research highlights

Animal models of disease A fshy option for human norovirus research Van Dycke, J., et al. PloS Pathog 15, e1008009 (2019)

Norovirus may be the leading global cause passage, much smaller inoculation volumes, of foodborne illness—the highly contagious etc—but not all. The fish model involves virus triggers acute gastroenteritis in a non-physiological route of inoculation almost 700 million people annually and requiring a high titer stool sample, and contributes to 200,000 deaths—but it’s there’s no ability to generate a virus stock proven a tricky bug to study. It can be a from the fish, she noted. “Given the tools challenge to cultivate in the lab relative to available for the zebrafish model though, other viruses, explains pharmacist-turned- new basic science advances will surely follow biologist Joana Rocha-Pereira of KU Leuven from this discovery and that is always a win in Belgium; until the 1990s, it was difficult in my opinion. So I am very excited about to even detect in the first place. Since then, this finding!” researchers have gotten a handle on its A new study reveals that human norovirus Rocha-Pereira says the lab is already epidemiology and physical structure, but can infect and replicate within larval zebrafish. using the model for antiviral drug testing. gaps remain in our basic understanding of Credit: Paulo Oliveira / Alamy Stock Photo “Being a vertebrate model but still very, very norovirus biology, she says. What are its simple, it can be very powerful,” she says. receptors in its host? How does it replicate “It’s something you can put inside a 96 well and come to infect immune cells, in initially targets the enteric system, delivery plate...That’s almost as simple as running an addition to enteric ones? via the yolk, which feeds the larvae in those in vitro experiment.” But rather than cells, Answering those questions has been early developmental days, seemed the most it’s a whole organism being studied. Because limited by a dearth of animal options analogous option to mimic the food-borne it’s so very small, only small amounts of new in which to model human norovirus route by which humans become infected, drugs need to be synthesized for preliminary infection—particularly small animals Rocha-Pereira says. Given that they were testing; that can save time, money, and that can be used in larger numbers and at working with a virus capable of infecting effort, while garnering additional biological less cost than gnotobiotic pigs or calves. humans, they also had to figure out the detail at earlier time points relative to typical Rocha-Pereira had been working with most efficient way to inject many, many pipelines involving rodents, she says. a mouse model, but one infected with miniscule fish within the confines of a Beyond drug screening, the many a murine-specific norovirus; studying laminar flow cabinet; a microscope with a tools to make any number of different that surrogate viral form sufficed for a large screen helped. transgenic zebrafish lines might also help while but, with an eye towards moving Although the fish did not become visible the researchers more closely follow the preclinical drug candidates along the sick, human norovirus—of several different virus within the transparent larvae. “If we testing pipeline, she wanted to work with viral genotypes—did replicate within the want to look at the role of macrophages for human norovirus itself. Then one day, she larvae, peaking after two days but remaining example, there are transgenic lines that have was introduced to zebrafish. detectable for about a week. The team fluorescent macrophages,” she says. After Another group at KU Leuven was observed increased expression in several infection, what those macrophages do in using larval zebrafish to study epilepsy, genes involved with the innate immune response can easily be observed in the fish but a look into the literature revealed system, and the virus was also detected under a microscope. “That’s very powerful,” infection models of human influenza, in other tissues. These included caudal she says. “It’s not so easy to do with other chikungunya, and herpes simplex—three hematopoietic tissue. A broad-spectrum furry animals.” very different viruses with very different antiviral treatment, meanwhile, reduced The fish indeed won’t answer every means of infection and replication, she viral replication. human norovirus question, but Rocha- says. Human norovirus seemed worth a “I think this is a great advance that has Pereira is excited to move forward with the try—and it worked. Writing in the journal clear translational implications,” commented new model. “Finally, I can work with the PloS Pathogens, Rocha-Pereira and her Christiane Wobus from the University real thing,” she says. “We are working on colleagues describe their larval zebrafish of Michigan Medical School, who has the human viruses that are actually making model of human norovirus infection. developed a human norovirus mouse people sick—it’s not some lab-adapted There were number of practical model (Wobus has collaborated with the adapted strain people use in cell cultures.” challenges along the way to developing the KU Leuven group in the past but was not Stomach flu research might have a fishy model. There was the question of how to involved in the current zebrafish work). She future. deliver the virus itself. As it can be difficult cautions, however, that no model is perfect; to gavage such small animals, the team the zebrafish overcomes some of the issues Ellen P. Nef decided to inject stool samples from human with human norovirus mouse model—such norovirus patients into the egg yolk of three as infection with multiple viral genotypes, Published online: 14 October 2019 day post-fertilization zebrafish; as norovirus larger viral increases over time, ability to https://doi.org/10.1038/s41684-019-0427-2

Lab Animal | VOL 48 | NOVEMBER 2019 | 329–334 | www.nature.com/laban 329