Detection of Feline Coronavirus in Bronchoalveolar Lavage Fluid from Cats with Atypical Lower Airway and Lung Disease: Suspicion of Virus-Associated Pneumonia or Pneumonitis.

Simple Summary: Diagnosing viral pneumonia in small animals before death is uncommon, partly due to the specialized procedure needed to collect lung samples, called bronchoalveolar lavage (BAL), and the infrequent testing for viruses in these samples. Although feline coronavirus (FeCoV) infections are common in cats, it is unclear how often this virus appears in BAL fluid and its relationship with lung problems. This study reviewed 1162 clinical samples submitted for FeCoV testing, of which 25 were BAL samples from cats with atypical lower airway and lung disease. Of the BAL samples tested for FeCoV, 13% (three out of twenty-four) were positive, with no other pathogens detected, suggesting a clinical suspicion of FeCoV-associated pneumonia or pneumonitis. The cats that tested positive for FeCoV in this study appeared to have more abnormal multinucleated cells and nodular lesions in their lungs, but statistical analysis lacked significance, possibly due to the small sample size. An initial corticosteroid treatment yielded improvement of clinical signs in all the cats with suspected FeCoV-associated lung disease, but the long-term prognosis varied. These findings highlight the need for further research on the interplay between FeCoV exposure and lung responses in cats. The premortem understanding of the role of feline coronavirus (FeCoV) in the lungs of cats is limited as viruses are seldom inspected in the bronchoalveolar lavage (BAL) specimens of small animal patients. This study retrospectively analyzed the prevalence of FeCoV in BAL samples from cats with atypical lower airway and lung disease, as well as the clinical characteristics, diagnostic findings, and follow-up information. Of 1162 clinical samples submitted for FeCoV RT-nPCR, 25 were BAL fluid. After excluding 1 case with chronic aspiration, FeCoV was found in 3/24 (13%) BAL specimens, with 2 having immunofluorescence staining confirming the presence of FeCoV within the cytoplasm of alveolar macrophages. The cats with FeCoV in BAL fluid more often had pulmonary nodular lesions (66% vs. 19%, p = 0.14) and multinucleated cells on cytology (100% vs. 48%, p = 0.22) compared to the cats without, but these differences did not reach statistical significance due to the small sample size. Three cats showed an initial positive response to the corticosteroid treatment based on the clinical signs and radiological findings, but the long-term prognosis varied. The clinical suspicion of FeCoV-associated pneumonia or pneumonitis was raised since no other pathogens were found after extensive investigations. Further studies are warranted to investigate the interaction between FeCoV and lung responses in cats. [ABSTRACT FROM AUTHOR]