Sinonasal aspergillosis (SNA) most commonly affects middle-aged dolichocephalic dogs and is characterised by a destructive rhinitis and sinusitis, in the absence of fungal deeper tissue invasion. Pathogenesis of the disease is, to date, not fully understood. An uncontrolled and detrimental inflammatory response to commensal fungal colonization of the nasal cavities and sinuses has been suggested. In humans, a role of the bacterial microbiota in the regulation of host immune responsiveness to fungi has been hypothesised. Therefore, the objective of the present study was to identify and characterise the microbiota present in nasal cavities of client-owned dogs diagnosed with SNA compared with healthy age and breed-matched non-affected dogs.

Nine large-breed dolichocephalic dogs diagnosed with SNA (6 males, 3 females, mean age 5.5 years) and 10 healthy age-and breed-matched dogs (7 males, 3 females, mean age 5 years) were included. DNA was extracted from a sterile swab introduced in the distal third of the right nasal cavity under general anaesthesia. Metagenetic analysis was performed on V1-V3 hypervariable region of 16S rDNA after total bacterial DNA extraction from nasal specimens and sequencing on a MiSeq Illumina sequencer. Taxonomical assignation and microbiota community analysis were done with MOTHUR V1.35 with an OTU clustering distance of 0.03. Differences of population abundance between groups were assessed using multiple t tests with Holm-Sidak multi-test correction (significance <0.05).

Sequencing revealed that Proteobacteria and Firmicutes were the two most predominant phyla in both groups; representing together almost 80% of the total bacterial abundance. The remaining 20% were composed of Bacteroidetes and Fusobacteria in diseased dogs, and of Actinobacteria almost exclusively in healthy dogs. At family level, a significantly higher abundance of Lactobacillaceae were found in SNA dogs, while Moraxellaceae significantly predominated in controls. Analysis of diversity metrics revealed that bacterial species richness and diversity were significantly higher in SNA dogs compared with controls.

In conclusion, results of the present study demonstrated the presence of nasal microbiota alteration in dogs affected with SNA in association with an increased bacterial diversity. However, whether such changes are a cause or a consequence of the disease is unknown and warrants further investigation.

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