Systematic Veterinary Virology

REPLICATION

• Replication occurs in the cytoplasm and is rapid. The replication cycle occurs very fast and is completed between 5-10 hours. Protein synthesis in the virus infected cell declines sharply almost to nil level and this is called Shut off.
• Since the genome is positive sense, it is immediately translated into a polyprotein, which is cleaved into enzymes required for genome replication and into structural protein by protease enzymes.
• One such product is the RNA-dependent RNA polymerase enzyme, which copies the genomic RNA to produce a (-) sense strand. This (-) sense strand replicative intermediate and from which (+) sense RNAs produced. These (+) sense RNAs are packed into the capsid. RNA is packed into preformed capsids. Hence, empty capsids (defective) are common in all Picornavirus infections. Release (in most cases) of the virus from the cytoplasm occurs when the cell lyses.
• This is a 'preprogrammed' event, which occurs a set time after the cessation of 'housekeeping' macromolecular synthesis at shutoff. The sequence of events that take place in a cell infected with FMDV is as below.