This document discusses dermatophytes, which are fungi that can infect the skin, hair, and nails. It describes the three main genera (Trichophyton, Microsporum, Epidermophyton) and how they are classified based on their sources (animal, human, soil). Common sites of dermatophyte infections are also summarized, such as tinea pedis (athlete's foot), tinea cruris (jock itch), and tinea capitis (scalp ringworm). Laboratory diagnosis involves microscopic examination of skin or hair samples in potassium hydroxide, as well as fungal culture.

1. Dermatophytes
Dr Margaret Lubwama

2. How do you group fungi?
Phylum
Basidiomycota
Ascomycota
Zygomycota
Organism
Yeast
Dimorphic fungi
Mold
Syndrome
Disseminated infection
Opportunistic infection
Subcutaneous infection
Superficial infection
Dermatophytes

4. Ascomycota

5. Ascomycota

7. Dermatophytoses
• The dermatophytes are molds that can invade the
stratum corneum of the skin or other keratinized
tissues derived from epidermis, such as hair and
nails
• They may cause infections (dermatophytoses) at
most skin sites, although the feet, groin, scalp,
and nails are most affected
• The dermatophytes are among the earliest
microorganisms that were found to cause
infections in humans

8. The Dermatophytes
• There are three genera of pathogenic dermatophyte
fungi—Trichophyton, Microsporum, and
Epidermophyton. The last genus is represented by only
a single species, Epidermophyton floccosum
• These keratinophilic organisms probably arose as
saprophytic soil fungi
• zoophilic, anthropophilic, or geophilic, depending on
whether their primary source is an animal, human, or
soil, respectively
• most clinical isolates are imperfect fungi, organisms
that do not produce sexual structures in culture-
complicates taxonomy

9. Classification of the Main Dermatophytes
(Trichophyton, Microsporum, and Epidermophyton)
Anthropophilic Geophilic
Zoophilic
Organism Sources
Trichophyton
concentricum
Trichophyton ajelloi Trichophyton erinacei * Hedgehogs
T. gourvilii T. terrestre T. equinum Horses
T. mentagrophytes
interdigitale *
Microsporum fulvum T. mentagrophytes
mentagrophytes
Rodents
T. megnini M. gypseum T. quinckeanum Mice
T. rubrum T. simii Monkeys
T. schoenleinii T. verrucosum Cattle
T. soudanense Microsporum canis Cats, dogs
T. tonsurans M. gallinae Chickens
T. violaceum M. nanum Pigs
T. yaoundei M. persicolor Bank voles
Microsporum audouinii
M. ferrugineum
Epidermophyton floccosum

10. Pathogenesis
• Transfer of infecting organisms from soil, other
animals, or humans is accomplished by means of
arthrospores, which are vegetative cells with thickened
cell walls formed by dermatophyte hyphae
• adherence of fungal cells to keratinocytes
• germination leads to invasion
• invasion of the skin
• Children: low composition of inhibitory fatty acids in
sebum
• After invasion, dermatophytes secrete proteinases such
as zinc-containing metalloproteinases, which aid
penetration

12. Virulence factors of dermatophytes
Virulence factor Description and function
Subtilisin-like proteases (Sub) Endoprotease activity in keratin digestion.
Reported as allergens and involved in immune
response induction
Fungalysin-like Metalloproteases
(Mep)
Endoprotease activity in keratin digestion
Leucinaminopeptidases (Lap) Exoprotease activity in keratin digestion.
Dipeptidyl peptidases (Dpp) Exoprotease activity in keratin digestion.
Secondary metabolite production
associated enzymes
Polyketide synthase and non-ribosomal peptide
synthetase
Cysteine dioxygenases Sulfitolysis of keratin. Involved in triggering humoral
immune response during infection.
Hydrophobins Hydrophobin rodlet layer on conidial surface.
Related to avoiding immune recognition by
neutrophils
LysM proteins Protein domains related to binding to skin
glycoproteins. Possibly involved in immune evasion.
Heat shock proteins Hsp 30, Hsp60, Hsp70. Associated with adaptation
to human temperature, keratin digestion.
Other hydrolases and cell wall
remodeling-associated enzymes
Lipases, glucanases, chitinases, betaglusidases,
mannosyl transferases. Many involved in triggering
humoral immune response during infection

13. Clinical features
• annular scaling patch with a raised margin
showing a variable degree of inflammation, the
center usually being less inflamed than the edge
• The word tinea is used to refer to dermatophyte
infections, and it is usually followed by the Latin
description of the appropriate site
Hence, tinea pedis is an infection of the feet and
tinea capitis, the scalp

14. Clinical features
• The clinical appearances of the infection vary with the
site, the fungal species involved, and the host’s
immune response. Zoophilic fungi often cause
inflammatory lesions, and in some cases large pustular
lesions (kerions) may develop. By contrast, lesions
caused by anthropophilic dermatophytes often show
little inflammation and may become chronic
• Dermatophytes cause infections irrespective of the
patient’s underlying immune status. However, in
common with other infections, the clinical appearances
are altered in immunocompromised individuals.
Dermatophyte lesions are usually less inflamed in
patients with diseases affecting T-lymphocyte function

15. Tinea pedis
• T. rubrum or T. mentagrophytes (interdigitale), less commonly by E.
floccosum
• The infection usually starts in the lateral interdigital spaces of the
foot or on the undersurface of the lateral aspects of the toes
• The main symptom is itching, although this is variable
• The skin usually cracks and may become severely macerated
• The infection may also spread onto the dorsum of the feet, usually
on the lateral side of the foot
• Blisters may also be formed in small clusters on the sole
• Complications: bacterial cellulitis and fungal invasion of the toenails
(onychomycosis) or the skin of the dorsum of the foot and leg
• Scaling between the toes is often referred to as athlete’s foot

16. Tinea cruris
• groin infections: T. rubrum and E. floccosum (jock itch)
• starts with scaling and irritation in the groin. The rash
usually involves the anterior aspect of the thighs, less
commonly the scrotum. The leading edge extending
onto the thighs is prominent and may contain follicular
papules and pustule
• Candidiasis of the groin may also mimic tinea cruris,
but an important clue to the presence of Candida is the
appearance of small satellite pustules beyond the free
margin of the rash

17. Tinea corporis
• Most lesions have a prominent edge that may contain pustules or
follicular papules, and the center of the lesion is often less inflamed
and scaly
• Sites commonly involved are the trunk and legs. Itching is variable,
and lesions may be single or multiple
• infections caused by anthropophilic dermatophytes such as T.
rubrum are less inflammatory and less clearly demarcated, and in
some patients it is necessary to search for the margin carefully to
delineate the rash. Lesions are usually hyperpigmented in
pigmented skins
• zoophilic infections such as those caused by M. canis and T.
verrucosum are more inflammatory, and lesions may become
elevated and contain pustules. Infections caused by M. gypseum are
also usually inflammatory and may have a brick-red appearance

18. Tinea Capitis
• Endemic infections associated with anthropophilic
organisms, and sporadic disease with zoophilic fungi
• classified by the pattern of hair shaft invasion.
Dermatophyte infections in which arthrospores are formed
on the outside of the hair shaft are known as ectothrix
infections and those in which the spores develop within the
hair itself as endothrix infections
• The main clinical feature of dermatophyte scalp infections
are the appearance of scaling of the scalp skin that is
associated with a variable degree of erythema and
inflammation and alopecia
• The infection is often accompanied by itching. A
pathognomonic feature is hair loss

19. Others
• Dermatophytosis of Hand (Tinea Manuum)
• Dermatophytosis of face (Tinea Faciei)
• Dermatophytosis of neck and beard area
(Tinea barbae)

20. Onychomycosis Caused by Dermatophytes
• Onychomycosis, or fungal infection of the nails, usually
occurs in individuals with infections of adjacent toe or
palmar skin, except in rare cases of childhood nail
infection in which nail plate invasion may develop
without skin involvement
• The most common clinical pattern of onychomycosis is
distal and subungual onychomycosis, in which the nail
plate is invaded from the distal and lateral borders
• The most common cause of onychomycosis is T.
rubrum, which often accompanies long-standing
disease, and the infection involves the entire nail plate.

21. Deep Dermatophyte Infections
• On rare occasions patients known to be
immunocompromised develop dermatophyte infections in
which the fungi invade subcutaneous tissues via the
lymphatics, usually causing clusters of granulomas,
lymphedema, and draining sinuses
• Sometimes aggregates of fungal hyphae resembling those
found in eumycetomas may be seen in histologic sections.
These dermatophyte “pseudomycetoma” grains may be
surrounded by neutrophil abscesses, but often the fungal
hyphae are engulfed by giant cells in tissue sections
• Deep dermatophyte infections may extend further to
involve draining lymph nodes or other sites, including the
liver and brain, and they may be fatal

23. Laboratory diagnosis
• In some cases it is possible to screen patients
with scalp infections by using a filtered
ultraviolet light source (Wood’s light)
• Fluorescent hairs are infected, and apart from
its use as a screening procedure, Wood’s light
examination may be helpful as a method of
selecting hairs for microscopy and culture

24. Laboratory diagnosis
• The laboratory diagnosis of dermatophytosis
depends on the examination and culture of
scrapings or clippings from lesions
• Material should be allowed to soften in 10%
to 20% potassium hydroxide before being
examined under the microscope
• Fungal hyphae can be seen as chains of
arthrospores in cleared scales or clippings

25. Laboratory diagnosis
• Dermatophytes infecting hair
show characteristic
appearances that are helpful
in recognition
• ectothrix infections: Most of
the pathogenic Microsporum
spp., T. verrucosum, produce
large arthrospores
• Endothrix infections: majority
of Trichophyton spp.
• T. schoenleinii invades hair, but
hyphae regress and leave
airspaces within the hair shaft

26. Laboratory diagnosis
• Culture: Primary isolation is carried out at room
temperature, usually on Sabouraud’s agar containing
antibiotics (penicillin-streptomycin or choramphenicol) and
cycloheximide (Acti-Dione), an antifungal agent that
suppresses the growth of environmental contaminant fungi
• Most dermatophytes can be identified within 2 weeks
• Lactophenol cotton blue wet mount
• Identification depends on the gross colonial and
microscopic morphology: colony pigmentation, texture, and
growth rate and distinctive morphological structures, such
as microconidia, macroconidia, spirals, pectinate branches,
pedicels, and nodular organs

28. Treatment
Dermatophytosis, Clinical Disease Pattern Treatment
Tinea pedis
Interdigital Topical cream/ointment: terbinafine, imidazoles (miconazole,
econazole, clotrimazole, etc.), undecenoic acid, tolnaftate
“Dry type” Oral: terbinafine 250 mg/day for 2–4 weeks, itraconazole 400 mg/day
for 1 week per month (repeated if necessary), fluconazole 200 mg
weekly for 4–8 weeks
Tinea corporis
Small, well-defined lesions Topical cream/ointment: terbinafine, imidazoles (miconazole,
econazole, clotrimazole, etc.)
Larger lesions Oral: terbinafine 250 mg/day for 2 weeks, itraconazole 200 mg/day for
1 week, fluconazole 250 mg weekly for 2–4 weeks
Tinea capitis Griseofulvin: 10–20 mg/kg daily for minimum 6 weeks
Terbinafine: < 20 kg: 62.5 mg/day; 20–40 kg: 125 mg/day; > 40 kg:
250 mg/day
Itraconazole: 4–6 mg/kg pulsed dose weekly
Fluconazole: 3–8 mg/kg pulsed dose weekly
Onychomycosis Terbinafine: 250 mg daily for 6 weeks
Fingernails Itraconazole: 400 mg/day for 1 week each month, repeated for 2–3
months
Fluconazole: 200 mg weekly for 8–16 weeks
Toenails Terbinafine: 250 mg daily for 12 weeks
Itraconazole: 400 mg/day for 1 week each month, repeated for 2–4
months
Fluconazole: 200 mg weekly for 12–24 weeks