Canine idiopathic pulmonary fibrosis (CIPF) is a progressive parenchymal lung disease of unknown origin and poorly understood pathophysiology that mainly occurs in old West Highland white terriers (WHWTs). Computed tomographic and histopathological findings of CIPF share characteristics of both human usual intestinal pneumonia (UIP) (typical pattern of IPF in humans) and non-specific interstitial pneumonia (NSIP) patterns. In humans, a NSIP pattern is commonly observed in hypersensitivity pneumonitis. This inflammatory pulmonary syndrome results from sensitization to inhaled antigens such as fungal particles and can cause irreversible lung fibrosis in chronic stages. Given that no aetiologies have been identified for CIPF, the objective of this study was to investigate a potential fungal cause. A conventional pan-fungal PCR assay targeting the conserved rDNA gene internal transcribed spacer (ITS) regions of fungi, using two primer pairs (ITS1-ITS2, ITS1-ITS4) was performed using DNA extracted from lung tissue samples from WHWTs affected with CIPF (n=26) and age-matched unaffected controls (n=14). DNA of soil Aspergillus fumigatus isolates were included as positive controls. Water samples were tested as negative controls. Additionally, serum samples from 8 WHWTs affected with CIPF and 8 age-matched unaffected WHWTs were tested for precipitins against 10 species of environmental fungus using electrosyneresis on cellulose acetate. Fungal ITS1-ITS2 and ITS1-ITS4 sequences were not amplified from any lung sample, suggesting that invasive fungal infection or heavy colonization is unlikely in CIPF. On the other hand, results of the serological assay revealed the presence of ≥2 arcs of precipitins (indicative of a positive result) in 55 of the 160 reactions tested (35 positive results in CIPF population vs. 20 in controls, p=0.013), supporting an increased prevalence of environmental fungal exposure in CIPF dogs compared with controls. For Lichtheimia corymbifera, a commonly involved antigen in human farmer's lung hypersensitivity pneumonitis, the number of precipitin arcs was significantly higher in CIPF dogs in comparison with controls (p=0.04). Whether this finding reflects a lung sensitization to fungal allergens and is involved in the pathogenesis of CIPF warrants further investigation.

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