Physical Address

304 North Cardinal St.
Dorchester Center, MA 02124

Aspergillus


The aspergilli are ubiquitous fungi whose normal ecological niche is that of a soil saprophyte that recycles carbon and nitrogen. The genus Aspergillus contains approximately 250 species, but most human disease is caused by Aspergillus fumigatus , A. flavus , A. niger , A. terreus, and A. nidulans . Invasive disease is most commonly caused by A. fumigatus . Aspergillus reproduces asexually via production of spores (conidia). Most cases of Aspergillus disease (aspergillosis) are due to inhalation of airborne conidia that subsequently germinate into fungal hyphae and invade host tissue. People are likely exposed to conidia on a daily basis. When inhaled by an immunocompetent person, conidia are rarely deleterious, presumably because they are efficiently cleared by phagocytic cells. Macrophage- and neutrophil-mediated host defenses are required for resistance to invasive disease.

Aspergillus is a relatively unusual pathogen in that it can create very different disease states depending on the host characteristics, including allergic (hypersensitivity), saprophytic (noninvasive), chronic, or invasive disease. Immunodeficient hosts are at risk for invasive disease, whereas immunocompetent atopic hosts tend to develop allergic disease. Disease manifestations include primary allergic reactions; colonization of the lungs or sinuses; localized infection of the lung or skin; chronic infection of the lung; invasive pulmonary disease; or widely disseminated disease of the lungs, brain, skin, eye, bone, heart, and other organs. Clinically, these syndromes often manifest with mild, nonspecific, and late-onset symptoms, particularly in the immunosuppressed host, complicating accurate diagnosis and timely treatment.

Allergic Disease (Hypersensitivity Syndromes)

William J. Steinbach

Keywords

  • allergic bronchopulmonary aspergillosis

  • asthma

Asthma

Attacks of atopic asthma can be triggered by inhalation of Aspergillus conidia, producing allergic responses and subsequent bronchospasm. Exposure to fungi, especially Aspergillus , needs to be considered as a trigger in a patient with an asthma flare, especially in those patients with severe or recalcitrant asthma.

Extrinsic Alveolar Alveolitis

Extrinsic alveolar alveolitis is a hypersensitivity pneumonitis that occurs due to repetitive inhalational exposure to inciting materials, including Aspergillus conidia. Symptoms typically occur shortly after exposure and include fever, cough, and dyspnea. Neither blood nor sputum eosinophilia is present. Chronic exposure to the triggering material can lead to pulmonary fibrosis.

Allergic Bronchopulmonary Aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) is a hyper-sensitivity disease resulting from immunologic sensitization to Aspergillus antigens. It is primarily seen in patients with asthma or cystic fibrosis. Inhalation of conidia produces non-invasive colonization of the bronchial airways, resulting in persistent inflammation and development of hypersensitivity inflammatory responses. Disease manifestations are due to abnormal immunologic responses to A. fumigatus antigens and include wheezing, pulmonary infiltrates, bronchiectasis, and even fibrosis.

There are 8 primary diagnostic criteria for ABPA: episodic bronchial obstruction, peripheral eosinophilia, immediate cutaneous reactivity to Aspergillus antigens, precipitating IgE antibodies to Aspergillus antigen, elevated total IgE, serum precipitin (specific IgG) antibodies to A. fumigatus, pulmonary infiltrates, and central bronchiectasis. Secondary diagnostic criteria include repeated detection of Aspergillus from sputum by identification of morphologically consistent fungal elements or direct culture, coughing brown plugs or specks. Radiologically, bronchial wall thickening, pulmonary infiltrates, and central bronchiectasis can be seen.

Treatment depends on relieving inflammation via an extended course of systemic corticosteroids. Addition of oral antifungal agents, such as itraconazole or voriconazole, is used to decrease the fungal burden and diminish the inciting stimulus for inflammation. Because disease activity is correlated with serum IgE levels, these levels are used as one marker to define duration of therapy. An area of research interest is the utility of anti-IgE antibody therapy in the management of ABPA.

Allergic Aspergillus Sinusitis

Allergic Aspergillus sinusitis is thought to be similar in etiology to ABPA. It has been primarily described in young adult patients with asthma and may or may not be seen in combination with ABPA. Patients often present with symptoms of chronic sinusitis or recurrent acute sinusitis, such as congestion, headaches, and rhinitis, and are found to have nasal polyps and opacification of multiple sinuses on imaging. Laboratory findings can include elevated IgE levels, precipitating antibodies to Aspergillus antigen, and immediate cutaneous reactivity to Aspergillus antigens. Sinus tissue specimens might contain eosinophils, Charcot-Leyden crystals, and fungal elements consistent with Aspergillus species. Surgical drainage is an important aspect of treatment, often accompanied by courses of either systemic or inhaled steroids. Use of an antifungal agent may also be considered.

Bibliography

  • Knutsen AP, Bush RK, Demain JG, et. al.: Fungi and allergic lower respiratory tract diseases. J Allergy Clin Immunol 2012; 129: pp. 280-291.
  • Knutsen AP, Slavin RG: Allergic bronchopulmonary aspergillosis in asthma and cystic fibrosis. Clin Dev Immunol 2011; 2011: pp. 843763.

Saprophytic (Noninvasive) Syndromes

William J. Steinbach

Keywords

  • chronic cavitary aspergillosis

  • aspergilloma

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here

Related Posts