Last updated on:November 20th, 2023
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Aspergillosis refers to a variety of illnesses caused by the fungal species of Aspergillus (most commonly A. fumigatus, A. flavus, A. niger, and A. terreus). Lung, skin, and central nervous system are the organs mainly involved. The manifestation of the disease depends on the host's immune status and the pulmonary structure since the species are ubiquitous in nature, and inhalation of infectious conidia (spores) is a frequent event.
The cells of the innate immunity (epithelial alveolar cells and macrophages) normally clear the inhaled Aspergillus conidia. These cells produce mediators that are able to recruit neutrophils and activate cellular immunity in order to kill the potentially invasive fungus forms (hyphae). The suppression of these mechanisms, including the suppression of the T cell responses, plays a determinant role in the occurrence of the disease and the type of the disease. Infection can disseminate to other organs.
Classic risk factors include severe and prolonged neutropenia, transplantations, receipt of high doses of glucocorticoids, hematological malignancies, chemotherapy, advanced AIDS and other conditions or use of other drugs that lead to chronically impaired cellular immune responses. Viral infections such as SARS CoV-2 and influenza are considered risk factors in the setting of respiratory failure in the ICUs, maybe due to the epithelial airway injury that facilitates Aspergillus colonization and invasion. Other risk factors include the presence of chronic lung diseases, such as chronic obstructive pulmonary disease.
Aspergillosis most frequently affects the lungs since the respiratory tract is the main portal of entry. Typical forms are:
COVID-19 associated pulmonary aspergillosis (CAPA)
CAPA is characterized by pulmonary infiltrates, preferably documented by chest CT, or cavitating infiltrate in patients with COVID-19 pneumonia needing intensive care and microbiological evidence of fungal elements in clinical specimens (bronchoalveolar lavage, sputum, serum, plasma).
Central nervous system infection
Aspergillus spp can disseminate beyond the respiratory tract to multiple different organs, including the brain. Typical patterns observed in brain imaging are cerebral abscesses or cortical and subcortical infarction. The prognosis is poor.
Cutaneous aspergillosis may occur either from direct inoculation of spores, usually in the presence of trauma, or from contiguous extension or bloodborne spread.