**5. Aspergilosis**

*Aspergillus* species are ubiquitous molds found in organic matter. Although more than 100 species have been identified, the majority of human illness is caused by *Aspergillus fumigatus* and *Aspergillus niger* and, less frequently, by *Aspergillus flavus* and *Aspergillus clavatus*. The transmission of fungal spores to the human host is via inhalation [72].

*Aspergillus* may cause a broad spectrum of disease in the human host, ranging from hypersensitivity reactions to direct angioinvasion. *Aspergillus* primarily affects the lungs, causing 4 main syndromes, including allergic bronchopulmonary aspergillosis (ABPA), chronic necrotizing *Aspergillus* pneumonia (or chronic necrotizing pulmonary aspergillosis [CNPA]), aspergilloma, and invasive aspergillosis. However, in patients who are severely immunocompromised, *Aspergillus* may hematogenously disseminate beyond the lung, potentially causing endophthalmitis, endocarditis, and abscesses in the myocardium, kidney, liver, spleen, soft tissue, and bone. *Aspergillus* is second to *Candida* species as a cause of fungal endocarditis. *Aspergillus* -related endocarditis and wound infections occur in the context of cardiac surgery [73].

ABPA is a hypersensitivity reaction to *A fumigatus* colonization of the tracheobronchial tree and occurs in conjunction with asthma and cystic fibrosis (CF). Allergic fungal sinusitis may also occur alone or with ABPA. Bronchocentric granulomatosis and malt worker's lung are 2 hypersensitivity lung diseases that are caused by *Aspergillus* species, but they are rare [74].

An aspergilloma is a fungus ball (mycetoma) that develops in a preexisting cavity in the lung parenchyma. Underlying causes of the cavitary disease may include treated tuberculosis or other necrotizing infection, sarcoidosis, CF, and emphysematous bullae. The ball of fungus may move within the cavity but does not invade the cavity wall; however, it may cause hemoptysis [75].

CNPA is a subacute process usually found in patients with some degree of immunosuppression, most commonly that associated with underlying lung disease, alcoholism, or long-term corticosteroid therapy. Because it is uncommon, CNPA often remains unrecognized for weeks or months and can cause a progressive cavitary pulmonary infiltrate [74].

164 Immunodeficiency

or hematologic malignancy [70].

context of cardiac surgery [73].

may cause hemoptysis [75].

accuracy of the test [71].

**5. Aspergilosis** 

sensitivity (78-100%); its specificity is much lower because other disease processes can result in an elevated LDH level. LDH levels appear to reflect the degree of lung injury. They should decline with successful treatment. Consistently elevated LDH levels during

Quantitative PCR for pneumocystis may become useful in distinguishing between colonization

In one study, patients with positive quantitative PCR but negative immunofluorescence for pneumocystis had a higher 1-year mortality but only in the context of systemic inflammatory conditions. There was no significant difference for patients with solid-organ

β-D-Glucan (BDG) is a cell-wall component of many fungi, including candida, aspergillus, and pneumocystis (but not the zygomycetes). It has been shown to be a sensitive test to detect PCP in a meta-analysis of 12 studies assessing the sensitivity, specificity and overall

*Aspergillus* species are ubiquitous molds found in organic matter. Although more than 100 species have been identified, the majority of human illness is caused by *Aspergillus fumigatus* and *Aspergillus niger* and, less frequently, by *Aspergillus flavus* and *Aspergillus clavatus*. The

*Aspergillus* may cause a broad spectrum of disease in the human host, ranging from hypersensitivity reactions to direct angioinvasion. *Aspergillus* primarily affects the lungs, causing 4 main syndromes, including allergic bronchopulmonary aspergillosis (ABPA), chronic necrotizing *Aspergillus* pneumonia (or chronic necrotizing pulmonary aspergillosis [CNPA]), aspergilloma, and invasive aspergillosis. However, in patients who are severely immunocompromised, *Aspergillus* may hematogenously disseminate beyond the lung, potentially causing endophthalmitis, endocarditis, and abscesses in the myocardium, kidney, liver, spleen, soft tissue, and bone. *Aspergillus* is second to *Candida* species as a cause of fungal endocarditis. *Aspergillus* -related endocarditis and wound infections occur in the

ABPA is a hypersensitivity reaction to *A fumigatus* colonization of the tracheobronchial tree and occurs in conjunction with asthma and cystic fibrosis (CF). Allergic fungal sinusitis may also occur alone or with ABPA. Bronchocentric granulomatosis and malt worker's lung are 2 hypersensitivity lung diseases that are caused by *Aspergillus* species, but they are rare [74].

An aspergilloma is a fungus ball (mycetoma) that develops in a preexisting cavity in the lung parenchyma. Underlying causes of the cavitary disease may include treated tuberculosis or other necrotizing infection, sarcoidosis, CF, and emphysematous bullae. The ball of fungus may move within the cavity but does not invade the cavity wall; however, it

and active infection, but these assays are not yet available for routine clinical use [69].

treatment may indicate therapy failure and a worse prognosis [68].

transmission of fungal spores to the human host is via inhalation [72].

Invasive aspergillosis is a rapidly progressive, often fatal infection, associated with significant mortality, with a rate of 30-95%, that occurs in patients who are severely immunosuppressed, including those who are profoundly neutropenic, those who have received bone marrow or solid organ transplants, and patients with advanced AIDS or chronic granulomatous disease. This infectious process is characterized by invasion of blood vessels, resulting in multifocal infiltrates, which are often wedge-shaped, pleural-based, and cavitary. Dissemination to other organs, particularly the central nervous system, may occur [76].

*Aspergillus* causes a spectrum of disease, from colonization to hypersensitivity reactions to chronic necrotizing infections to rapidly progressive angioinvasion, often resulting in death. Rarely found in individuals who are immunocompetent, invasive *Aspergillus* infection almost always occurs in patients who are immunosuppressed by virtue of underlying lung disease, immunosuppressive drug therapy, or immunodeficiency [73].

*Aspergillus* hyphae are histologically distinct from other fungi in that the hyphae have frequent septae, which branch at 45° angles. The hyphae are best visualized in tissue with silver stains. Although many species of *Aspergillus* have been isolated in nature, *A fumigatus* is the most common cause of infection in humans. *A flavus* and *A niger* are less common. Likely, this relates to the ability of *A fumigatus,* but not most other *Aspergillus* species, to grow at normal human body temperature. Human host defense against the inhaled spores begins with the mucous layer and the ciliary action in the respiratory tract. Macrophages and neutrophils encompass, engulf, and eradicate the fungus. However, many species of *Aspergillus* produce toxic metabolites that inhibit macrophage and neutrophil phagocytosis. Corticosteroids also impair macrophage and neutrophil function. Underlying immunosuppression (eg, HIV disease, chronic granulomatous disease, pharmacologic immunosuppression) also contributes directly to neutrophil dysfunction or decreased numbers of neutrophils. In individuals who are immunosuppressed, vascular invasion is much more common and may lead to infarction, hemorrhage, and necrosis of lung tissue. Persons with CNPA typically have granuloma formation and alveolar consolidation. Hyphae may be observed within the granulomata [77].

Because *Aspergillus* infection may cause colonization, allergy, or invasive infection, its manifestations are quite variable and are best considered based on the disease process. Allergic bronchopulmonary aspergillosis is defined by several abnormalities, including asthma, eosinophilia, a positive skin test result for *A fumigatus,* marked elevation of the serum immunoglobulin E (IgE) level to greater than 1000 IU/dL, fleeting pulmonary infiltrates, central bronchiectasis, mucoid impaction, and positive test results for *Aspergillus* precipitins (primarily immunoglobulin G [IgG], but also immunoglobulin A and immunoglobulin M, antibodies). Minor criteria for diagnosis include positive *Aspergillus* radioallergosorbent assay test results and culture findings for *Aspergillus* in sputum [74].

Fungal Infections in Immunosuppressed Patients 167

are present and BAL testing is performed in the suspicious area. A meta-analysis and systematic review determined that the measurement of BAL-galactomannan levels may help

A study by Luong et al of 150 BAL samples from lung transplant recipients concluded that real-time polymerase chain reaction (PCR) assays could be useful in diagnosis of invasive aspergillosis in high-risk populations. Pan-*Aspergillus* PCR combined with BAL galactomannan testing was 97% specific and 93% sensitive for invasive pulmonary aspergillosis. Species-specific real-time PCR assays for *A fumigatus* and for *A terreus* could be used to rule out or identify the common *A fumigatus* and the amphotericin B-resistant *A* 

Histopathology and silver staining for persons with invasive aspergillosis demonstrates the characteristic septate hyphae, branching at acute angles, and acute inflammatory infiltrate and tissue necrosis with occasional granulomata and blood vessel invasion. The airways of patients with ABPA contain mucus filled with degenerating eosinophils and typical fungal hyphae. ABPA may occur on a background of chronic eosinophilic pneumonia and bronchiolitis, granulomatous bronchitis, bronchocentric granulomatosis, and, occasionally,

Selection of therapy also needs to consider the certainty of the diagnosis. Voriconazole, itraconazole, the investigational azoles with anti-mould activity, and amphotericin B all possess a reasonably broad-spectrum of activity against *Aspergillus* and the related hyaline moulds. Their activity does, however, vary for the agents of zygomycosis, with posaconazole being the azole with the most reliable activity against this class of fungi. The echinocandin glucan synthesis inhibitors (caspofungin, FK463, and anidulafungin) possess a narrower spectrum of activity and should only be used if the infection is known to be due to

Zygomycosis is an infection caused by fungi in the orders Mucorales and Entomophthorales. The Mucorales order contains 2 families exist—Mucoraceae and Cunninghamellaceae. Mucormycosis is another common name applied to this same group of diseases. This designation reflected the predominance of the Mucorales in causing disease in humans. However, this term ignored the role of the Entomophthorales (*Conidiobolus* species and *Basidiobolus* species). The currently accepted designation is zygomycosis, reflecting all disease processes caused by the members of the class Zygomycetes. During the past decade, the Zygomycetes have emerged as common causes of invasive fungal

The pathogens that cause zygomycosis are commonly found in the environment on fruit, on bread, and in soil and are common components of decaying organic debris. 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

in diagnosing invasive aspergillosis early [81, 82].

*terreus* [83].

BOOP [84].

*Aspergillus* spp [85, 86].

**6. Zygomycosis** 

infections [87].

**Figure 3.** Grocott's methenamine silver (GMS) stained tissue section of lung showing fungal balls of hyphae of *Aspergillus fumigatus.* (Courtesy: www.mycology.adelaide.edu.au)

Diagnostic criteria for ABPA in persons with CF were revised by the Cystic Fibrosis Foundation. ABPA is considered a definite diagnosis requiring treatment if the following are noted: (1) clinical deterioration, including cough, wheeze, increased sputum production, diminished exercise tolerance, or diminished pulmonary function; (2) total serum IgE level greater than 1000 IU/mL or a greater than 2-fold rise from baseline; (3) positive serology results for *Aspergillus* (*Aspergillus* precipitins or *Aspergillus* -specific IgG or IgE); and (4) new infiltrates on chest radiographs or CT scans. Treatment for ABPA is also recommended in patients with CF who have new radiographic findings and symptoms and a change in baseline IgE level to greater than 500 IU/mL [79].

Definitive diagnosis of invasive aspergillosis or chronic necrotizing *Aspergillus* pneumonia depends on the demonstration of the organism in tissue [76].

In the appropriate clinical setting of pulmonary infiltrates in a patient who is neutropenic or immunosuppressed, visualization of the characteristic fungi using Gomori methenamine silver stain or Calcofluor or a positive culture result from sputum, needle biopsy, or bronchoalveolar lavage (BAL) fluid should result in the prompt institution of therapy. This is especially important after bone marrow transplantation because a positive *Aspergillus* culture result from sputum has a 95% positive predictive value for invasive disease. However, a negative fungus result from culture of sputum or BAL fluid does not exclude pulmonary aspergillosis because *Aspergillus* is cultured from sputum in 8-34% of patients and from BAL fluid in 45-62% of patients eventually found by biopsy or autopsy to have invasive disease [80].

An assay to detect galactomannan, a major component of the *Aspergillus* cell wall, is available. Patients who are at high risk, such as those who have received stem cell transplants or who have prolonged neutropenia, may be screened for the development of invasive *Aspergillus* infection by monitoring serum galactomannan levels weekly.The presence of an elevated galactomannan level in BAL fluid may also be helpful in the diagnosis of pulmonary aspergillosis in patients in whom compatible radiographic changes are present and BAL testing is performed in the suspicious area. A meta-analysis and systematic review determined that the measurement of BAL-galactomannan levels may help in diagnosing invasive aspergillosis early [81, 82].

A study by Luong et al of 150 BAL samples from lung transplant recipients concluded that real-time polymerase chain reaction (PCR) assays could be useful in diagnosis of invasive aspergillosis in high-risk populations. Pan-*Aspergillus* PCR combined with BAL galactomannan testing was 97% specific and 93% sensitive for invasive pulmonary aspergillosis. Species-specific real-time PCR assays for *A fumigatus* and for *A terreus* could be used to rule out or identify the common *A fumigatus* and the amphotericin B-resistant *A terreus* [83].

Histopathology and silver staining for persons with invasive aspergillosis demonstrates the characteristic septate hyphae, branching at acute angles, and acute inflammatory infiltrate and tissue necrosis with occasional granulomata and blood vessel invasion. The airways of patients with ABPA contain mucus filled with degenerating eosinophils and typical fungal hyphae. ABPA may occur on a background of chronic eosinophilic pneumonia and bronchiolitis, granulomatous bronchitis, bronchocentric granulomatosis, and, occasionally, BOOP [84].

Selection of therapy also needs to consider the certainty of the diagnosis. Voriconazole, itraconazole, the investigational azoles with anti-mould activity, and amphotericin B all possess a reasonably broad-spectrum of activity against *Aspergillus* and the related hyaline moulds. Their activity does, however, vary for the agents of zygomycosis, with posaconazole being the azole with the most reliable activity against this class of fungi. The echinocandin glucan synthesis inhibitors (caspofungin, FK463, and anidulafungin) possess a narrower spectrum of activity and should only be used if the infection is known to be due to *Aspergillus* spp [85, 86].
