Dermatophytoses

 Superficial mycoses are of three types

           1. Surface Infections

• Pityriasis versicolor (Tinea versicolor)- Pityrosporum orbiculare/Malassezia spp.- M. furfur
• Tinea nigra- Cladosporium werneckii/Hortaea werneckii
• Piedra -    Piedra hortae (black)/ Trichosporon beigelii (white)

2. Cutaneous Infections - Dermatophytoses

            3. Candidiosis - Candida

Dermatophytoses 

• Dermatophytes –closely related species of filamentous fungi- infect only superficial keratinized tissues- nails, hair, and skin

• Also called Tinea/"ringworm" disease - called ‘herpes' by the Greeks, and ‘tinea' by the Romans (means small insect larvae).

• Three important genera, (i.e., Microsporum, Trichophyton and Epidermophyton) – 40 species identified
• Severity of disease depends on (1) strains or species of fungus involved and (2) sensitivity of the host to a particular pathogenic fungus. 
• More severe reactions occur when a dermatophyte infects non-hosts (e.g., from an animal species to man).

Common Causative agents:

a. Microsporum - hair, skin, rarely nails - children, rarely in adults - spontaneous remission

b. Trichophyton - hair, skin & nails - both children & adults - chronic.

c. Epidermophyton - skin, nails, rarely hair - adults, rarely children

• In lesions, dermatophytes appear as hyphae and arthrospores
• Cultures on SDA show characteristic colonies with septate hyphae and two types of asexual spores , microconidia and macroconidia. 
• Differentiation into three genera is based on the nature of microconidia
  
  
  

Trichophyton

• Colonies powdery, velvety or waxy with pigmentation (on the back side) characteristic of different species
• Microconidia abundant, arranged in clusters along the hyphae or borne on conidiophores
• Macroconidia scanty in number-elongated with blunt ends
• Macroconidia have distinctive shapes for different species-important in species identification
  
• Special hyphal characters like spiral hyphae, racquet mycelium and favic chandeliers
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• Areas affected: hair, skin and nails
• Trichophyton rubrum – most common species infecting human beings-causes chromic, treatment resistant lesions
  
  
  
  
  
  

Microsporum

·         Colonies are cottony, velvety or powdery, with white to brown pigmentation

·         Microconidia are relatively scanty and are not distinctive

·         Macroconidia are abundant-large, multicellular, spindle-shaped structures, borne singly on the ends of hyphae

·         Microsporum species infect the hair and skin but usually not the nails

·         Microsporum gypseum, Microsporum canis

 Epidermophyton

·         Colonies are powdery and greenish yellow on the reverse

·         Microconidia absent; Macroconidia are multicellular, pear (club) shaped and typically arranged in clusters

·         Epidermophyton attacks the skin and nails but not the hair-

·         Epidermophyton floccosum - Only one pathogenic species in this genus.

Pathogenicity

• Dermatophytes grow on the dermis and its appendages (hair follicles and nails) 
• Keratinophilic - "keratin loving"- Keratin is a major protein found in horns, hooves, nails, hair, and skin - use keratin as a source of nitrogen
• Do not penetrate the living tissues usually
• Fungal products cause local inflammation-hypersensitivity to fungal antigens is responsible for the vascular lesions or dermatophytids
  
  
  
• Hypersensitivity  detected by skin testing with the fungal antigen, trichophytin

Clinical Manifestations: – “ringworm” – Papules to pustules with clear center and active borders (peripheral pustules and scaling), itchy with inflammatory, vesicular, enlarging margins

Depending on the site involved

 • Tinea corporis (Tinea glabrosa) – ringworm of the smooth or non-hairy skin of the body

• Tinea imbricata (subtype of Tinea corpuris, concentric layers of lesions)

• Tinea cruris (groin and perineum area)

• Tinea fascie (face)

• Tinea barbae or barber’s itch- bearded areas of the face and neck

• Tinea pedis or athlete’s feet (ringworm of foot)

• Tinea capitis (ringworm of scalp)

• Tinea ungium (fingernails)

•Favus – chronic type of ringworm – dense crusts in the hair follicles, (honeycomb pattern of damage seen on surface of hair shaft), can lead to alopecia and scarring- scalp infection can result in lesions with marked inflammatory reaction called “kerion”

Laboratory Diagnosis

-KOH mounts of scrapings taken from edges of ringworm lesions

-Specimen mixed with a drop of 10% KOH on a slide, coverslip placed and the preparation gently heated to bring about “clearing”

-Microscopy reveals branched septate hyphae

-Wood’s lamp (UV light) is helpful in selection of infected hair for examination

-Two types of hair infection- “ectothrix”, in which arthrospores are seen as a sheath surrounding the hair and “endothrix”, in which spores are inside the hair shift

-Species identification by growing in Sabouraud’s medium (with antibiotics & cycloheximide) and incubated at room temperature- growth is slow and colonies appear only in 1-3 weeks

Epidemiology

Dermatophytosis occurs throughout the world

Certain manifestations show variations due to geographical, social and cultural differences eg., Tinea pedis- common in temperate climates (use shoes) but rare in the tropics (barefoot)

Age, hormones and intercurrent diseases affect the susceptibility to dermatophytoses

Depending on their natural habitat, dermatophytes maybe anthrophilic, zoophilic and geophilic species

Anthrophilic dermatophytes – human beings are the only or main hosts eg., T. rubrum, E. floccosum, M. audouinii – cause mild but chronic lesions

Zoophilic species – natural parasites of animals eg., T. verrucosum in cattle and M. canis in dogs and cats. Human infections with zoophilic dermatophytes cause severe inflammation but are more readily curable

Geophilic species, occur naturally in soil and rae relatively less pathogenic for humans eg., M. gypseum and T. ajelloi

Treatment

Topical antifungal agents are effective

T. rubrum infections may be resistant to treatment - Oral griseofulvin is the drug of choice