RNAviruksiin

RNAviruksiin are viruses whose genomes are composed of RNA. They form a large and diverse group that includes positive-sense single-stranded RNA (+ssRNA), negative-sense single-stranded RNA (-ssRNA), and double-stranded RNA (dsRNA). Their genomes can be nonsegmented or segmented, and they may be enveloped or non-enveloped, with a wide range of sizes and morphologies from icosahedral to helical and filamentous.

Replication relies on RNA-dependent RNA polymerases, enzymes that copy RNA without a DNA intermediate. Positive-sense RNA viruses can translate their genome directly into proteins, while negative-sense RNA viruses carry their polymerase in the virion and must transcribe mRNA first. Double-stranded RNA viruses use their dsRNA genomes for transcription and replication in specialized cytoplasmic compartments. Retroviruses (class VI) use reverse transcriptase to convert RNA into DNA, which integrates into the host genome and serves as a template for transcription.

Most RNAviruksiin replicate in the cytoplasm; some, such as influenza viruses, replicate in the nucleus. They exhibit high mutation rates due to limited proofreading by their polymerases, which accelerates antigenic drift and shift in some lineages. Exceptions exist, notably coronaviruses, which possess a proofreading exonuclease that moderates their mutation rate.

Clinically important families include Picornaviridae (rhinoviruses, enteroviruses), Orthomyxoviridae (influenza), Coronaviridae (SARS-CoV-2, common cold coronaviruses), Flaviviridae (Dengue, Zika), Caliciviridae (noroviruses), Reoviridae (rotaviruses), Rabdoviridae (rabies), Paramyxoviridae (measles, mumps), and Filoviridae (Ebola). RNAviruksiin pose ongoing public health challenges due to rapid evolution, diverse transmission routes, and potential for zoonotic spillover, requiring vaccines and targeted antivirals to mitigate disease impact.