Astroviruses use mucus secretion as a novel form of viral egress

Viruses rely on coordinated host pathways to exit the cell and propagate infection. We have come to appreciate that non-enveloped enteric viruses can use both lytic and non-lytic strategies to exit host cells. However, it remains unclear how astroviruses, a major causative agent of pediatric diarrhea, facilitate this final step in their replication cycle. Because astroviruses infect small intestinal goblet cells, we investigated whether mucus secretion could enable a pathway of non-lytic viral egress. Using the murine astrovirus model, we found that virus release co-occurred almost exclusively with mucus secretion from goblet cells. At the tissue level, mucus secretion also correlated with infection kinetics, characterized by a return to baseline secretion during viral clearance. Further, disruption of mucin biosynthesis reduced viral shedding, and stimulating mucus secretion with carbachol increased viral release. To examine this pathway with human astrovirus, we established a new infection model in LS174T goblet cells. We observed that human astrovirus colocalized with MUC2 within the cell and with purified mucin granules. Stimulating cells with carbachol enhanced mucus and virus release, which could be blocked by the addition of a muscarinic receptor antagonist. Further, we found that blocking intracellular calcium, which drives mucin granule exocytosis, also reduced virus release. Together, these findings demonstrate that mucus secretion is a novel form of non-lytic enteric viral egress, which deepens our understanding of the astrovirus replication cycle and may hold clues to understanding its pathogenesis.