3rd lecture for third year mycosis
By: Dr.Kareema Amine Al-Khafajii, professor ,Department Of
Microbiology, College Of Medicine, University of Babylon.
Mycosis: means fungal diseases .as fungi grow slowly mycosis
may be chronic. Mycosis are classified into the following
categories:
1-The Superficial Mycoses 2-The Cutaneous Mycoses
3-The Subcutaneous Mycoses4-Dimorphic Systemic Mycoses
5-Opportunistic Systemic Mycoses
1-Superficial mycosis: These are superficial cosmetic fungal
infections of the skin or hair shaft. No living tissue is invaded
and there is no cellular response from the host. Essentially no
pathological changes are elicited. These infections are often so
innocuous that patients are often unaware of their condition.
Malassezia infections
Description
Malassezia furfur is the causative agent of Pityriasis versicolor,
Pityriasis folliculitis and it has recently been implicated as a
causative agent of seborrhoeic dermatitis and dandruff. It has
also been recovered in blood cultures from neonate and adult
patients undergoing lipid replacement therapy. M. furfur is a
lipophilic yeast living on the skin as part of the normal flora.
Pityriasis versicolor: This is a chronic, superficial fungal disease
of the skin characterized by well-demarcated white, pink, fawn,
or brownish lesions, often coalescing, and covered with thin
fine scales. The colour varies according to the normal
pigmentation of the patient, exposure of the area to sunlight,
and the severity of the disease. Lesions occur on the trunk,
shoulders and arms, rarely on the neck and face, and fluoresce
a pale yellow or greenish colour under Wood's ultra-violet light.
Young adults are affected most often, but the disease may
occur in childhood and old age.
Diagnosis :depends on clinical picture of the patient, Wood`s
light and, is usually possible by direct microscopic examination
of KOH-treated skin scrapings which show thick-walled round,
budding yeast-like cells and short angular hyphal forms
described as "spaghetti and meatballs." Culture: Culture is only
necessary in cases of suspected fumgaemia.
Management:
The most appropriate antifungal treatment for pityriasis
versicolor is to use a topical imidazole in a solution or lathering
preparation. Ketoconazole shampoo has proven to be very
effective. Alternative treatments include zinc pyrithione
shampoo or selenium sulfide lotion applied daily for 10-14 days
or the use of propylene glycol 50% in water twice daily for 14
days. In severe cases with extensive lesions, or in cases with
lesions resistant to topical treatment or in cases of frequent
relapse oral therapy with either ketoconazole [400 mg single
dose or 200 mg/day for 5-10 days] or itraconazole [200 mg/day
for 5-7 days] is usually effective. Mycologically, yeast cells may
still be seen in skin scrapings for up to 30 days following
treatment, thus patients should be monitored on clinical
grounds. Patients also need to be warned that it may take
many months for their skin pigmentation to return to normal,
even after the infection has been successfully treated. Relapse
is a regular occurrence and prophylactic treatment with a
topical agent once or twice a week is often necessary to avoid
recurrence.
The Cutaneous Mycoses
These are superficial fungal infections of the skin, hair or nails.
No living tissue is invaded, however a variety of pathological
changes occur in the host because of the presence of the
infectious agent and its metabolic products.
Dermatophytosis Description:
Dermatophytosis (tinea or ringworm) of the scalp, glabrous
skin, and nails is caused by a closely related group of fungi
known as dermatophytes which have the ability to utilise
keratin as a nutrient source, i.e. they have a unique enzymatic
capacity [keratinase].
The disease process in dermatophytosis is unique for two
reasons: Firstly, no living tissue is invaded the keratinised
stratum corneum is simply colonised. However, the presence of
the fungus and its metabolic products usually induces an
allergic and inflammatory eczematous response in the host.
The type and severity of the host response is often related to
the species and strain of dermatophyte causing the infection.
Secondly, the dermatophytes are the only fungi that have
evolved a dependency on human or animal infection for the
survival and dissemination of their species.
Clinical manifestations:
The common anthropophilic species are primarily parasitic on
man .They are unable to colonize other animals and they have
no other environmental sources. On the other hand,
geophilic species normally inhabit the soil where they are
believed to decompose keratinaceous debris.
Some species may cause infections in animals and man
following contact with soil. Zoophilic species are primarily
parasitic on animals and infections may be transmitted to
humans following contact with the animal host . Zoophilic
infections usually elicit a strong host response and on the skin
where contact with the infective animal has occurred ie arms,
legs, body or face.
Dermatophytes are found in one of the three genera:
Microsporum: infects only skin + hair . characterized by the
presence of Thick walled Macroconidia , spindle shape with
pointed-end, contains 7-9 cells , with the presence of
microconidia also.
Epidermophyton: infects only skin + nail . characterized by the
presence of Bifurcated hyphae with multiple, smooth, club
shaped macroconidia contains 2-4 cells, with absence of
microconidia.
Trichophyton: infects skin+ hair + nail . . characterized by the
presence of Globose microconidia in grape-like clusters.
Macroconidia are not commonly available but when present,
are cigar-shaped, smooth, thin wall, septate and rounded ends
DERMATOPHYTOSIS: Clinical Classification
Infection is named according to the anatomic location
involved: Tinea manuum (dermatophytes infection of
palmer surface of the hands).
Tinea pedis (athlete's feet: dermatophytes infections of the
feet). Tinea corporis (dermatophytes infection of trunk, neck
and back).Tinea cruris (dermatophytes infection of proximal
medial thighs, perenium and buttocks).Tinea barbae
(dermatophytes infection of hairy skin in the beard area of the
face in adults). Tinea capitis (dermatophytes infection of scalp
usually occurs in children).
Tinea ungium(dermatophytes infection of the nails, commonly
affected house wives and service men).
Subcutaneous Mycoses
Mycetoma (clincal syndrome of localized, indolent, deforming,
swollen lesions and sinuses, involving cutaneous and
subcutaneous tissues, fascia, and bone; usually occurring on
the foot or hand) - etiologic agent may be bacterial or fungi.
Discussion here will be restricted to fungal mycetoma or
eumycetoma.
Chromoblastomycosis (subcutaneous and cutaneous
tissues of the hands and feet).
Phaeohyphomycosis (face, cornea of eye, subcutaneous
and cutaneous part of skin, occasionally cerebral and
systemic).Sporotrichosis (cutaneous and subcutaneous
tissues and adjacent lymphatics that suppurate, ulcerate
and drain).Lobomycosis (subcutaneous and cut. tissues
over different parts of body). Rhinosporidiosis (nasal
cavities, mucocutaneous tissue - rarely it does effect the
vagina, penis, anus, ears, and throat region).
Mycetoma
Mycetoma - clincal syndrome of localized, indolent,
deforming, swollen lesions and sinuses, involving
cutaneous and subcutaneous tissues, fascia, and bone;
usually occurring on the foot or hand) - etiologic agent may
be bacteria or fungi.
one potential causal agent can be Pseudallescheria boydii, a
soil/water inhabiting fungus with worldwide distribution.
However other fungi can be involved.
Fungi associated with fungal mycetoma are opportunistic.
mycotic mycetoma - usually more common in men (3:1 to 5:1)
than in women usually results from trauma or puncture
wounds to feet, legs, arms and hands (usually on the feet)
starts out as tumor-like to subcutaneous swelling ruptures near
the surface; infects deeper tissues including subcutaneous
tissues and ligaments (tendons, muscles and bone are usually
spared)small particles or grains leak out of the lesions - these
represent the to yellowish microcolonies.
lesions of mycetoma seldom heal spontaneously disease is
chronic may continue for 40-50 years.
Treatment:
P. boydii is resistant to all systemically useful drugs, including
amphotericin B, KI, 5-fluorocytosine, 2-hydroxystilbamidine
ketoconazole appears to be ineffective in clinical trials
intravenous miconazole (9 mg per Kg of body weight
sometimes higher doses) shows promise ,surgery and removal
of tumor ( if small it is encapsulate, if larger amputation my be
required),Combining miconazole and surgery may prove useful
in effectively treating the disease.
Chromoblastomycosis - chromomycosis or verrucous
dermatitis
Disease is one of hyperplasia, characterized by the formation of
verrucoid (rough), warty, cutaneous nodules, which may be
raised 1-3 cm above the skin surface. The roughened, irregular,
pedunculated vegetations often resembles the florets of
cauliflower.
This disease is caused by Fonsecaea pedrosoi and Phialophora
verrucosa (identical to Cadophora americana which causes
bluing of lumber), both of which are dematiaceous fungi (darkly
pigmented) occurs rarely in animals (such as, horses, cats, dogs,
and frogs)
soil-inhabiting fungi susceptibility enhanced by going barefoot
or wearing sandals found almost exclusively in laborers enters
hand or feet after trauma found primarily in the tropics or
subtropics, dull red or violet color on skin may resemble a
ringworm lesion develops into a verrucous lesion ,pruritus
(itchiness) and papules may develop fungus gets under the skin
(produces bumps),bumps may block lymphatic system and
cause elephantiasis sometimes bacterial infection may enter
and cause a secondary infection rarely this fungus spreads to
other areas of the subcutaneous tissue. potentially may spread
to brain (life-threatening in that case).biopsy tissue - look at the
skin for fungus hematoxylin stain - look for fungal cells
scattered among skin cells attempt to culture fungus from
biopsy tissue must always take place to identify the etiological
or causal agent colonies of fungi are dark or blackish Two
species implicated in this mycosis - each may produce several
spore types Fonsecaea pedrosoi - Cladosporium type and
Rhinocladiella type of conidiation Phialalophora verrucosa Phialophora type (flowers in the vase conidiation) fungi found
growing on plant debris, wood, soil.
Treatment
usually not fatal or necessarily painful unsightly
diseasethiabendazole ,shows promise (given orally and
on skin mixed with dimethyl sulfoxide [DMSO] - to
deliver drug) - experimental drug
surgical excision, electrodesiccation, or cryosurgery are useful
in early stages of disease
application of heat to infect site has been reported to effect a
cure of the disease after six months of treatment (using pocket
warmers)
itraconazole shows promise in clinical trials.
For trial studies using posaconazole therapy check the following
link at:
(dimorphic fungi( Systemic Infections by True Pathogens
Histoplasma capsulatum
Coccidioides immitis
Blastomyces dermatitidis
Paracoccidioides brasiliensis
Histoplasmosis: Ohio Valley Fever
Histoplasma capsulatum – most common true pathogen; causes
histoplasmosis Typically dimorphic Distributed worldwide, most
prevalent in eastern and central regions of US Grows in moist soil high in
nitrogen content Inhaled conidia produce primary pulmonary infection
that may progress to systemic involvement of a variety of organs and
chronic lung disease. Amphotericin B, ketoconazole.
Coccidioidomycosis: Valley Fever
Coccidioides immitis - causes coccidioidomycosis .Distinctive
morphology – blocklike arthroconidia in the free-living stage
and spherules containing endospores in the lungs lives in
alkaline soils in semiarid, hot climates and is endemic to
southwestern U.S. Arthrospores inhaled from dust, creates
spherules and nodules in the lungs. Amphotericin B treatment.
Blastomyces dermatitidis: North American Blastomycosis
Blastomyces dermatitidis- causes blastomycosis Dimorphic
Free-living species distributed in soil of a large section of the
midwestern and southeastern U.S.Inhaled 10-100 conidia
convert to yeasts and multiply in lungs,Symptoms include
cough and fever.Chronic cutaneous, bone, and nervous system
complications. Amphotericin B.
Paracoccidioidomycosis
Paracoccidioides brasiliensis Distributed in Central and South
America .Lung infection occurs through inhalation or
inoculation of spores.Systemic disease is not common.
Ketoconazole, amphotericin B, sulfa drugs.
Opportunistic Mycoses
Most important fungal pathogens:
Aspergillus , Candida,Cryptococcus ,Pneumocystis ,Rhizopus
Mucor, Absidia.
Infections by Candida: Candidiasis.Candida albicans
.Widespread yeast.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, pasty colony
with a yeasty odor.
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 and throat
Vulvovaginal yeast infection – painful inflammatory condition
of the female genital region that causes ulceration and whitish
discharge
Cutaneous candidiasis – occurs in chronically moist areas of
skin and in burn patients.
Diagnosis and Treatment
Presumptive diagnosis made if budding yeast cells and
pseudohyphae are found; germ tube .Growth on selective,
differential media differentiates Candida species
Topical antifungals for superficial infections, amphotericin B
and fluconazole for systemic.
Cryptococcosis and Cryptococcus neoformans
Cryptococcus neoformans causes cryptococcosis.
A widespread encapsulated yeast that inhabits soil around
pigeon roosts.Common infection of AIDS, cancer or diabetes
patients.Infection of lungs leads to cough, fever, and lung
nodules. Dissemination to meninges and brain can cause severe
neurological disturbance and death.
Diagnosis and Treatment
Negative stain demonstrating encapsulated budding yeast
Biochemical tests, serological testing.Systemic infection
requires amphotericin B and fluconazole.
Pneumocystis (carinii) jiroveci and Pneumocystis Pneumonia
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 and can be rapidly fatal if not controlled with
medication.Pentamidine and cotrimoxazole.
Aspergillosis: Diseases of the Genus Aspergillus
Very common airborne soil fungus. 600 species, 8 involved in
human disease; A. fumigatus most commonly.Serious
opportunistic threat to AIDS, leukemia, and transplant
patients.Infection usually 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. Amphotericin B and nystatin.
Zygomycosis
Zygomycota are extremely abundant saprobic fungi found in
soil, water, organic debris, and food.Genera most often
involved are Rhizopus, Absidia, and Mucor. Usually harmless air
contaminants invade the membranes of the nose, eyes, heart,
and brain of people with diabetes and malnutrition, with severe
consequences.
Miscellaneous Opportunists
Any fungus can be implicated in infections when immune
defenses are severely compromised.Geotrichum candidum –
geotrichosis; mold found in soil, dairy products; primarily
involved in secondary lung infections Fusarium species – soil;
occasionally infects eyes, toenails, burned skin.
Fungal Allergies and Intoxications
Fungal spores are common sources of atopic allergies.
Seasonal allergies and asthma.farmer’s lung, teapicker’s lung,
bark stripper’s disease. Fungal toxins lead to mycotoxicoses
usually caused by eating poisonous or hallucinogenic
mushrooms.
aflatoxin toxic and carcinogenic; grains, corn peanuts; lethal to
poultry and livestock. Stachybotrys chartarum – sick building
syndrome; severe hematologic and neurological damage.
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