Infectious droplet exposure is an inefficient route for SARS-CoV-2 infection in the ferret model.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19) in humans, has a wide host range, naturally infecting felids, canids, cervids, rodents and mustelids. Transmission of SARS-CoV-2 is universally accepted to occur via contact with contaminated secretions from the respiratory epithelium, either directly or indirectly. Transmission via droplet nuclei, generated from a cough or sneeze, has also been reported in several human and experimental animal scenarios. However, the role of droplet transmission at the human-animal interface remains to be fully elucidated. Here, the ferret infection model was used to investigate the routes of infection for the SARS-CoV-2 beta variant (B.1.351). Ferrets were exposed to droplets containing infectious SARS-CoV-2, ranging between 4 and 106 µm in diameter, simulating larger droplets produced by a cough from an infected person. Following exposure, viral RNA was detected on the fur of ferrets, and was deposited onto environmental surfaces, as well as the fur of ferrets placed in direct contact; SARS-CoV-2 remained infectious on the fur for at least 48 h. Low levels of viral RNA were detected in the nasal washes early post-exposure, yet none of the directly exposed, or direct-contact ferrets, became robustly infected or seroconverted to SARS-CoV-2. In comparison, ferrets intranasally inoculated with the SARS-CoV-2 beta variant became robustly infected, shedding viral RNA and infectious virus from the nasal cavity, with transmission to 75 % of naive ferrets placed in direct contact. These data suggest that larger infectious droplet nuclei and contaminated fur play minor roles in SARS-CoV-2 transmission among mustelids and potentially other companion animals.

Comparison of Serological Assays for the Detection of SARS-CoV-2 Antibodies.

SARS-CoV-2 virus was first detected in late 2019 and circulated globally, causing COVID-19, which is characterised by sub-clinical to severe disease in humans. Here, we investigate the serological antibody responses to SARS-CoV-2 infection during acute and convalescent infection using a cohort of (i) COVID-19 patients admitted to hospital, (ii) healthy individuals who had experienced 'COVID-19 like-illness', and (iii) a cohort of healthy individuals prior to the emergence of SARS-CoV-2. We compare SARS-CoV-2 specific antibody detection rates from four different serological methods, virus neutralisation test (VNT), ID Screen® SARS-CoV-2-N IgG ELISA, Whole Antigen ELISA, and lentivirus-based SARS-CoV-2 pseudotype virus neutralisation tests (pVNT). All methods were able to detect prior infection with COVID-19, albeit with different relative sensitivities. The VNT and SARS-CoV-2-N ELISA methods showed a strong correlation yet provided increased detection rates when used in combination. A pVNT correlated strongly with SARS-CoV-2 VNT and was able to effectively discriminate SARS-CoV-2 antibody positive and negative serum with the same efficiency as the VNT. Moreover, the pVNT was performed with the same level of discrimination across multiple separate institutions. Therefore, the pVNT is a sensitive, specific, and reproducible lower biosafety level alternative to VNT for detecting SARS-CoV-2 antibodies for diagnostic and research applications. Our data illustrate the potential utility of applying VNT or pVNT and ELISA antibody tests in parallel to enhance the sensitivity of exposure to infection.