Rising SARS-CoV-2 Seroprevalence and Patterns of Cross-Variant Antibody Neutralization in UK Domestic Cats (preprint)

Recent evidence confirming cat-to-human SARS-CoV-2 transmission has highlighted the importance of monitoring infection in domestic cats. Although the effects of SARS-CoV-2 infection on feline health are poorly characterized, cats have close contact with humans, and with both domesticated and wild animals. Accordingly, they could act as a reservoir of infection, an intermediate host and a source of novel variants. To investigate the spread of the virus in the cat population, serum samples were tested for SARS-CoV-2 antibodies by ELISA and a pseudotype-based virus neutralization assay, designed to detect exposure to variants known to be circulating in the human population. Overall seroprevalence was 3.2%, peaking at 5.3% in autumn 2021. Variant-specific neutralizing antibody responses were detected with titers waning over time. The variant-specific response in the feline population correlated with and trailed the variants circulating in the human population, indicating multiple ongoing human-to-cat spill-over events.

Respiratory disease in cats associated with human-to-cat transmission of SARS-CoV-2 in the UK (preprint)

Two cats from different COVID-19-infected households in the UK were found to be infected with SARS-CoV-2 from humans, demonstrated by immunofluorescence, in situ hybridisation, reverse transcriptase quantitative PCR and viral genome sequencing. Lung tissue collected post-mortem from cat 1 displayed pathological and histological findings consistent with viral pneumonia and tested positive for SARS-CoV-2 antigens and RNA. SARS-CoV-2 RNA was detected in an oropharyngeal swab collected from cat 2 that presented with rhinitis and conjunctivitis. High throughput sequencing of the virus from cat 2 revealed that the feline viral genome contained five single nucleotide polymorphisms (SNPs) compared to the nearest UK human SARS-CoV-2 sequence, and this human virus contained eight SNPs compared to the original Wuhan-Hu-1 reference. An analysis of the viral genome of cat 2 together with nine other feline-derived SARS-CoV-2 sequences from around the world revealed no shared cat-specific mutations. These findings indicate that human-to-cat transmission of SARS-CoV-2 occurred during the COVID-19 pandemic in the UK, with the infected cats developing mild or severe respiratory disease. Given the versatility of the new coronavirus, it will be important to monitor for human-to-cat, cat-to-cat and cat-to-human transmission.

Establishment of a reverse genetics system for SARS-CoV-2 using circular polymerase extension reaction (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been identified as the causative agent of coronavirus disease 2019 (COVID-19). While the development of specific treatments and a vaccine is urgently needed, functional analyses of SARS-CoV-2 have been limited by the lack of convenient mutagenesis methods. In this study, we established a PCR-based, bacterium-free method to generate SARS-CoV-2 infectious clones. Recombinant SARS-CoV-2 could be rescued at high titer with high accuracy after assembling 10 SARS-CoV-2 cDNA fragments by circular polymerase extension reaction (CPER) and transfection of the resulting circular genome into susceptible cells. Notably, the construction of infectious clones for reporter viruses and mutant viruses could be completed in two simple steps: introduction of reporter genes or mutations into the desirable DNA fragments (~5,000 base pairs) by PCR and assembly of the DNA fragments by CPER. We hope that our reverse genetics system will contribute to the further understanding of SARS-CoV-2.