Transmission and protection against re-infection in the ferret model with the SARS-CoV-2 USA-WA1/2020 reference isolate

  1. Devanshi R. Patel
  2. Cassandra J. Field
  3. Kayla M. Septer
  4. Derek G. Sim
  5. Matthew J. Jones
  6. Talia A. Heinly
  7. Elizabeth A. McGraw
  8. Troy C Sutton

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Abstract

SARS-CoV-2 has initiated a global pandemic and vaccines are being rapidly developed. Using the reference strain SARS-CoV-2 USA-WA1/2020, we evaluated modes of transmission and the ability of prior infection or vaccine-induced immunity to protect against infection in ferrets. Ferrets were semi-permissive to infection with the USA-WA1/2020 isolate. When transmission was assessed via the detection of vRNA at multiple timepoints, direct contact transmission was efficient to 3/3 and 3/4 contact animals in two respective studies, while respiratory transmission was poor to only 1/4 contact animals. To assess the durability of immunity, ferrets were re-challenged 28 or 56 days post-primary infection. Following viral challenge, no infectious virus was recovered in nasal wash samples. In addition, levels of vRNA in the nasal wash were several orders of magnitude lower than during primary infection, and vRNA was rapidly cleared. To determine if intramuscular vaccination protected ferrets against infection, ferrets were vaccinated using a prime-boost strategy with the S-protein receptor-binding domain formulated with an oil-in-water adjuvant. Upon viral challenge, none of the mock or vaccinated animals were protected against infection, and there were no significant differences in vRNA or infectious virus titers in the nasal wash. Combined these studies demonstrate that in ferrets direct contact is the predominant mode of transmission of the SARS-CoV-2 USA-WA1/2020 isolate and immunity to SARS-CoV-2 is maintained for at least 56 days. Our studies also indicate protection of the upper respiratory tract against SARS-CoV-2 will require vaccine strategies that mimic natural infection or induce site-specific immunity.

Importance

The SARS-CoV-2 USA-WA1/2020 strain is a CDC reference strain used by multiple research laboratories. Here, we show the predominant mode of transmission of this isolate in ferrets is by direct contact. We further demonstrate ferrets are protected against re-infection for at least 56 days even when levels of neutralizing antibodies are low or undetectable. Last, we show that when ferrets were vaccinated by the intramuscular route to induce antibodies against SARS-CoV-2, ferrets remain susceptible to infection of the upper respiratory tract. Collectively, these studies suggest protection of the upper respiratory tract will require vaccine approaches that mimic natural infection.

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  1. ScreenIT

    SciScore for 10.1101/2020.11.20.392381: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board StatementIACUC: All animal studies were approved by the PSU Animal Care and Use Committee under protocol no. 202001440.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variableEqual number of male and female ferrets, 24-30 weeks old (Triple F Farms, Sayre, PA) were used for all studies.
    Cell Line Authenticationnot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    S-protein RBD ELISA: To quantify anti-S protein RBD antibodies from ferret serum, 96-well ELISA plates (Nunc) were coated overnight with 2.0 ug/mL (100ng/well) of SARS-CoV-2 RBD S Protein (Sino Biological) in sodium bicarbonate buffer.
    anti-S protein RBD
    suggested: (Imported from the IEDB Cat# RBD-25E4, RRID:AB_2848097)
    Plates were washed again and incubated for 2 hours at room temperature with HRP conjugated anti-ferret goat antibody (Rockland) diluted 1:10,000 in PBST and 1% skim milk powder.
    anti-ferret goat antibody (Rockland)
    suggested: None
    Experimental Models: Cell Lines
    SentencesResources
    To assess peak titers in the nasal wash samples, 10-fold serial dilutions of virus were titrated in 96-well plates of Vero E6 cells.
    Vero E6
    suggested: RRID:CVCL_XD71)
    Software and Algorithms
    SentencesResources
    Biocontainment and Animal Care and Use: All experiments with SARS-CoV-2 were conducted in the Eva Pell Laboratory for Advanced Biological Research which is the Pennsylvania State University’s biosafety level 3 enhanced laboratory.
    Advanced Biological
    suggested: None
    Statistical analysis was performed with Prism GraphPad (v8.4.3) and p<0.05 considered statistically significant.
    GraphPad
    suggested: (GraphPad Prism, RRID:SCR_002798)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  2. Version published to 10.1101/2020.11.20.392381 on bioRxiv