Exploring Zebrafish Larvae as a COVID-19 Model: Probable Abortive SARS-CoV-2 Replication in the Swim Bladder.

Valerio Laghi,Veronica Rezelj,Bruno Da Costa,Pierre Boudinot,Irene Salinas,Marco Vignuzzi,Jean-Pierre Levraud,Georges Lutfalla,Laurent Boucontet,Maxence Frétaud

doi:10.3389/fcimb.2022.790851

Abstract

Animal models are essential to understanding COVID-19 pathophysiology and for preclinical 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, or bloodstream, resulted in a rapid decrease of SARS-CoV-2 RNA in wild-type larvae. However, when the virus was inoculated in the swim bladder, viral RNA stabilized after 24 h. By immunohistochemistry, epithelial cells containing SARS-CoV-2 nucleoprotein were observed in the swim bladder wall. Our data suggest an abortive infection of the swim bladder. In some animals, 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. A 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.

Highlights

The COVID-19 pandemic has taken an enormous toll worldwide, in both human and economic losses
SARS-CoV-2 Replicates in Zebrafish Larvae Only When Injected in the Swim Bladder
We first tested if an early strain of SARS-CoV-2 would replicate in wild-type zebrafish larvae after bath exposure

Summary

Introduction

The COVID-19 pandemic has taken an enormous toll worldwide, in both human and economic losses. Animal models play a central role during any pandemic since they are essential to analyzing pathology, transmission, and test vaccines and drugs. The most widely used model for host–pathogen studies, require a transgene-mediated expression of human angiotensinconverting enzyme 2 (hACE2) to be infected (Lutz et al, 2020), some recent variants replicate to a significant extent in wild-type mice (Montagutelli et al, 2021). All these models have several advantages and disadvantages. We test if zebrafish larvae can be added to the list of suitable animal models for the study of COVID-19

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Conclusion