mycology essay

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Medical Mycology Module (3130) Essay: Coccidioides immitis Introduction Coccidioides spp is a dimorphic fungus endemic in parts of the Western hemisphere causing a range of disease from asymptomatic infection to fatal disseminated disease. This review focuses upon its taxonomy, species identification, pathophysiology, investigation, treatment and prevention. Taxonomy Coccidioides is classified into two species, C. immitis and C. posadasii, which are distinct genetically and in geographic range but are otherwise identical. (1). It is closely related to the non-pathogenic soil fungus Uncinocarpus reesii. (2) Currently Coccidioides is classified in the division Ascomycota, class Dikaryomycota, order Onygenales and family Onygenaceae. (3) Ecology C. immitis is found preferentially in alkaline sandy clay soils in warm dry climates with a high salt content between 10-30cm below the surface.(4, 5) It’s distribution through the soil is patchy, concentrated around animal burrows or soils rich in nitrogen containing animal excreta, persisting for extended periods in the environment.(5) Species identification C. immitis is non-fastidious growing on a variety of culture media including brain-heart infusion agar, potato-dextrose agar, Sabourand-dextrose agar and blood agar. (3) Culture to induce mycelial growth is best at 28-30oC typically taking 2-3 weeks with growth detectable within 5 days. (3, 6, 7) The colony is initially white and glabrous, quickly becoming floccose resembling angel hair (see picture 1) and turning brown as it ages. (3, 6) Microscopically the culture shows single celled barrel-shaped alternate arthroconidia (see picture 2) separated from each other by a disjunctor cell.(6, 8) Conversion to the yeast / spherule form re... ... middle of paper ... ...unity against Coccidioides. (3) This is no longer performed in the USA. (3) Coccidioides infection can be demonstrated by an antigen based ELISA using Coccidioides galactomannan. When performed upon urine a sensitivity of 71% and specificity of 99% was demonstrated. (26)The test performed best in patients with severe forms of the disease. Cross reactions with other endemic mycoses occurred in 10% of patients. (26) Real time polymerase chain reaction (PCR) targeting the Coccidioides internal transcribed spacer 2 (ITS2) and Antigen 2/proline rich antigen gene (Ag2/PRA) have been developed. When applied to respiratory tract and cerebrospinal fluid samples, they offer a sensitivity of up to 100% and a specificity of up to 98% and a short time to diagnosis. (30) Current PCR assays are predominantly in house or reference laboratory tests and not commercialised. Treatment

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