ANIMAL MODELS OF HUMAN DISEASE Vet Pathol 45:551562 (2008) Pathology of Experimental SARS Coronavirus Infection in Cats and Ferrets J. M. A.VAN DENBRAND, B. L. HAAGMANS, L. LEIJTEN, D.VANRIEL, B. E. E. MARTINA, A. D. M. E. OSTERHAUS,ANDT. KUIKEN Department of Virology, Erasmus Medical Center, Rotterdam, the Netherlands Abstract.The pathology of severe acute respiratory syndrome-coronavirus (SARS-CoV) infection in cats and ferrets is poorly described, and the distribution of angiotensin-converting enzyme 2 (ACE2), a receptor for SARS-CoV, in the respiratory tracts of these species is unknown. We observed SARS-CoV antigen expression and lesions in the respiratory tracts of 4 cats and 4 ferrets at 4 days postinoculation and ACE2 expression in the respiratory tracts of 3 cats and 3 ferrets without infection. All infected cats and ferrets had diffuse alveolar damage associated with SARS-CoV antigen expression. A novel SARS-CoV associated lesion was tracheo-bronchoadenitis in cats. SARS-CoV antigen expression occurred mainly in type I and II pneumocytes and serous cells of tracheo-bronchial submucosal glands of cats and in type II pneumocytes of ferrets. ACE2expressionoccurred mainly in type I andII pneumocytes,tracheo-bronchial goblet cells,serousepithelial cellsoftracheo-bronchial submucosalglandsincats, andtype IIpneumocytes and serous epithelial cells of tracheo-bronchial submucosal glands in ferrets. In conclusion, the pathology of SARS-CoV infection in cats and ferrets resembles that in humans except that syncytia and hyaline membranes were not observed. The identification of tracheo-bronchoadenitis in cats has potential implications for SARS pathogenesis and SARS-CoV excretion. Finally, these results show the importance of ACE2 expression for SARS-CoV infection in vivo: whereas ACE2 expression in type I and II pneumocytes in cats corresponded to SARS-CoV antigen expression in both cell types, expression of both ACE2 and SARS-CoV antigen in ferrets was limited mainly to type II pneumocytes. Key words:Angiotensin-converting enzyme (ACE2); cats; coronavirus; ferrets; histology; immuno- histochemistry; respiratory system; severe acute respiratory syndrome (SARS). Severeacuterespiratorysyndrome(SARS) emerged in the human population in November 2002 and spread rapidly across Asia, Europe, and North America in subsequent months.29Although the causative virus, SARS-coronavirus (SARS- CoV),5,6,19,28waseradicatedfromthehuman population by July 2003, its progenitors are likely still present in animal reservoirs21and could again cross the species barrier into humans. In total, SARS caused 774 deaths out of more than 8,000 peoplewithconfirmedinfection.Becausethe pathogenesisofSARSinhumansispoorly understood, it is difficult to develop preventive and therapeutic strategies against this disease.29 The primary lesion of SARS in humans is diffuse alveolar damage (DAD), indicating injury to the alveolar septa.4,7,12,25,27This lesion corresponds in part to the cell types in the respiratory tract in which SARS-CoV antigen has been detected: alveolar epithelial cells (primarily type II pneumocytes), bronchial epithelial cells, and alveolar macrophag- es.3,29,33,38,40Cases of longer duration (more than 10 days) demonstrated features of organizing-phase or late-stage DAD.7,27 Angiotensin-converting enzyme 2 (ACE2) has been identified as a receptor for the attachment to and uptake of SARS-CoV in host cells.20The distribution of ACE2 in human tissues corresponds largely to the cell types in which SARS-CoV replication has been observed: in addition to type II pneumocytes and bronchial epithelial cells, ACE2 expression has been observed in type I pneumocytes and endothelial cells as well as smooth muscle cells of blood vessels, but not alveolar macrophages.15,37 Since the appearance of SARS, several animal modelshavebeendevelopedforSARS-CoV infectioninhumans:SARS-CoVinfectionin 551 at UNIV OF BIRMINGHAM on March 20, Downloaded from macaques,6marmosets,10mice,8,31golden Syrian hamsters,32rats,24cats, and ferrets.22Subbarao and Roberts35reviewed the advantages and disadvan- tages of the above animal models. The limitations of rodents such as hamsters and young inbred mice are that they do not show illness35and their lung structure differs from that of the human lung;26the limitations of nonhuman primates are availability, cost, and housing.35SARS-CoV infections in cats and ferrets do not show these limitations and may therefore be valuable as animal models. Previous experiments showed that domestic cats and ferrets were susceptible to SARS-CoV infec- tion and that they were able to transmit the virus efficiently to previously uninfected sentinel animals that were housed with them.22The acute pulmo- nary lesions seen in those species were reported to be similar to those in humans and macaques, but were not described.22,36Chronic lesions in ferrets euthanized at 23 days after infection were bronchi- al and bronchiolar hyperplasia as