Thursday, January 24, 2008

Possible Fungal Agents

1. Dermatophytes (Epidermophyton, Microsporum, and Trichophyton species)
Transmission: Direct contact with the skin scale
Pathogenesis: Fungi only grow in the superficial keratinized layer of the skin. Presences of lesions are due to the inflammatory response to the fungi. Frequency of infection is enhanced by moisture and warm.
Clinical Symptoms: May present as asymptomatic, usually mild itching lesion with a scaling, inflammation usually manifest as a vesicular or bullous disease.
Laboratory Diagnosis: Skin scale is examined microscopically in a KOH preparation for the presence of hyphae. It is identified by the appearance of its mycelium and it asexual spore on SDA plates.
Treatment: Topical anti-fungal agents such as miconazole, clotrimazole or tolnaftate are used
Prevention: Practise personal hygiene such as chamging sock frequently, wiping area between toes to keep it dry.

2. Histoplasma capsulatum
Transmission: Inhalation of airborne sexual spores. Mould grows preferentially in soil enriched with bird dropping. It also grows well in a warm and moist environment, prevalent in Americas, India and southeastern Asia.
Pathogenesis: Microcondia (spores) enter the lungs and differentiate into yeast cells. The yeast cells are ingested by the alveolar macrophages and multiply within them.
Clinical Symptoms: Non-specific respiratory symptoms such as cough and flu. Enlargement in spleen, adrenal can be seen in severe infection.
Laboratory Diagnosis: Sputum can be examined microscopically and cultured on SDA plate. Presence of tuberculate chylamydospores in culture at 25 degree Celsius is diagnostic.
Treatment: Amphotericin B for disseminated disease; itraconazole for pulmonary disease
Prevention: No vaccine is available

3. Coccidioides Immitis
Transmission: Inhalation of airborne arthrospores. It grows well in the soil of arid regions.
Pathogenesis: Arthrospores differentiate into spherules in the lungs. Spherules rupture, releasing endospores that form new spherules, spreading the infection within the body.
Clinical Symptoms: Fever, mild respiratory distress, rashes
Laboratory Diagnosis: Sputum should be examined microscopically for spherules and cultured on SDA plate.
Treatment: Amphotericin B or itraconazole for disseminated disease
Prevention: No vaccine is available

4. Crytococcus neoformans
Transmission: Inhalation of airborne yeast cells. This heavily encapsulated yeast grows well in soil enriched by bird dropping (especially pigeon droppings).
Pathogenesis: Yeast cells spread via the bloodstream to the meninges. Reduced cell-mediated immunity pre-disposes to severe disease, cryptococcal meningitis occur in immunocompetent people.
Clinical Symptoms: May present as asymptomatic, usually pneumonia-like symptoms such as flu and fever, unusual sweating at night, skin rash, chest pain, confusion, nausea
Laboratory Diagnosis: Gram stain is not preferred due to reliable result. Stain such as methenamine-silver, periodic acid-Schiff will allow the organism to be visualized. Colonies are presented as mucoid due to presence of large amount of capsular polysaccharide. Serologic test such as cryptococcal antigen test can be used to determined organism presence.
Treatment: Combined treatment with amphotericin B and flucytosine is used in disseminated disease and meningitis.
Prevention: No known specific mean of prevention.

5. Aspergillus fumigatus
Transmission: Inhalation of airborne spore (conidia)
Pathogenesis: It exists as an opportunistic pathogen, invasive in immunocompetent patient. The organism invades the blood vessels, causing thrombosis and infarction. “Fungal ball” may be developed in tuberculosis patient and allergic brochopulomonary asperigillosis may developed in allergic patient.
Clinical Symptoms: Fever, weakness, chest pain, aches, blood in urine.
Laboratory Diagnosis: Examined microscopically for invasive septate hyphae. Form characteristic mycelium when cultured on SDA plate.
Treatment: Amphotericin B for invasive asperigillosis. Lesion such as fungal ball can be surgically removed. Steroid therapy is recommended for allergic brochopulomonary asperigillosis
Prevention: No vaccine or prophylactic drug is available

1) WARREN LEVINSON, MD, PhD (2006) REVIEW OF Medical Microbiology and Immunology. NINTH EDITION; McGraw-Hill company
2)> search> organism name
3) MMIC lectures notes

Yeo Ching Wei

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