INTRODUCTION TO SUBCUTANEOUS MYCOSES –
Subcutaneous mycosis is principally found in tropical and subtropical regions. The fungi causing such subcutaneous mycoses are either normally present in the soil or are pathogens of plants. the various types of subcutaneous mycoses include –
- Mycotic Mycetoma
- Subcutaneous phycomycosis
⇒ Mycetoma is a chronic, granulomatous, post-traumatic infections of the subcutaneous tissue, usually affects the foot and rarely the other parts of the body
⇒ It is commonly known as Madura foot or Maduramycosis because it was first described by Gill from Madurai, South India, and is quite common in Tamil Nadu.
⇒ Causative agents and Types of Mycetoma
» Mycetoma have been classified into three groups as follows –
- Eumycetoma (Maduramycosis) – Mycetoma i.e. caused by Fungi.
- Actinomycetoma – Mycetoma i.e. caused by Filamentous bacteria.
- Botryomycosis – Mycetoma i.e. caused by Staphylococcus aureus & other bacteria.
CAUSATIVE AGENT COLOR OF GRANULES OR GRAIN TYPE OF MYCETOMA
Acremonium falciforme White – yellow Eumycetoma
Actinomadura madurae White – yellow Actinomycetoma
Actinomadura pelletierii Red Actinomycetoma
Madurella mycetoma Brown – black Eumycetoma
Madurella grisea Brown – black Eumycetoma
Streptomyces somaliensis Yellow Actinomycetoma
Exophiala jeanselmei Brown – black Eumycetoma
Scedosporium apiospermum White – Yellow Eumycetoma
Nocardia asteroides White – Yellow Actinomycetoma
Nocardia brasiliensis White – Yellow Actinomycetoma
Staphylococcus aureus Botryomycosis
⇒ Laboratory diagnosis of Mycetoma–
- Diagnosis is made from examination of granules or grains. Granules are microcolonies of the causative agents.
- The color and consistency of the granules vary with the different agents causing the disease.
- In Actinomycotic mycetoma, the granules are composed of very thin (<1mm in diameter) filaments
- In Mycotic lesions, granules are broader and often show septate and chlamydospores are present.
⇒ Sporotrichosis is a chronic infection involving Subcutaneous and Lymphatic tissue, characterized by formation of nodules and ulceration at the site of infection.
⇒ The infection is caused by thorn pricks or some injuries.
⇒ It is more common in gardeners and farmers.
⇒ The causative agent of Sporotrichosis is a thermally dimorphic fungus Sporothrix schenckii.
⇒ Laboratory diagnosis of Sporotrichosis–
- Specimens: the specimen collected in case of Sporotrichosis includes – aspirated fluid, Pus, Biopsy material, Skin scrapings and Swabs.
- Microscopy: direct microscopic examination of KOH mounts of necrotic material or histopathological examination of tissue sections stained by Methenamine silver stain may yield a diagnosis. The characteristic feature is the asteroid body: a rounded or oval, basophilic yeast-like body 3-5 mm in diameter, with rays of an eosinophilic substance radiating from yeast cell.
- Culture: the fungus may not be demonstrable in pus or tissue, hence culture is done on media incubated at 25°C and 37° Sporothrix schenckii is a dimorphic fungus occurring in yeast phase in tissues and in culture at 37°C and in mycelia phase in nature and culture at 25°C
- Identification: In yeast phase Sporothrix schenckii appears as cigar-shaped cells and mould form contains Hyphae carrying flower like clusters of small conidia.