Severe acute respiratory syndrome coronavirus infection in vaccinated ferrets

Background. Development of vaccines to prevent severe acute respiratory syndrome (SARS) is limited by the lack of well-characterized animal models. Previous vaccine reports have noted robust neutralizing antibody and inflammatory responses in ferrets, resulting in enhanced hepatitis. Methods. We evaluated the humoral immune response and pathological end points in ferrets challenged with the Urbani strain of SARS-associated coronavirus (SARS-CoV) after having received formalin-inactivated whole-virus vaccine or mock vaccine. Results. Humoral responses were observed in ferrets that received an inactivated virus vaccine. Histopathological findings in lungs showed that infection of ferrets produced residual lung lesions not seen in both mock and vaccinated ferrets. SARS-CoV infection demonstrated bronchial and bronchiolar hyperplasia and perivascular cuffing in ferret lung tissue, as seen previously in infected mice. No evidence of enhanced disease was observed in any of the ferrets. All of the ferrets cleared the virus by day 14, 1 week earlier if vaccinated. Conclusions. The vaccine provided mild immune protection to the ferrets after challenge; however, there was no evidence of enhanced liver or lung disease induced by the inactivated whole-virus vaccine. The ferret may provide another useful model for evaluating SARS vaccine safety and efficacy.