Mouse Norovirus (IMAGE) National Institutes of Natural Sciences Caption Mouse norovirus has two capsid structures (type A and type B). Type A particles propagate about 4 hours faster than type B particles (bottom). Credit Kazuyoshi Murata Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.