles

Change socks to prevent fungi growth

Diagnosis for Dermatophytes

Direct microscopic examination and culturing are needed

What are some of the superficial Mycoses?

Tinea versicolor, white piedra, black pierda

What is tinea versicolor caused by?

Malassezia furfur

Tenia versicolor

Elicits mild, chronic scaling, mottling of skin; also implicated in folliculitis, psoriasis, and seborrheic dermatitis

What is white piedra caused by?

Trichosporon beigelii

White piedra

Whitish or colored masses develop scalp, public, or axillary hair

What is black piedra caused by?

Piedraia hortae

Black piedra

Dark-brown to black gritty nodules, mainly in scalp hairs

What are some opportunistic Mycoses?

Candida, aspergillus, cryptococcus

What are some candidas?

Candida Auris and Candida albicans

Candida albicans

Widespread yeast

Candidiasis

Infections can be short lived, superficial skin irritations to overwhelming, fatal systemic diseases

Budding cells of varying size that may form both elongate pseudohyphae and true hyphae

Forms off white last colony with yeasty odor

What are some diseases of Candida albicans?

Vulvovaginal yeast infection, cutaneous candidiasis, thrush

Vulvovaginal yeast infection

Painful inflammatory condition of the female genital region that caused ulceration and discharge

Cutaneous candidiasis

In chronically moist areas of skin and burn patients

Thrush

Thick, white, adherent growth on the mucous membranes of mouth and throat

Diagnosis of Candidiasis

Made if budding yeast cells and pseudohyphae are found; germ tube

Growth on selective, differential media differentiates Candida species

What medication is used for candidiasis?

Nystatin

Nystatin

C. Albicans

Used against diaper rash and thrush

Cryptococcus neoformans

Widespread encapsulated yeast that inhabits soil around pigeon roosts

Cryptococcosis

Common infection of AIDS, cancer, or diabetes patients

Infection of lungs lead to cough, fever, and lung nodules

Dissemination to meninges and brain can cause severe neurological disturbances and death

Pneumocystis jiroveci and Pneumocystis Pneumonia

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

forms secretions in the lungs that block breathing and can be rapidly fatal if not controlled with medication

What disease does aspergillus?

Aspergillosis

Aspergillosis

very common airborne soil fungus

serious opportunistic threat to AIDS, leukemia, and immunodeficient patients

also involved in allergies and toxicoses

Infection of aspergillosis

occurs in lungs; spores germinate in lungs and form fungal balls; can colonize sinuses, ear canals, eyelids, and conjunctiva

Invasive aspergillosis

can produce necrotic pneumonia, and infection of brain, heart, and other organs

Murcomycosis

Also known as Zygomycosis

Zygomycota are extremely abundant saprobic fungi in soil, water, organic debris, and food

usually harmless air contaminants invade the membrane of the nose, eyes, heart, and brain of people with diabetes and malnutrition with severe consequences

What genera is involved in murcomycosis?

rhizopus, absidia, and mucor

common molds on bread

What is the common sources of atopic allergies?

fungal spores

Fungal spores

can cause seasonal allergies and asthma like:

Farmer’s lung, tea picker’s lung, bark stripper’s disease

What can fungal toxins lead to?

mycotoxicoses

mycotoxicoses

caused by ingesting or inhaling fungal toxins

Aflatoxin

toxic and carcinogenic; grains, corn, peanuts; lethal to poultry and livestock

can cause anaphylactic shock

Stachybotrys chartarum

sick building syndrome; severe hematologic and neurological damage

caused by black mold in home