Zygomycetes are a ubiquitously distributed group of fungi found commonly in soil, decaying organic matter, and on fruit and bread. The members of this group of fungi that infect humans include Mucor, Rhizopus, Absidia, and the Cunninghamella species. Given the wide distribution of these fungi, most humans are exposed to these organisms on a daily or weekly basis.[1,2,3]
Although first described by Paltauf in 1885, these infections were virtually unrecognized in the lungs until the advent of antimicrobial, immunosuppressive, and antineoplastic therapy. They rarely cause disease in immunocompetent hosts because of the low virulence of the organisms; however, they are now the third most common cause of invasive fungal infection in immunocompromised patients, especially stem-cell transplant recipients and patients with underlying hematologic malignancies.
These spore-forming saprophytes infect hosts via inhalation of aerosolized spores or from hematogenous spread. Colonization may be transient or persistent and depends upon host mucosal defense mechanisms and fungal virulence. After colonization, local disease may form and can progress to disseminated illness in susceptible hosts. Mucor are molds in the environment that become hyphal forms in the body tissues. Once the spores begin to grow, fungal hyphae invade blood vessels and produce tissue infarction, necrosis, and thrombosis. Neutrophils are the key host defense against these fungi; therefore, individuals with neutropenia or neutrophil dysfunction (diabetes, steroid use) are at highest risk. Few cases of mucormycosis have been reported in patients with AIDS, suggesting that the host defense against this infection is not primarily mediated by cellular immunity.[2,3,5]
The clinical manifestations of infection have traditionally been divided into six separate syndromes: rhinocerebral, pulmonary, cutaneous, gastrointestinal, central nervous system, and disseminated disease. Rhinocerebral and pulmonary involvement are the two most common syndromes. Rhinocerebral disease, the most common form, is most often seen in persons with diabetes, particularly those suffering from diabetic ketoacidosis. Between 50% and 75% of pulmonary mucormycosis infections occur in patients with hematologic malignancies.
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