Transcript of Mrs. Dalia Kamal Eldien Msc in microbiology. Introduction Dermatophytosis is a common contagious...
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- Mrs. Dalia Kamal Eldien Msc in microbiology
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- Introduction Dermatophytosis is a common contagious disease i.e
infectious disease caused by fungi known as dermatophytes.
Dermatophytes belong to Deuteromycetes class Dermatophytes a group
of organisms that are able to breakdown the keratin in tissues such
as the epidermis, hair, nails, feathers, horns and hooves. Most of
these fungi reside in the soil and are involved in
decomposition.
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- Some dermatophytes anthropophilic species, are adapted to
humans, and are usually transmitted from person to person. Others
zoophilic species, are adapted to animals, but can transmite to
human. A few geophilic species, normally live in the environment,
but occasionally act as parasites.
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- Etiology Dermatophytes have 3 genera and many species
1-Microsporum : affect mainly skin and hair, common species include
o M. gypseum o M. canis (Zoophilic ) o M. audouinii o M. nanum
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- 2-Trichophyton : affect skin, hair & nail common species
include. o T. tonsurans o T. rubrum o T. violaceum o T.
mentagrophytes o T. interdigitale o T. soudanense o T. schoenleinii
3- Epidermophyton. affect Skin, nail the species is o E.
floccosum
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- Dermatophytes grow best in warm and humid environments and
therefore more common in tropical and subtropical regions. Their
distribution varies with the organism. M. canis, M. nanum, M.
gypseum, T. mentagrophytes, T. verrucosum and T. equinum, occur
worldwide Epidemiology
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- morphology Microsporum : produce many macro conidia(large,
spindle shape& multicellular), and few microconidia M. canis :
have special spicules M. audunii : produce special structure refer
as the pictenate body Trychophyton: produce many micro conidia and
few macroconidia (thin wall, cigar shape) T. mentagrophytes :
produce the spiral hyphae T. schoenleinii : produce special
structure refer as the favic chandler Epidemphyton: produce many
macro(large, multi cellular & club shape) but no micro
conidia
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- Microsporum canis macroconidia with spicules
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- Microsporum gypseum macroconidia
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- Microsporum audouinii (pectinate bodies)
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- Trichophyton spp(examine the macro and micro conidia)
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- Trichophyton mentagrophytes(spiral hyphe)
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- E.floccosum macroconidia
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- Transmission People and animals become infected by
dermatophytes after contact with spores (conidia). Incubation
Period The incubation period in humans is usually 1 to 2 weeks.
Clinical Signs The symptoms of dermatophytosis vary, depending on
the infecting organism, affected tissues (e.g., skin, hair or
nails) and area of the body. In unhaired (glabrous) skin, the
lesions are usually characterized by inflammation that is most
severe at the edges, with erythema, scaling and occasionally
blister formation. The central area may clear, resulting in the
formation of a classic ringworm lesion.
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- Ringworm lesion
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- In haired areas, the hairs become brittle and areas of alopecia
may appear. Infection begins in a growing hair or in the stratum
corneum, where threadlike hyphae develop from the infective
arthrospores or fungal hyphal elements. Hyphae can penetrate the
hair shaft and weaken it, which, together with follicular
inflammation, leads to a common clinical sign of patchy hair loss.
As the infection matures, clusters of arthro spores develop on the
outer surface of infected hair shafts. Broken hairs infected with
spores are important sources for spread of the disease.
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- Tinea capitis
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- In humans, dermatophytoses are referred to as tinea infections,
and are named according to the area of the body involved. Tinea
capitis : most often seen in children, is a dermatophyte infection
of the hair and scalp. Tinea barbae in the beard and mustache area
Tinea corporis occurs on the trunk and extremities Tinea cruris
infection of the groin Tinea pedis (athletes foot) is an infection
of the foot Tinea unguium (or onchomycosis) is infection of the
nails, finger or toe Tinea manuum hand and interdigetal space
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- Lab diagnosis Specimen Before collect the specimen disinfect
the area with 70% alcohol with a pieces of gauze, using sterile
blunted scalpel collect the specimen. Skin scrapings should be
taken from the edge of the lesion onto folded black paper. Hairs
should be plucked (not cut) from this area, the best hairs to
select are those that fluoresce under a Wood's lamp, or are broken
or scaly. Nail scrapings are generally taken from the nail bed, or
from deeper portions of the nail after removing the outer layers
(except in cases where the infection is entirely superficial).
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- Wood's lamp examination
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- Direct microscopy Is a most important diagnostic step Using 20%
KOH, in clean slide add one drop, to it take part of specimen,
passing 3 times over BB to and allowed to clear for 30 to 60
minutes to clear the keriatine and expose the fugal elements,
before examining on a light or phase contrast microscope.
Fluorescence microscopy, using calcofluor white or other stains,
can also be used to visualize dermatophyte structures.
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- Under the microscope :- Skin: epithelia cell, if positive see
the segmented hyphae, Hyphae rounding up into arthroconidia are
diagnostic, but hyphae alone could be caused by other fungi,
including contaminants. Nail: the same picture but the epithelial
more flattened Hair: arthroconidia may be found outside (ectothrix)
or inside (endothrix) the hair shaft.
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- KOH mount of infected skin scales (left) and nail material
(right) showing typical dermatophyte hyphae breaking up into
arthroconidia.
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- Ectothrix spore(right)& Endothrixspore(left)
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- Culture : Fungal cultures, which identify the species of
dermatophyte, also be necessary if the diagnosis is uncertain, or
the infection is resistant to standard treatment. Specimens should
be inoculated onto primary isolation media, like Sabouraud's
dextrose agar containing cycloheximide (actidione) and
chloramphnicol, incubated at 26-28C for 4 weeks. Nails are scraped
or minced into small pieces Hair is cut into short segments Each
specimen is divided between at least two types of culture
media
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- Potato dextrose agar: is a media useful for the production of
pigment Bromocresol purple milk solids glucose: is a differential
media useful in the characterization of dermatophyte species. The
growth pattern of restricted or profuse is determined by comparison
to a tube of nutrient media such as SDA. Some species produce an
alkaline reaction (change media to purple), others do not produce a
pH change (leave the media a sky blue color). Hydrolysis of the
milk solids results in a zone of clearing around the colony.
Colonies appear in 5 days to 4 weeks, depending on the organism.
Colony morphology can differ with the medium. Descriptions are
usually based on Sabouraud agar
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- Colonies of T. mentagrophytes (left), T. rubrum (center) and T.
violaceum (right) showing differential responses on Bromocresol
Purple Milk Solids Glucose agar. T. mentagrophytes shows
unrestricted growth with alkaline (purple) color change, T. rubrum
shows restricted growth with no pH change, and T. violaceum
produces weak growth accompanied by clearing of the milk solids and
a purple color change.
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- Dermatophyte species can be identified by the colonial
morphology. Microscopical exam: to examine the appearance of
microconidia, macroconidia and other microscopic structures
Biochemical characteristics such as urease production; and
nutritional requirements. Specialized tests such as the ability to
penetrate hairs in vitro, or mating tests (which are usually
available only at reference laboratories)
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- Mixed culture of T. violaceum and T. tonsurans from a case of
endothrix Tinea capitis
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- M. gypseum culture
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- T.schoenleinii
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- M.canis
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- Some dermatophytes fluoresce when they are stimulated by the
wavelengths of ultraviolet (UV) light in a Woods lamp. Histology
(biopsy) is occasionally helpful, especially in deep mycoses and
some infections of the nails. The organisms are visualized best
with periodic acidSchiff (PAS) staining, although they may also be
found in hematoxylin-eosin stained preparations. PCR tests have
been published for a number of organisms, and molecular methods of
diagnosis might become more common in the future.
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- Treatment Dermatophyte infections are treated with a variety of
topical and oral antifungal drugs. Topical agents are ineffective
against organisms that infect the hairs. These infections are
usually treated with systemic antifungals, although topical lotions
or shampoos are sometimes used concurrently to decrease shedding of
fungi and spores.
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