Astroviruses are human pathogens with emerging disease associations, including the recent recognition of their capacity to cause meningoencephalitis. Astrovirus VA1 is the most commonly identified astrovirus genotype from cases of human encephalitis, but it is unknown what percentage of the human population has neutralizing antibodies to VA1.
Background Since their original isolation from human stool samples in 1975, astroviruses have been assumed to be pathogens exclusive to the gastrointestinal tract. However, astroviruses have been recently identified from brain tissue of humans and other mammals suffering from neurological diseases, suggesting that members of this family of viruses have a previously unrecognized neurotropism. One human astrovirus genotype, astrovirus VA1/HMO-C (VA1) is the most frequently identified astrovirus from cases of human encephalitis. We previously described the ability of several cell lines, including Caco-2, A549, and HEK293, to support VA1 growth in cell culture. Our goals were to develop cell culture and animal models to study the pathogenic potential of VA1. Methods VA1 was inoculated into primary astrocytes, primary neurons, and SK-N-SH cells in tissue culture. Viral RNA was measured in multistep growth curves by qRT-PCR, capsid was detected by immunofluorescence, and infectious titer was measured by a TCID50 assay. For development of an in vivo model of infection, mice were inoculated with VA1 with simultaneous intracranial, intraperitoneal, intravenous, and oral gavage inoculations with a VA1 stock. Mice were sacrificed 7 days after inoculation, RNA extracted from tissues, and viral load quantified by qRT-PCR. Tissue was also processed for histology and staining with hematoxylin and eosin. Primary human cardiac endothelial and myocytes were also inoculated with VA1 and viral RNA was measured in multistep growth curves by qRT-PCR. Results We detected the completion of the full VA1 lifecycle in primary astrocytes and SK-N-SH cells with >100-fold increase in viral RNA in a multistep growth curve, detection of intracellular viral capsid, and a >100-fold increase in the infectious titer. These results support the neurotropic potential of VA1. In the development of a mouse model of VA1 infection, we detected the virus in the brain tissue of mice 7 days after inoculation. Unexpectedly, we detected the highest titer of VA1 in heart tissue, which was associated with histological evidence of myocarditis. Furthermore, we demonstrated VA1 can replicate in primary human cardiac endothelial cells but not in primary human cardiac myocytes. Conclusions Our data demonstrate that astroviruses have tissue tropisms outside of the gastrointestinal tract. We provide the first demonstration that cultured neural-derived cells can support infection and replication of astroviruses, providing a model for studying the neuropathogenic potential of VA1. Furthermore, we have identified a novel cardiotropism for VA1, raising the possibility that VA1 may contribute to human cardiac diseases currently without an ascribed etiology.
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