Ecology and Epidemiology

Zygomycetes are common fungi in the environment and can be recovered from soil, decaying organic matter, or food stuffs. Most of the species have a worldwide distribution. Nevertheless, the two species Apophysomyces elegans and Saksenaea vasiformis have been mainly reported from tropical and subtropical areas and

Cokeromyces recurvatus seems to be restricted to the USA and some areas of Mexico (Ribes et al., 2000). Some zygomycetes have been recovered in extreme environments such as hot geothermal soil (Redman et al., 1999) or in the Antarctic (Lawley et al., 2004). The route of transmission is mainly airborne, but infection can also occur after ingestion or traumatic implantation. Outbreaks and pseudoepidemics of cutaneous or gastrointestinal zygomycosis have been reported in some instances.

Zygomycetes are mostly opportunistic pathogens responsible for infections in immunocompromised patients or patients with other predisposing factors. Integrity of the skin barrier as well as innate immunity mediated by mononuclear and poly-morphonuclear phagocytes prevent development of infection in an immunocompe-tent individual. Therefore, risk factors for zygomycosis comprise conditions in which these defense mechanisms are altered. The clinical presentation of the disease will vary depending upon the risk factors (Roden et al., 2005). Diabetes mellitus, and particularly in patients with ketoacidosis, is a well-known and common risk factor for zygomycosis. In these patients sinus and rhinocerebral infections are the most common. Iron is an important growth factor for zygomycetes and iron overload has been identified as a risk factor for zygomycosis. Paradoxically, deferoxamine therapy used for treatment of iron and aluminum overload in dialysis patients has also been recognized as an important risk factor for zygomycosis. In fact, it has been shown that deferoxamine, by chelating iron, acts as a siderophore, making iron more easily available to the fungus. A large number of these patients had disseminated zygomycosis. Immunosuppression either in patients with cancer or hematological malignancies or in solid-organ transplant recipients is a major risk factor. In these patients, neutropenia and corticosteroid therapy used for graft-versus-host disease, are the main factors that enhance the risk of infection. In patient with malignancy, bone marrow or solid organ transplantation, pulmonary zygomycosis is the most frequent form. Other underlying conditions predisposing to zygomycosis include traumas and burns, HIV infection, and intravenous drug abuse.

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