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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Candida, Aspergillus, and Other Opportunistic Fungi

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Zygomycetes and Zygomycosis

Zygomycosis (mucormycosis) is the term applied to infection with any of a group of zy- gomycetes, the most common of which are Absidia, Rhizopus, and Mucor.

ZYGOMYCETES AND ZYGOMYCOSIS

Zygomycosis (mucormycosis) is the term applied to infection with any of a group of zy- gomycetes, the most common of which are Absidia, Rhizopus, and Mucor. These fungi are ubiquitous saprophytes in soil and are commonly found on bread and many other foodstuffs. They occasionally cause disease in persons with diabetes mellitus and in im-munosuppressed patients receiving corticosteroid therapy. Diabetic acidosis has a particu-larly strong association with zygomycosis.

Pulmonary or rhinocerebral disease is acquired by inhalation of conidia. The pul-monary form has clinical findings similar to those of other fungal pneumonias; the rhinocerebral form, however, produces a dramatic clinical syndrome in which agents of zygomycosis show striking invasive capacity. They penetrate the mucosa of the nose, paranasal sinuses, or palate, often resulting in ulcerative lesions. Once beyond the mu-cosa, they progress through tissue, nerves, blood vessels, fascial planes, and often the vi-tal structures at the base of the brain. The clinical syndrome begins with headache and may progress through orbital cellulitis and hemorrhage to cranial nerve palsy, vascular thrombosis, coma, and death in less than 2 weeks.

The pathologic cerebral and pulmonary findings are distinctive: the zygomycetes in-volved all show ribbon-like nonseptate hyphae in tissue which are so large their branch points can be difficult to visualize. Conidia are not seen. As with Aspergillus, tissue biop-sies are necessary to demonstrate the invasive hyphae, unless they can be seen on scrap-ings from palatal or nasal ulcers. For reasons that are obscure, cultures are sometimes negative, even those from tissue containing characteristic hyphae. Therapy involves con-trol of underlying disease, amphotericin B, and occasionally surgery.


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