Abstract
BACKGROUND: The COVID-19 pandemic has caused over 776 million confirmed cases and more than 7 million deaths worldwide. In addition to humans, various animal species have exhibited natural infections, with mink being the only farmed animals consistently linked to severe illness and zoonotic transmission to humans. This study investigates histological pulmonary lesions in Danish farm mink infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), focusing on groups with different clinical signs and outcomes. RESULTS: Histopathological evaluations revealed lesions in SARS-CoV-2-positive mink with and without clinical signs of disease. The main findings in lungs from SARS-CoV-2-positive mink in all study groups were extensive respiratory epithelial damage, acute diffuse alveolar damage, and vascular lesions, including the formation of thrombi. Additionally, immunohistochemical staining confirmed the presence of viral particles primarily in the respiratory epithelia. Lymphoid cells exhibited nodular and perivascular aggregates similar to bronchus-associated lymphoid tissue in older SARS-CoV-2 infected and uninfected mink, indicating a potential age-related feature of mink lungs. CONCLUSIONS: The presence of subclinical and long-term pulmonary lesions associated with SARS-CoV-2 infections in farm mink suggests that the impact of outbreaks may be more serious than clinical signs records indicate. The current SARS-CoV-2 surveillance system on Danish mink farms does not properly address such problems and repeated outbreaks on farms could occur without detection if there are no clinical signs or increased mortality due to SARS-CoV-2. The severity of subclinical lesions reveals hidden health and welfare challenges in mink, underscoring the need for improved prevention measures, surveillance and understanding of long-term impact of SARS-CoV-2 infection in mink.