Coronavirus

Coronaviruses bind to host cell surface receptors, such as ACE2, through their spike proteins. The viral membrane then fuses with the host cell membrane, releasing the viral RNA into the cytoplasm. Once inside, the RNA genome is immediately translated by host ribosomes into polyproteins that initiate the infection cycle.

Viral proteases cleave the large polyproteins produced from viral RNA translation into smaller nonstructural proteins. These nonstructural proteins perform critical functions, including forming the replication-transcription complex and modifying cellular membranes into double-membrane vesicles that protect viral RNA synthesis from host defenses.

Coronavirus RNA replication occurs within double-membrane vesicles and convoluted membranes derived from the endoplasmic reticulum. The replication-transcription complex attaches to these modified compartments, which provide a protected niche for viral RNA synthesis and shield replication from host immune responses and cellular defenses.

Viral structural proteins are transported to the ER-Golgi intermediate compartment, where replicated viral RNA binds to nucleocapsid proteins. Newly formed virions assemble in this compartment, then travel in vesicles and exit the cell through exocytosis to infect neighboring cells and spread infection.

Most coronavirus infections cause mild or asymptomatic respiratory illness affecting the upper respiratory tract. However, certain strains like SARS-CoV can cause severe respiratory syndromes, including high fever, persistent cough, pneumonia, and multi-organ failure, particularly in individuals with comorbidities or weakened immune systems.

Coronaviruses spread through respiratory droplets released when infected individuals cough or sneeze. These enveloped RNA viruses cause respiratory illness ranging from mild to severe, and transmission occurs when droplets reach the respiratory tract of susceptible hosts, similar to respiratory syncytial virus.

Coronaviruses are enveloped viruses with a single-stranded, positive-sense RNA genome and helical nucleocapsid structure. Their hallmark feature is club-shaped spike glycoproteins protruding from the viral envelope, which facilitate attachment to host cells and distinguish them from other viral respiratory pathogens.