Aspergillus fumigatus and Aspergillosis

Etiology/Bacteriology

Taxonomy

Superkingdom = Eukaryota
Kingdom = Fungi
Subkingdom = Dikarya
Phylum = Ascomycota
Subphylum = Pezizomycotina
Class = Eurotiomycetes
Subclass = Eurotiomycetidae
Order = Eurotiales
Family = Aspergillaceae
Genus = Aspergillus
Species = A. fumigatus [1]

Description

Aspergillus fumigatus, a saprophytic fungus, can opportunistically cause a multitude of diseases in humans [2]. A. fumigatus, which primarily lives in soil and decaying vegetation, can be dispersed through the air as asexual spores, known as conidia. Because of this, humans usually get infected with the fungus by inhaling these conidia. In a given day someone inhales an average of 200 A. fumigatus spores [2]. In heathy individuals, the innate immune system kills all of the conidia that the body encounters; however, in immunocompromised individuals A. fumigatus infection is a serious concern.

Invasive aspergillosis (IA), which is primarily caused by A. fumigatus, is very severe and life-threatening infectious disease [3].

Pathogenesis

Transmission

Aspergillus fumigatus is primarily transmitted through the inhalation of fungal spores, called conidia [2]. A. fumigatus conidia can be found ubiquitously in both indoor and outdoor environments, so people are continuously inhaling the fungi. The continued presence of A. fumigatus is usually not a problem; however, without proper respiratory tract immune defenses infection can occur.

Host Immune Response

Innate Immune Response

A. Fumigatus begins its life cycle with asexual reproduction, producing airborne spores, called conidia [2]. If these spores are inhaled by individual with a properly working immune system, the spores rarely make it all the way to the bronchioles and alveoli. The conidia first encounter the mucosa that lines the respiratory tract, where complement is activated. The overwhelming majority of the spores are removed via mucociliary clearance. those that survive make their way to the aveoli where they are phagocytized by aveolar macrophages, which use reactive oxidant intermediates to kill the conidia (philippe, et al).

References

1. UniProt. Taxonomy: Species Aspergillus fumigatus. Available at http://www.uniprot.org/taxonomy/746128.
2. Dagenais T and Keller N. Pathogenesis of Aspergillus fumigatus in Invasive Aspergillosis. Clin Microbial Rev. doi: 10.1128/CMR.00055-08. http://cmr.asm.org/content/22/3/447.full.
3. Tekaia F and Latge JP. Aspergillus fumigatus: saprophyte or pathogen?. Current Opinion in Microbiology. doi: 10.1016/j.mib.2005.06.017. http://www.sciencedirect.com/science/article/pii/S1369527405000925.