Protective Immunity and Persistent Lung Sequelae in Domestic Cats after SARS-CoV-2 Infection

Abstract

Severe acute respiratory syndrome coronavirus 2 readily transmits between domestic cats. We found that domestic cats that recover from an initial infection might be protected from reinfection. However, we found long-term persistence of inflammation and other lung lesions after infection, despite a lack of clinical symptoms and limited viral replication in the lungs.

Keywords: COVID-19; SARS-CoV-2; cats; coronavirus disease; lung sequelae; protective immunity; reinfection; respiratory infections; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

Comparison of histopathology between cats on day 28 after initial infection with severe acute respiratory syndrome coronavirus 2 and on day 21 after reinfection. Bronchioles and alveoli of cats (cats 1–3 in Appendix Figure 6) on day 28 after initial infection (A) and those of cats (infected cats 1–3 in Appendix Figure 6, upper half) on day 21 after reinfection (49 days after the initial infection) (B); original magnification × 20. Cats from both groups showed histiocytic bronchiolitis with occlusive plugs, peribronchiolar fibrosis, and thickening of alveolar septa. Mild acute hemorrhage was detected in affected and less affected regions of the lung on day 21 after reinfection, with a trend toward an increase compared with day 28 (severity score 1.8 + SEM 0.8 on day 21 vs. 0.3 + SEM 0.2 on day 28; p = 0.187 by unpaired t-test).

Figure 2

Timeline of severe acute respiratory syndrome coronavirus 2 infection and reinfection of cats and distribution of interstitial thickening. A) Timeline of infection and reinfection. As reported previously (1), a group of cats was inoculated with severe acute respiratory syndrome coronavirus 2 on day 0 (infected cats 1–3, upper half). A virus-naive cat was cohoused with each of the infected cats from day 1 (contact cats 1–3, lower half). The days on which infectious virus was detected in the nasal swabs are shown as red bars for each animal. In this study, we infected the cats with the same severe acute respiratory syndrome coronavirus 2 isolate at ≈4 weeks after initial infection or exposure to infected cats. After reinfection of the group shown in the upper half of the figure, no infectious virus was detected in the nasal swabs. The cats were confirmed to be seronegative before the initial infection or cohousing with infected cats, and seropositive before reinfection, on the basis of neutralization assay results. B) The distribution of interstitial thickening (interstitial pneumonia severity score) was decreased on day 21 after reinfection compared with day 28 (p = 0.041 by unpaired t-test).