(From Micro, 13 Oct 2000, by Brian Buschman)
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Fungi are eukaryotic cells that require an aerobic environment. Their cell membranes have sterols like ours primarily ergosterol (cholesterol is our main one). There is a carbohydrate cell wall around the cell membranes. Sometimes a capsule around that.
They are classified by mode of reproduction and mode of action. Reproductively some are diploid and need some sexual form. These are called teleomorphic while asexual ones are called anamorphic and appear in a haploid state.
Superficial fungal infections are completely superficial and do nothing other then affect the color of the skin or hair. Pityriasis versiculor (tinia versicolor) is a chronic problem with hyper- or hypo- pigmentation. It looks like uneven tanning. It is caused by Malassezia furfur.
Tinia nigra is caused by Exophiala werneckii and causes black patches on hands and feet.
You Dx either with KOH treatment of skin scrapings. The KOH dissolves al skin cells leaving the fungi. It’s treated with dandruff shampoo (selenium sulfide).
Two others include white piedra (trichsporon beigelii) has a light brown, nodule on hair. Black piedra is caused by Piedraia hortae and has black pellets on growing hair.
Cutaneous infections are often caused by Micosporum, Trichophyton and Epidermophyton. They include:
1) Tinea corporis (ringworm)
2) Tinea cruris (jock itch)
3) Tinea pedis (athlete’s foot)
4) Tinea capitis (scalp)
5) Tinea unguium (nails)
It involves the horny layer of the skin and dissolves keratin so you see scaling of the skin. Diagnosis is with KOH to again digest the skin cells leaving the fungi. Some microsporum will fluoresce a bright green.
Treatment is with topical miconazole or tolnaftate for all. You can also treat T. capitis (scalp) and T. unguium (nails) with oral griseofulrin.
Most fungal infections get in with tissue trauma and they stay in the local sub-q area or spread to regional nodes.
1) Sporotrichosis – sporathrix schenekii. Sporothrix is a fungus that hangs out around thorns. It causes sub-q nodules that can ulcerate. They spread up the arm a little.
Culture them at 25oC gets branching hyphae but culture at 37oC gives yeast. Treat with potassium iodide.
2) Chromoblastomycosis (Phialophora & Cladosporium).
Phialophora and Cladosperium come from puncture wounds near rotting wood. They are copper containing and KOH treatment of the scrapings reveals Cu bodies. They cause purple cauliflower like warts nearby. Treat with itraconazole.
3) Eumycotic mycetoma
Eumycotic mycetoma are fungi in soil and decaying plants that get in with trauma. They have abscesses and sinuses that ooze fluid. Diagnose by analyzing fluid after KOH treatment of skin scrapings. Treat with surgical extraction.
The systemic infections are usually inhaled spores released into the air. They are not transmitted person to person. They are dimorphic in that they grow as a mold with spores at 25oC on Sabourand’s agar and at 37oC on blood agar as a yeast. This is the explanation for not being transmitted person to person.
It is inhaled as a spore in SW US or Northern Mexico. Most patients are asymptomatic and get over coccidioides on their own. One third will get flue-like symptoms, some get pneumonia similar to TB (low grade fever and night sweats). Some, especially AIDS patients, get a chronic disseminated form.
You can check for exposure with a PPD test but you need to do a biopsy of affected tissue and stain with KOH or silver or culture on Sabourand’s agar at 25oC. You can also study the serology by checking for IgM or IgG precipitation.
Treat all systemic fungi with amphotericin B.
Histoplasma is common to the Mississippi river watershed. It, like Coccidioides, is usually asymptomatic. It may have some granulomastous legion that develops, heals and calcifies.
Diagnose with culture on Sabourand’s agar or serologically test with LPAT. Treat with amphotericin B.
It is also found in the Mississippi river basin all the way up to the great lakes. Most are asymptomatic but most that appear show pneumonia or disseminated cases. Disseminated cases have low grade fever with night sweats.
Diagnose with KOH mounts of sputum or culture on Sabourand’s agar to look for tan colonies. Treat with amphotericin B.
Cryptococcus is similar to the other three being inhaled as a spore but it primarily causes meningoencephalitis not pneumonia. It is usually associated with immunosuppression.
It is diagnosed by examination of CSP sediment with India ink for encapsulated yeast. It is treated with amphotericin B.
Candida is normal flora that can cause three cutaneous infections in normal people as well as two more states in the immunosupressed.
1) Oral thrush has creamy white exudate in the mouth.
2) Vaginitis (yeast infections) with vaginal itching, discharge and cottage-cheese appearance.
3) Dipper rash.
In the immunosupressed you see:
4) Espohagalitis is a painful extension of oral thrush into the esophagus.
5) Disseminated Candida invades the blood and all organs. Fluffy candidal patches are seen on retina. It is normal flora in the moth and vagina but NOT in blood or internal organs.
Diagnosis is with KOH preparations and treatment is with amphotericin B.
Aspiration of Aspergillus is a big problem in that it causes both IgE mediated reactions (Type I hypersensitivity) and a delayed hypersensitivity reaction in the lungs.
People with existing lung problems can grow an aspergilloma that needs surgical removal.
Aspergillus also makes aflatoxin that contaminates all sorts of foods around the world.
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