Exploring zebrafish larvae as a COVID-19 model: probable SARS-COV-2 replication in the swim bladder

• Published in: bioRxiv
• Main Authors: Laghi, Valerio, Rezelj, Veronica, Boucontet, Laurent, Frétaud, Maxence, Bruno Da Costa, Boudinot, Pierre, Salinas, Irene, Lutfalla, Georges, Vignuzzi, Marco, Levraud, Jean-Pierre
• Format: Paper
• Language: English
• Published: Cold Spring Harbor Cold Spring Harbor Laboratory Press 10.10.2021
• Subjects: ACE2; Angiotensin-converting enzyme 2; Animal models; Coronaviruses; COVID-19; Danio rerio; Embryos; Immunohistochemistry; Infectivity; Interferon; Larvae; Microinjection; Pericardium; Replication; Severe acute respiratory syndrome coronavirus 2; Swim bladder; Ventricle; Ventricles (cerebral)
• DOI: 10.1101/2021.04.08.439059

Animal models are essential to understand COVID-19 pathophysiology and for pre-clinical assessment of drugs and other therapeutic or prophylactic interventions. We explored the small, cheap and transparent zebrafish larva as a potential host for SARS-CoV-2. Bath exposure, as well as microinjection in the coelom, pericardium, brain ventricle, bloodstream, or yolk, did not result in detectable SARS-CoV-2 replication in wild-type larvae. However, when the virus was inoculated in the swim bladder, a modest increase in viral RNA was observed after 24 hours, suggesting a successful infection in some animals. This was confirmed by immunohistochemistry, with cells positive for SARS-CoV-2 nucleoprotein observed in the swim bladder. Several variants of concern were also tested with no evidence of increased infectivity in our model. Low infectivity of SARS-CoV-2 in zebrafish larvae was not due to the host type I interferon response, as comparable viral loads were detected in type I interferon-deficient animals. Mosaic overexpression of human ACE2 was not sufficient to increase SARS-CoV-2 infectivity in zebrafish embryos or in fish cells in vitro. In conclusion, wild-type zebrafish larvae appear mostly non-permissive to SARS-CoV-2, except in the swim bladder, an aerial organ sharing similarities with the mammalian lung. Competing Interest Statement The authors have declared no competing interest. Footnotes * Confirmation of presence of infected cells in the swim bladder by whole-mount immunohostochemistry (figure 5, movie S1) Test of several variants of SARS-CoV-2 (Figure 6) Checking if overexpression of hACE2 allowed infection of a fish cell line in vitro (Figure S5) * https://doi.org/10.5281/zenodo.4672028