Taxonomy
- Kingdom: Fungi
- Phylum: Ascomycota
- Class: Eurotiomycetes
- Order: Eurotiales
- Family: Trichocomaceae
- Genus: Aspergillus
- Species: A. felis
Description
Aspergillus felis is a filamentous, mold species within the genus Aspergillus. It was formally described in 2016 following the isolation of thermotolerant strains from clinical specimens of cats with invasive aspergillosis. Morphologically, colonies on standard mycological media are typically green to bluish‑green, producing conidial heads characteristic of the Aspergillus genus. Conidia are smooth‑walled, globose to subglobose, and range from 3–5 µm in diameter. Microscopic features include biseriate phialides and vesicles that are globose to subglobose.
Ecology and Distribution
The natural environmental niche of A. felis is not fully characterized, but it is presumed to be present in soil and organic debris, similar to other Aspergillus species. The species has been isolated primarily from clinical samples rather than environmental surveys, suggesting a possible opportunistic association with mammalian hosts.
Pathogenicity and Clinical Significance
Aspergillus felis is recognized as an opportunistic pathogen, especially in felines (domestic cats) but has also been reported in dogs, horses, and, rarely, immunocompromised humans. Infections are typically invasive, affecting the respiratory tract, sinuses, or disseminating to other organs. Clinical manifestations in cats include chronic rhinosinusitis, orbital cellulitis, and osteomyelitis of facial bones. The species displays variable susceptibility to antifungal agents; in vitro testing often shows reduced susceptibility to azoles (e.g., itraconazole, voriconazole) compared with A. fumigatus, making therapeutic management challenging.
Laboratory Identification
Accurate identification of A. felis relies on a combination of phenotypic observation and molecular methods. Sequencing of the internal transcribed spacer (ITS) region, β‑tubulin (benA), and calmodulin (cmdA) genes distinguishes A. felis from closely related cryptic species within the A. fumigatus complex. Matrix‑assisted laser desorption/ionization time‑of‑flight (MALDI‑TOF) mass spectrometry databases that include reference spectra for A. felis can also aid rapid identification.
Epidemiology
Since its description, case reports of A. felis infection have been limited but geographically diverse, with documented instances in Europe, North America, and Oceania. The true prevalence is uncertain, partly due to the need for specialized molecular diagnostics to differentiate it from other Aspergillus spp.
Therapeutic Considerations
Management of A. felis infections generally involves prolonged antifungal therapy, often employing combination regimens (e.g., voriconazole plus terbinafine) based on susceptibility testing. Surgical debridement may be necessary for localized disease. Ongoing monitoring of therapeutic response is essential due to the potential for drug resistance.
Research and Knowledge Gaps
Key areas requiring further investigation include the environmental reservoir of A. felis, its full host range, mechanisms underlying reduced azole susceptibility, and optimal therapeutic protocols. Expanded surveillance using molecular diagnostics will improve understanding of its epidemiology and clinical impact.