Dermatophytosis

DERMATOPHYTOSIS

Synonyms

  • Athlete's foot, Jock Itch, Ringworm (Tinea), Favus (crusted ringworm - Trichophyton schoenleinli), Microsporosis, Trichophytosis

Type of zoonosis

  • Direct anthropozoonosis or Zooanthroponosis, Saprozoonosis

Definition

  • Dermatophytosis is a superficial mycotic saprozoonotic diseases affecting skin, hair or nails and characterized by redness of the skin, small popular vesicles, fissures and scaling, and it is commonly known as "ringworm".

Etiology

  • Dermatophytosis is multi-etiologic in origin.
  • Species of Trichophyton, Microsporum and Epidermophyton are involved in human dermatophytosis.
  • Dermatophytes are classified into
    • Anthropophilic dermatophytes (infect humans)
    • Zoophilic dermatophytes (infect animals)
    • Geophilic dermatophytes (saprophytes)
  • Trichophyton verrucosum from cattle and horses to man.
  • Trichophyton mentagrophytes is transmitted from rodents to man.
  • Microsporum canis from dogs and cats to man.

Reservoir and incidence

  • Most species of dermatophytes have distributed worldwide. In India, T.simii is commonly distributed.
  • Fungal spores are viable for long period of time on fomites.
  • All domestic and companion animals, and rodents are the reservoir hosts, and exposure to the reservoirs results in incidence of dermatophytosis in humans.
  • Pet animals may also acquire disease from humans.

Transmission

  • Direct or indirect contact spreads dermatophytes to humans.
  • It is also spread by aerosols, especially from contaminated bedding materials and dust.

Disease in animals

  • Rodents and cats are often asymptomatic to dermatophytes.
  • In dogs, it develops characteristic skin lesions, include dermatitis with local loss of hair. Inflammatory and severe hypersensitivity reactions develop due to deeper invasion of dermatophytes.
  • In the hair cortex, hyphae grow and accumulate arthroconidia (on the surface of the hair). This pattern is called ectothrix, is characteristic of all classical animal dermatophytosis.

Disease in man

  • Symptoms of dermatophytosis in human are mild and self limiting.
  • In case of clinical dermatophytosis, the signs include scaling, redness and occasionally vesicles or fissures, thickening and discolouring of nails.
  • Skin lesions show circular pattern of development, which is clear in the centre forming a ring.
  • Dermatophytic skin lesions in man are categorized as:
    • Tinea capitis – infection on scalp and hair
    • Tinea corporis – infection on body (extremities, arm and hand)
    • Tinea pedis – infection on foot / Athlet's foot
    • Tinea unguium – infection on nails
    • Tinea barbae - infection of beard / Barber's itch
    • Tinea interdigitale - infection of inter digital space

Diagnosis

  • Skin scraping from active periphery region of the lesion, nail scrapings and hair follicles should be collected for microscopic examination.
  • Microscopic examination reveals the presence of branching hyphae and chains of arthroconidia in positive cases (sample should be treated with 10% KOH and heated gently before examination).
  • Wood's lamp technique can be followed, i.e. ultraviolet light gives bright greenish blue fluorescence.
  • Lactophenol cotton blue staining improves visualization of branching hyphae and chains of arthroconidia in positive cases.
  • Isolation and identification by culture of suspected skin scrapings in selective SDA media (Sabouraud’s Dextrose Agar with chloramphenicol).

Table: Diagnostic morphological features of different fungi

Characters

Microsporum

Trichophyton

Epidermophyton

Macroconidia

Usually present

Variable (often absent)

Present

Walls

Thick

Thin

Thick

Surface

Rough

Smooth

Smooth

Shape

Spindle

Club (slender)

Cigar, smooth (broad)

Microconidia

Variable

Usual

Absent

Treatment

  • Moist softening and fissuring stage
    • Athlete's foot: Aqueous aluminum chloride (30% solution) can be applied.
    • Aluminum subacetate solution with potassium permanganate can be applied.
    • Imidazole cream (broad spectrum antifungal drug) can be used.
  • Dry and scaly stage
    • Administration of antifungal drugs (primary used for Trichophyton infection).
      • Griseofulvin @ 25 mg/kg body weight for at least 30-60 days
      • Ketoconazole @ 1.5 to 2 /kg body weight for at lest 3 to 4 weeks
    • Application of topical antifungal creams
      • Nystatin or miconazole or clotrimazole or ketoconazole
      • Griseofulvin or ketoconazole is recommended for severe cutaneous infections
      • Betamethasone dipropionate with clotrimazole is recommended for acutely inflamed tinea lesions

Prevention and control

  • Newly purchased animals should be examined for any fungal infection.
  • Infected animals should be identified and treated with antifungal drugs.
  • Protective gloves and clothing should be used while handling infected animals.
  • Hands should be washed after handling of animals.
  • Routine sanitization of contaminated premises using chlorine, iodine or phenol-containing disinfectants should be followed.
  • Disinfection of utensils and equipment should be followed.
Last modified: Wednesday, 16 May 2012, 5:40 AM