Zygomycosis

Updated: Aug 12, 2015
  • Author: Jose A Vazquez, MD, FACP, FIDSA; Chief Editor: Mark R Wallace, MD, FACP, FIDSA  more...
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Overview

Background

Mucormycosis is an infection caused by fungi in the orders Mucorales and Entomophthorales. Previously, the term zygomycosis was used to denote invasive fungal infections (IFIs) caused by the fungi belonging to the phylum Zygomycota, class Zygomycetes, orders Mucorales and Entomophthorales. The Mucorales order contains 2 families—Mucoraceae and Cunninghamellaceae. [1] Since the majority of human infections are caused by Mucorales fungi, the term Mucormycosis is now used to designate this infection. [2]

The terms mucormycosis and zygomycosis are used interchangeably here. The Entomophthorales constitute the second order and includes (Conidiobolus species and Basidiobolus species). [1, 3] During the past decade, mucormycosis has emerged as a common causes of IFI. [4, 3, 5, 6, 7]

The pathogens that cause mucormycosis are commonly found in the environment on fruit, on bread, and in soil and are common components of decaying organic debris. [1] These organisms are ubiquitous and generally saprophytic, rarely causing disease in immunocompetent hosts, but they are the third-most-common cause of invasive fungal infection in immunocompromised patients, especially stem cell transplant recipients and patients with underlying hematologic malignancies. [4, 8, 9, 10, 11]

Fungi are ubiquitous in the natural world, often found in association with plants, mammals, and insects. Accordingly, humans are continually exposed to multiple genera of fungi via various routes, including the respiratory and gastrointestinal routes, which allow the possibility of colonization. Depending on the interaction between host mucosal defense mechanisms and fungal virulence factors, colonization may be transient or persistent, or local disease may ensue.

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Pathophysiology

Overall, Rhizopus species from the Mucoraceae family are the most commonly identified etiologic agents of zygomycosis in humans. Of the Rhizopus species, the most common agent associated with zygomycosis is Rhizopus arrhizus (Rhizopus oryzae), followed by Rhizopus rhizopodiformis. Other causes include Mucor species, Cunninghamella bertholletiae, Apophysomyces elegans, Lichtheimia (Absidia species), Saksenaea species, Rhizomucor pusillus, Entomophthora species, Conidiobolus species, and Basidiobolus species. [4, 11, 12, 7]

Infections caused by R arrhizus are frequently acute and rapidly fatal despite early diagnosis and treatment. These organisms have a particular predilection for invading major blood vessels, with ensuing ischemia, necrosis, and infarction of adjacent tissues, resulting in the production of black pus. Persons at particular risk include patients with granulocytopenia, hematopoietic stem cell transplant and solid organ transplant recipients, and patients with underlying acidosis. [13] For unknown reasons, agents of mucormycosis have a propensity to affect patients with acidosis, particularly those with diabetes. In addition, they also infect patients with acidosis secondary to renal insufficiency, diarrhea, and aspirin intake. Patients who are receiving glucocorticoids or deferoxamine and those who have undergone splenectomy also are at risk. [10, 11, 12, 14]

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Epidemiology

Frequency

International

The distribution of the various forms of zygomycosis is uniform regardless of age, geography, or race.

Mortality/Morbidity

The overall mortality rate associated with zygomycosis is approximately 50% and has remained at this level for the past 50 years. Rhinocerebral zygomycosis carries a mortality rate of approximately 85%. Mortality rates are very high because, by the time zygomycosis is suspected and diagnosed, it has frequently spread diffusely and caused extensive tissue destruction. However, the risk of mortality varies depending on the characteristics of the host, the type of infection, the site of infection, and the use of surgical intervention. In general, antifungal therapy and surgical management independently decrease the likelihood of death. [11]

Sex

According to the latest epidemiologic surveys, approximately two thirds of all zygomycosis cases occur in males. The reason for this discrepancy is poorly understood.

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