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Aspergillosis, caused by any of several species of Aspergillus, usually
manifests in immunocompromised or debilitated hosts as necrotizing
cavitary pulmonary lesions or as hematogenously disseminated foci
in multiple organs. Aspergillus can also cause
a hypersensitivity or allergic pneumonitis in immunocompetent hosts
and in patients with chronic pulmonary diseases. This is referred
to as allergic bronchopulmonary aspergillosis (ABPA) (eFig.
295.1).
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Ubiquitous in nature, Aspergillus spp are commonly
found in soil, water, and on decaying vegetation. Human exposure
to the spores of potentially pathogenic species, particularly A fumigatus, is
unavoidable. Aspergillus fumigatus has been implicated
in most of the disseminated and pulmonary infections, but A flavus and A
niger, among others, have also been recovered as pathogens. Transmission
occurs by inhalation of airborne spores that regularly contaminate
the environment; human-to-human transmission or zoonotic transmission has
not been documented. Patients with immunosuppression are at greatest
risk, especially those who are being treated for lymphoreticular
disorders and other hematologic malignancies. Because the phagocytic
functions of neutrophils and mononuclear cells are the primary immune
defense against invasive aspergillosis, Aspergillus is
a common infectious cause of death in bone marrow transplant recipients. Outbreaks
in transplant units have been epidemiologically linked to building
demolition and construction, which releases fungal spores into the
environment. There has been a significant increase in the incidence
of invasive aspergillosis over the past few decades owing to the
increasing numbers of patients undergoing transplantation, specifically
for hematologic malignancies, as well an increase in the intensity
of treatment regimens. Invasive aspergillosis in a patient without
underlying disease is infrequent, and intensive investigation for
a predisposing disorder should be undertaken.
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Clinical Manifestations
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Infection with Aspergillus can manifest as three
distinct syndromes; two types of noninvasive aspergillosis; pulmonary
aspergilloma and allergic bronchopulmonary aspergillosis (ABPA),
as well as invasive aspergillosis, either locally invasive or disseminated
disease.1
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Aspergilloma is the most common form of pulmonary aspergillosis2 and
occurs when the fungus grows as a dense mass of hyphae and tissue
debris within a preexistent pulmonary cavity caused by a concomitant
pulmonary disease such as tuberculosis, lung abscess, or bronchiectasis.
A patient with an aspergilloma may be asymptomatic and the lesion
noted on incidental radiographic examination; however, there may
be significant and life-threatening hemoptysis as a result of invasion
of local bronchial blood vessels lining the cavity.
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ABPA is a hypersensitivity reaction to fungal antigens and is
most commonly caused by A fumagatis. ABPA is seen
in patients with chronic pulmonary disease such as asthma or cystic
fibrosis. Some studies suggest that ABPA occurs in up to 15% of
patients with cystic fibrosis3 and in 7% to
14% of patients with corticosteroid dependent asthma.4 Inhalation
of fungal spores leads to hyphal colonization of the bronchopulmonary
tree resulting in mucus plugging, ...