2. General Characteristics
• Dermatophytes are cutaneous fungi which infect only
the keratinized tissues by liberting keratinase enzyme
which helps them to invade into keratinized tissue
like stratum corneum layer of skin, hair and nail.
• It is a group of about 40 related fungi that belong to
three genra : 1. Microsporum
2. Trichophyton
3. Epidermophyton.
• They are restricted to non-viable skin because most
are unable to grow at 37˚C or in the presence of
serum .
3. • Many species have particular keratinase, elastase and
other enzymes which make them host specific.
• Several are capale of sexual reproduction – produce
ascospore. Thus belongs to genus Arthroderma.
Ascospore (sexual spores)
4. • In skin, they produce hyaline, septate, branching
hyphae, or chains of arthoconidia.
• E. floccosum is the only pathogen in this genus which
produces macroconidia.
Arthroconidia (asexual form)
5. • They are highly contagious and frequently
transmitted by exposure to shed skin scale, nails,
hairs cantaing hypae and conidia.
• They remail viable for long periods on fomites.
6. Classification
• According to shape and site of infection:
1. Microsporum : spindle shaped; infect skin and hair.
- M. canis
- M. gypseum
- M. gallinae
- M. nanum.
2. Trichophyton : pencil shaped; infect skin, nail, hair.
- T. rubrum
- T. tonsurans
- T. mentagrophytes.
7. 3. Epidermophyton : club shaped; infect skin and nail.
- E. floccosum.
• According to habitat :
1. Antropophilic : habitat in human body.
- some Trichophyton species
- E. floccosum.
2. Geophilic : usually habitat in soil.
- M. gypseum.
8. 3. Zoophilic : usually habitat in animal.
- M. canis (dogs and cats)
- M. gallinae (fowl)
- M. nanum (pigs)
- T. equinum (horses)
- T. verrucosum (cattle).
9. Immunity
• Trichophytid reaction : trichophytin is a crude antigen
preparation that can be used to detect immediate or delayed type
hypersensitivity.
- chronic, noninflammatory dermatophyte infection
poor cell mediated immune response to dermatophyte antigen.
Immediate type hypersensitivity with elevated IgE.
Allergic reaction- dermatophytid (usuallly vesicle and often in
hand)
Trichophytid reaction : markedly positive
10. Clinical findings
• Dermatophytosis is classified according to site of
involvement :
1. Tinea capitis : infection in scalp and hair.
2. Tinea barbae : infection in beard area.
3. Tinea corporis : infection in the trunk.
4. Tinea cruris (jock itch): infection in groin/ inguinal
region.
5. Tinea manum : infection in hand.
6. Tinea unguium (onychomycosis): infection in nail.
7. Tinea pedis (athlete’s foot) : infection in foot.
11. • Tinea Capitis :
- Dermatophytosis or ringworm of the scalp and hair is called
Tinea capitis.
- Caused by Trichophyton or Microsporum.
- Pathogenesis :
Hyphal invasion of the skin of scalp
Subsequent spread down the keratinized wall of hair follicle
Infection begins just above hair follicle, grow downwards on
noninvolving area as the hair grows upwards.
Production of dull grey, circular patches of
alopecia, scaling and itching.
12. As the hair grows out of the follicle--
1.Microsporum : Hypae produce chain of spores
forming sheath around the hair shaft- ectothrix.
2. Trichophyton : hypae produce spores within the hair
shaft - endothrix.
- Hair become weakened; typically break easily at the
follicle opening.
A- ectothrix; B endothrix
13. 3. Zoophilic species : induce combined inflammatory
and hypersensitivity reaction – kerion.
4. Trochophyton schoenleinii : acute inflammatory
reation of hair follicle leading to formation of scutula
(crust)- favus.
14. • Tinea Barbae: highly inflammatory reaction
resembling pyogenic infecion.
• Tinea Corporis : annular lesion of ringworm with a
clearing, scaly center surrounded by a red advancing
border that may be dry or vescicle.
15. - Pathogenesis :
Fungal metabolites, enzymes, antigens diffuse through
the viable layers of the epidermis
Erythema, vesicle formation, pruritus
Lesion expand centrifugally and active hyphal growth at
periphery.
16. • Tinea cruris : mostly occurs in men.
- dry, itchy lesions often start at the scrotam and
spread to the groin.
• Tinea manus : dry, scaly lesion may involve one or
both hands, single finger, or two or more fingers.
17. • Tinea Unguium / Onychomycosis :
- May affect toe nails or finger nails, but toe nail
infection is particularly common which follows tinea
pedis.
- Caused by : Trichophyton and Epidermophyton.
- Risk factors :
1. Diminished blood supply.
2. Humid, moist environment.
3. Perspiring heavily.
4. Bare foot in dump places.
5. DM, immunosuppression.
18. - Pathogenesis :
With hyphal invasion
Nails become yellow, brittle, thickened and crumbly.
19. • Tinea Pedis / Athlete’s foot :
- Chronic infection of toe webs. May be vesicle,
ulcerative and moccasin types, hyperkeratosis of the
sole.
20. • Coarse of disease :
Itching between toes.
Development of small vesicles.
Rupture of vesicle and discharge of a thin fluid.
Skin of the toe webs become macerated and peels.
Cracks appear and secondary bacterial infection develops.
When become chonic- peeling and cracking are
accompanied by pain and pruritus.
21. Laboratory diagnosis
• Sample :
1. Skin scrapping.
2. Nail scrapping.
3. Hair plucking.
• Collection of samples :
1. Skin : from the margin of the lesion, with the
scalpel.
2. Nail : deeper part is collected and superficial part is
discarded.
3. Hair : plucked by fine forceps.
22. • Wood’s lamp test :
ectothrix of Microsporum species impart a greenish
to silvery fluerescence when examined under Wood’s
light.
23. • Microscopic examination :
1. KOH preparation of skin or nail : branching hypae
or chains of arthoconidia are seen.
Unstained microscopic
KOH prep. of scraping from
a ring worm showing
arthrospore (asexual spores).
24. Multicellular macroconidia
with echinulate wall of M.
canis
Club shaped
macroconidia
with thin and
smooth wall
arise in small
clusters of E.
floccosum.
Small and
piriform
microconidia of
T. rubrum
Elongated microconidia of T.
tonsurans
Abundant grape
like clusters of
spherical
microconidia on
terminal branch
of T.
mentagrophytes.
25. 2. KOH preparation of hair : ectothrix and endothrix are
seen.
Left - ectothrix (arthospore outside hair shaft);
Right – endothrix (arthospore inside hair shaft.)
26. • Culture :
- Incubation period : 1-3 weeks.
- Incubation temparature : 25˚ C.
- Media used :
1. Sabouraud’s dextrose agar media.
2. Dermatophyte test media : Sabouraud’s dextrose
agar + cyclohexamide + chloramphenicol + phenol
red.
3. Malt agar.
- Colony morphology :
27. T. rubrum : White cottony
surface and a deep red
nondiffusible pigment from
reverse side
T. tonsurans : flat, powdery,
velvety colony.
T. metagrophytes : cottony
to granular colony
Microsporum : white cottony
sarface with deep yellow from
revese.
Epidermophyton : flat, velvety
with a tan to olive green tinge.
Dermatophyte test media
28. • Others :
1. PCR : species specific identification.
2. Nutritional test and growth at 37˚ C.
3. In vitro hair perforation : placing an organism in a
petri dish- water, yeast extract, hair.
29. Treatment
• Therapy consists of thorough removal of infected and dead
epithelial structures and application of a topical antifungal drug.
1. Tinea capitis :
- oral Griseofulvin or terbinafin several weeks.
- topical shampoo and miconazole cream several weeks.
- alternative : itraconazole, ketokonazole.
2. Others :
- oral itraconazole and terbinafine.
- topical miconazole, tolnafate, clotrimazole 2-4 weeks.
- troublesome cases : oral griseofulvin.
3. Tinea unguium :
- orat itraconazole or terbinafine for months with surgical removal
of the nail.
- topical imidazole, luciconazole,.
