Other Positive-Strand RNA Viruses

Three miscellaneous positive-strand RNA viruses are described briefly with an emphasis on the genome structure: caliciviruses, togaviruses, and coronaviruses. Unlike those described in the two preceding chapters, these RNA viruses possess one or more subgenomic RNAs, besides the full-length genomic RNA. These subgenomic RNAs are all positioned to the 3′ side of the RNA genome and encode structural proteins. Importantly, viruses belonging to these three RNA virus families have become a global public health concern. Noroviruses, a prototype of calicivirus, are responsible for almost all viral gastroenteritis outbreaks worldwide. Moreover, some newly emerging viruses belong to togaviruses and coronaviruses. Chikungunya virus, an emerging virus that caused an outbreak in Africa during 2004–2006, belongs to the togavirus family. Severe acute respiratory syndrome (SARS) coronavirus and Middle-East respiratory syndrome (MERS) coronavirus, which caused 2003 SARS outbreak in China and 2014 MERS outbreak in the Middle East, belong to the coronavirus family.