#51: Neurotropic Astrovirus-VA1: Identifying the distinctions from classical genotypes

Background Human astroviruses (HAstV) are a leading cause of acute gastroenteritis in children, particularly those under the age of 2 or with immunosuppressive conditions. Indeed, our studies suggest that children with hematological malignancies are at high risk of infection. However, it has become increasingly clear that HAstV infections can also be associated with respiratory and even central nervous system (CNS) diseases. In the last decade, there have been at least 12 cases of astrovirus-induced CNS disease resulting in encephalitis and meningitis, including 2 St Jude patients. The CNS-associated infections are overwhelmingly fatal and are primarily caused by a novel astrovirus genotype, VA1, that is genetically more similar to animal astroviruses that also induce CNS-associated infections. The recent ability to propagate the VA1 strain in cell lines affords us the opportunity to better understand VA1 infection and how it compares to the better-studied HAstV1 strain. Methods Viral kinetics were determined by infection of human intestinal adenocarcinoma Caco-2 cells with either HAstV1 or VA1 and monitored for 24 hours post-infection (hpi). Infected cells were identified via immunofluorescent microscopy using antibodies against double-stranded RNA and viral capsid. Epithelial permeability of astrovirus-infected Caco-2 cells was measured using transepithelial electrical resistance (TER) and monitored for 24hpi. Nitazoxanide efficacy was identified by immunofluorescent analysis as described previously. Results Our findings demonstrate that HAstV1 and VA1 replicate in intestinal epithelial cells without inducing cell death or a pro-inflammatory cytokine response. However, these two strains have distinct replication kinetics. VA1 appears to have an ~8 hour lag in the expression of dsRNA and capsid protein compared to HAstV1 and does not require exogenous proteases to process the viral outer coat (capsid) protein, Additionally, we demonstrated that the increase in epithelial barrier permeability associated with HAstV1-infection is not found in VA1-infected cells, which is intriguing and may explain why HAstV1 is more likely to cause diarrhea. Of clinical importance, we have revealed a similar susceptibility of VA1 to the antiviral drug, nitazoxanide, which we have recently demonstrated its effectiveness inhibiting classical HAstV strains. Conclusion Overall, our studies highlight that VA1 pathogenesis is distinct from HAstV1, which could explain the differences in vivo. Future studies will be necessary to investigate viral replication and pathogenesis in distinct neuronal cells and in vivo.