Subcutaneous mycoses

Are a group of fungal diseases produced by a heterogeneous group of fungi that infect the skin, subcutaneous tissue, and in some cases the underlying tissues and organs.

The causative agents are commonly found in the soil and organic material, and are introduced by traumatic injury of the skin.

A.Chromoblastomycosis Is a fungal infection of the skin and subcutaneous tissue. It can be caused by many different types of fungi which become implanted under the skin, often by thorns or splinters. Chromoblastomycosis spreads very slowly; it is rarely fatal but it can be very difficult to cure. The etiologic agents of chromoblastomycosis are generally members of three genera of fungi that inhabit the soil:

I. Fonsecaea sp.: Produces septate, dark brown hyphae, conidia are brown and barrel-shaped.

II.Phialophora sp.: The conidiophores are short, their conidia are unicellular and produced from a flask shaped phialide.

Fonsecaea sp Phialophora sp.

I. Cladosporium sp.: live-green to brown or black colonies, and have darkpigmented conidia that are formed in simple or branching chains.

Cladosporium sp

Laboratory Diagnosis: 1. Clinical Material: Skin scrapings and/or biopsy.

2. Direct Microscopy: a. Skin scrapings should be examined using 10% KOH and Parker ink or calcofluor white mounts

b. Tissue sections should be stained using H&E. Note: direct microscopy or histopathology does not offer a specific identification of the causative agent.

3. Culture: Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's dextrose agar.

Identification: Culture characteristics and microscopic conidial morphology are important, the arrangement of conidia, slide culture preparations are recommended.

5. Serology: There are currently no commercially available serological test for the diagnosis of chromoblastomycosis.

B. Phaeohyphomycosisis a chronic mycotic infection of humans and animals caused by a number of dematiaceous (brown-pigmented)Subcutaneous phaeohyphomycosis is characterised by papulonodules, verrucous, hyperkeratotic, cysts, abscesses, non-healing ulcers or sinuses.

The etiological agents include various dematiaceous hyphomycetes especially species of Exophiala, Phialophora, Aureobasidium, Cladosporium, Curvularia and Alternaria.

C. Sporotrichosis This fungal disease usually affects the skin, other rare forms can affect the lungs, joints, bones, and even the brain. Because the fungus is naturally found in soil, hay and plants, it usually affects farmers, gardeners, and agricultural workers. It enters through small cuts in the skin to cause the infection, it progresses slowly. The first symptoms may appear 1 to 12 weeks after the initial exposure to the fungus. Serious complications can also develop in immune compromised patients.

Sporothrix schenckii: Produces septate hyaline hyphae. Conidia have two types. The first type is unicellular, hyaline to brown, oval, thin-walled, and are typically arranged in rosette-like clusters at the tips of the conidiophores.

The second type of conidia are brown, oval or triangular, thick-walled, sessile attached directly to the sides of the hyphae.

Clinical manifestations: Fixed cutaneous sporotrichosis: Primary lesions develop at the site of implantation of the fungus, usually at more exposed sites mainly the limbs, hands and fingers. Lesions often start out as a painless nodule which soon become palpable and ulcerate often discharging purulent fluid. Importantly, isolates from these lesions grow well at 35oC, but not at 37oC.

Sporothrix schenckii

Laboratory diagnosis: 1. Clinical material: A tissue biopsy is the best specimen. 2. Direct Microscopy: Tissue sections should be stained using PAS digest or Gram stain. 3.Culture: Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's dextrose agar and Brain heart infusion agar supplemented with 5% sheep blood. 4.Serology: Serological tests are of limited value in the diagnosis of Sporotrichosis.