Human noroviruses (HuNoVs) are the most common cause of foodborne illness, with a societal cost of $60 billion and 219,000 deaths/year. The lack of robust small animal models has significantly hindered the understanding of norovirus biology and the development of effective therapeutics. Here we report that HuNoV GI and GII replicate to high titers in zebrafish (Danio rerio) larvae; replication peaks at day 2 post infection and is detectable for at least 6 days. The virus (HuNoV GII.4) could be passaged from larva to larva two consecutive times. HuNoV is detected in cells of the hematopoietic lineage and the intestine, supporting the notion of a dual tropism. Antiviral treatment reduces HuNoV replication by >2 log₁₀, showing that this model is suited for antiviral studies. Zebrafish larvae constitute a simple and robust replication model that will largely facilitate studies of HuNoV biology and the development of antiviral strategies. Human norovirus (HuNoV) is the number one agent of viral gastroenteritis worldwide. It can infect people of all age groups, resulting in 700 million infections and 219,000 deaths each year. Outbreaks of acute HuNoV gastroenteritis occur often, but chronic infections also happen in people with immune deficiencies. Despite its clinical relevance, studying the virus has been a decades-long challenge because no simple and efficient cultivation system existed. This has recently started to change; we here contribute with an important step forward by establishing an in vivo model system to study HuNoV replication using zebrafish larvae. We inject a HuNoV in the yolk (food reserve) of 3-day-old zebrafish larvae, which results in high virus titers up to 6 days after inoculation. We could detect the virus in the tissues of the infected larvae by a variety of techniques including histology, which showed us in which organs the virus is present. Importantly, by adding an antiviral to the water in which the larvae swim, we could significantly reduce the virus levels in the larvae. This means that testing small molecules and developing the first antiviral therapy for HuNoV will be much easier from hereon.

A safe and highly efficient antiviral is needed for the prophylaxis and/or treatment of viral diarrhea. We here demonstrate the in vitro antiviral activity of four 2'-C-methyl nucleoside analogues against noro-, rota-, and sapoviruses. The most potent nucleoside analogue, 7-deaza-2'-C-methyladenosine, inhibits replication of these viruses with a 50% effective concentration < 5 µM. Mechanistically, we demonstrate that the 2'-C-methyl nucleoside analogues act by inhibiting transcription of the rotavirus genome. This provides the first evidence that a single viral-diarrhea-targeted treatment can be developed through a viral-polymerase-targeting small molecule.

Human noroviruses (HuNoVs) are an important cause of epidemic and endemic acute gastroenteritis worldwide; annually about 700 million people develop a HuNoV infection resulting in ∼219,000 deaths and a societal cost estimated at 60 billion US dollars ¹ . The lack of robust small animal models has significantly hindered the understanding of norovirus biology and the development of effective therapeutics against HuNoV. Here we report that HuNoV GI and GII replicate to high titers in zebrafish ( Danio rerio ) larvae; replication peaks at day 2 post infection and is detectable for at least 6 days. HuNoV is detected in cells of the hematopoietic lineage, the intestine, liver and pancreas. Antiviral treatment reduces HuNoV replication by >2 log ₁₀ , showing that this model is suited for antiviral studies. Downregulation of fucosyltransferase 8 (fut8) in the larvae reduces HuNoV replication, highlighting a common feature with infection in humans. Zebrafish larvae constitute a simple and robust replication model that will largely facilitate studies of HuNoV biology and the development of antiviral strategies.

Viral gastroenteritis is an important cause of morbidity and mortality worldwide, being particularly severe for children under the age of five. The most common viral agents of gastroenteritis are noroviruses, rotaviruses, sapoviruses, astroviruses and adenoviruses, however, no specific antiviral treatment exists today against any of these pathogens. We here discuss the feasibility of developing a broad-spectrum antiviral treatment against these diarrhea-causing viruses. This review focuses on the viral polymerase as an antiviral target, as this is the most conserved viral protein among the diverse viral families to which these viruses belong to. We describe the functional and structural similarities of the different viral polymerases, the antiviral effect of reported polymerase inhibitors and highlight common features that might be exploited in an attempt of designing such pan-polymerase inhibitor.

Acute gastroenteritis caused by virus has a major impact on public health worldwide in terms of morbidity, mortality, and economic burden. The main culprits are rotaviruses, noroviruses, sapoviruses, astroviruses, and enteric adenoviruses. Currently, there are no antiviral drugs available for the prevention or treatment of viral gastroenteritis. Here, we describe the antivirals that were identified as having in vitro and/or in vivo activity against these viruses, originating from in silico design or library screening, natural sources or being repurposed drugs. We also highlight recent advances in model systems available for this (hard to cultivate) group of viruses, such as organoid technologies, and that will facilitate antiviral studies as well as fill some of current knowledge gaps that hamper the development of highly efficient therapies against gastroenteric viruses.