Mycology - True Pathogens (Superficial, Cutaneous, Subcutaneous Infections) Flashcards
What are the four types of infection caused by true pathogens? What do these affect?
- Superficial cutaneous (dead skin, scales)
- Cutaneous (skin, hair, nail)
- Subcutaneous (lymphatic system, dermis)
- Systemic (internal organs)
What are the two main superficial cutaneous mycoses? What are their causative fungi?
- Tinea versicolour (Malassezia furfur)
- Tinea nigra (Hortaea werneckii)
Outline the epidemiology of Tinea versicolour.
- Common superficial fungal infection worldwide
- Most prevalent in tropical and subtropical regions (may affect up to 60% of tropics population)
- Animals are not affected
- Common in summer season
- Not found as a saprophyte in nature
- Transmission by direct or indirect transfer of infected keratinous material from one person to another (e.g. towel sharing)
What are the symptoms that present in Tinea vresicolour?
- Lesions are hypopigmented or hyperpigmened macules, involving mostly the upper trunk, arms, chest, shoulders, face and neck.
- Lesions are irregular, well distinguished patches of discolouration, sometimes raised and covered by scale.
- Lesions are asymptomatic, but may involve hair follicles leading to folliculitis, perifolliculitis, and rarely dermal abscess.
What superficial disease does Malassezia furfur cause? How can this be diagnosed?
Malassezia furfur can lead to Tinea versicolour, a superficial infection characterised by hypo-/hyperpigmented lesions. Malassezia infection can be diagnosed by:
-
Direct microscopic examination: 10% KOH preparation, then stain:
- Calcofluor white (fluorescent stain that binds chitin)
- PAS (stains organisms magenta, binds carbohydrates in cell wall)
- Culture: usually not necessary. On mycological media supplemented with olive oil (lipophilic yeast). Yeast-like colonies found in 5-7 days at 30ºC
- Diagnosis made from skin scrapings. Microscopy should show clusters of yeast cells and short, infrequent branched pseudo-hyphae.
How is Tinea versicolour treated?
- Spotaneous cure has been reported
- Generally chronic and persistent
- Topical azoles or selenium sulphide shampoo
- For widespread infection, oral ketoconazole or itraconazole can be used
What is the infectious agent of Tinea nigra?
Hortaea werneckii: black yeast (produce melanin in their walls)
Outline the epidemiology of Tinea nigra.
- Prevalent in tropical and subtropical areas
- Likely contracted by traumatic inoculation of the fungus into epidermal superficial layers
What are the symptoms that present in Tinea nigra?
- Tinea nigra appears as an irreular soliltary, pigmented macule, usually on the palms or soles without scaling or invasion
- Non-contagious
- Lesion grossly resembles malignant melanoma
How is Tinea nigra diagnosed?
- Microscopy: skin scraping mounted in 10% KOH, showing pigmented brown to dark septate hyphal elements and 2-celled yeast-like cells, with dark pigmented septa
- Culture: 25ºC, produces black colonies containing yeast-like (2-celled) annelloconidia (conidia with rings) in 1 week, later in 2-3 weeks mycelial forms are found
Cutaneous mycoses are caused by what three major species of fungi? What do they affect?
- Trichopython (skin, hair, nail)
- Microsporum (skin, hair)
- Epidermopython (skin, nail)
Outline cutaneous mycoses.
- Involves keratin-containing structures and moist areas
- Doesn’t invade sub-cutaneous tissues
- Mycelial and conidial forms are observed
- Cosmetic problem, but not life-threatening
- Virulence of fungi is low
- Worldwide distribution
- Trichopython, Microsporum, and Epidermopython are collectively called dermatophytes (derm- skin; phytos- plant), also called Tinea/ringworm
Outline Tinea capitis.
Tinea capitis is a disease of the scalp, eyebrows, and eye lashes. Can be caused by Microsporum canis, and Trychopython violaceum.
Outline Tinea corporis.
Tinea corporis is characterised by circular, raised lesions usually on the main trunk. Lesions heal towards the center, while being active on the borders crearing ‘rings’. Can be caused by Trichopython rubrum and Microsporum canis.
Outline Tinea facialis.
Tine facialis is characterised by raised, circular, scaly lesions on the face and neck. Can be caused by Trichopython gypseum, T. rubrum, and T. mentagrophytes.
Outline Tinea ungium.
Tinea ungium is a fungal infection of the nails, characterised by a black lesion under the nail. Causd by Trichopython rubrum, can be treatd with oral griseofulvin.
Outline how a cutaneous mycosis would be diagnosed.
- Clinical signs and symptoms, microscopic examination of tissue
- Samples: skin scales, hair and nail clippings
-
Microscopic examination: prepare sample with 10% KOH, examine for conidia and hyphae after 10-15 minutes.
- Microsporum: macroconidia
- Trichopython: microconidia
- Epidermopython: smooth wall microconidia, clusters of 2-3
- Microscopic examination of hair distinguishes endothrix from ectothrix infections: hairs with holes in shaft are endothrix, and hair with hyphae surrounding shaft are ectothrix
- Culture: SAB agar, identification microscopically by morphology of conidia and hyhae
How are cutaneous mycoses treated?
Topical creams containing azoles (miconazole, clotrimazol, econazole, itraconazole). Refractory infections require oral Griseofulvin or itraconazole, fluconazole. Infection of the nail usually requires oral therapy with Terbinafine or Griseofulvin.
Outline lymphocutaneous sporotrichosis.
A subcutaneous infection affecting the lymph nodes caused by Sporothrix schenckii, a dimorphic fungus ubiquitous in soild and decaying vegetation. The mycelia of S. schenckii is in the arrangement of a daisy.
Describe the epidemiology and pathogenesis of lymphocutaneous sporotrichosis.
- Epidemiology: sporadic and most common in warmer climates; Japan, North and South America
- Pathogenesis: enters the body after a local trauma, often seen in gardeners and may develop from a prick to the finger (rose-growers’ disease). Pricking a finger, a pustule develops and ulcerates, then leading to invasion of the lymphatic and ascends the arm, resulting in a chain of subcutaneous nodules that later ulcerate and discharge pus
How is lymphocutaneous sporotrichosis diagnosed and treated?
- Diagnosis: direct microscopy is usually negative, a biopsy is needed where asteroid bodies (yeast surrounded by amorphous material) can be seen. A confirmed diagnosis is made upon culture.
- Treatment: KI (potassoim iodide) over 3-4 weeks, side effects including nausea and salivary gland enlargement. Itraconazole is also the drug of choice.
Outline chromoblastomycosis (chromomycosis).
Chromomycosis is a subcutaneous fungal infection caused by inoculation of pigmented (dematiaceous) fungi that affect skin and subcutaneous tissues, characterised by development of slow-growing verrucous nodules or plaques.
Common in tropics due to lack of protective foorwear involving legs and arms in men. Non-contageous.
Describe the clinical manifestations of chromomycosis.
Subcutaeous fungal infection characterised by chronic, pruritic, progressive lesion and is resistant to treatment. Early lesions are small warty papules that enlarge slowly. Established infections appear as multiple large warty cauliflower-like growths that are usually clustered together within the same region involving ulceration and cyst formation.
Causes gross limb distortion. Secondary bacterial infections may lead to elephantitis.
Inflammatory reaction is granulomatous.
How is chromomycosis diagnosed?
- Microscopic examination: brown, pigmented, spherical fungal elements (“copper penny” bodies) with transverse and horizontal septae. Can be viewed with KOH.
- Culture: Olive black colonies, conidial structures may need weeks to months to incubate
How is chromomycosis treated?
Treatment usually ineffective due to advaced stage of infection upon presentation. Itraconazole and terbinafine are most effective. Can be combined with flucytosie in refractory cases. Surgical amputation in advanced cases.
Outline mycetoma.
Mycetoma is a subcutaneous fungal infection that appears as a localised abscess that discharges pus, serum, and blood through sinuses (abnormal channels). The defining characteristic is the presence of coloured granules composed of compact hyphae.
Can reseble chromomycosis, but lacks large wart-like lesions.
Outline the pathogenesis and clinical maifestations of mycetoma.
- Pathogenesis: begins in a wound or abrasion contaminated with soil. It may start in the form of a painless nodule.
- Manifestation: characterised by chronic granulomatous inflammation, and the formation of draining sinus tracts is common. The abscess from the sinus contains large aggregates of fungal hyphae (granules). Feet and legs are the most common sites of infection. Eventually muscle or bone involvement may ensue, and secondary bacterial infections may occur.
Outline the epidemiology for mycetoma.
Tropics with low rainfall; Africa and Indian subcontinent, but also seen in Brazil, Venezuela, and the Middle East; mostly men affected.
Outline the diagnosis and treatment of mycetoma.
- Diagnosis: depends of identifying coloured grains (black and white grains) in the pus and discharge. Occasionally a skin biopsy is necessary. Microscopy using KOH confirms diagnosis. Fungal grains contain short hyphae. Agar plates ciltured at 25 and 37ºC for up to six weeks.
- Treatment: usually unsucessful. Some response from AmB, itraconazole, ketoconazole, terbinafine. Amputation in severe cases.
