Stage-Specific Tulane Virus Replication in Zebrafish: Permissive in Embryos, Restricted in Larvae

Human norovirus (HuNoV), the leading cause of foodborne illness in the United States and acute gastroenteritis globally, replicates in the zebrafish embryo and larvae model. However, due to challenges in obtaining well-characterized HuNoV positive stool specimens for research, demonstrating replication of Tulane virus (TuV), a surrogate of HuNoV, in the zebrafish embryo and larvae model is valuable to study HuNoV infection mechanisms and subsequent prevention and control strategies. Three nL of TuV (9 log RNA copies/mL or 7 log PFU/mL) were microinjected into either fertilized zebrafish eggs (within 4-hours post-fertilization [hpf]) or the yolk of 3-day post-fertilization larvae. Daily, 10 embryos or larvae were pooled into a single sample, with two samples collected per day up to 5 days post-infection (dpi). Viral RNA was quantified using droplet digital PCR. While TuV replicated in zebrafish embryos, with a 2-log increase by 3 dpi, no replication was observed in zebrafish larvae. Developmental regulation of sialylated glycans in zebrafish was investigated as a potential explanation for the absence of TuV replication in larvae. Zebrafish embryos express α-2,6-linked sialic acid (SA) residues, which decrease from 6 to 48 hpf, while α-2,3 sialylation increases later. Because TuV specifically binds to α-2,6-linked SA but not to α-2,3-linked SA, these developmental changes in sialylation were hypothesized to contribute to the absence of replication in larvae. To test this hypothesis, zebrafish embryos were microinjected with 3 nL of Sambucus nigra lectin (100 mg/mL), which binds α-2,6-linked SA, followed by TuV microinjection. However, lectin treatment did not inhibit replication of TuV, suggesting TuV may utilize other receptors in zebrafish embryos. While TuV replicates exclusively in zebrafish embryos, the previous reports of HuNoV replication in both embryonic and larval stages reveal potential limitations of TuV as a surrogate for evaluating prevention and control strategies against HuNoV transmission through food and environmental routes.