Systematic Veterinary Virology

REPLICATION

• Entry of avian influenza virus into the cell is facilitated by binding of the HA spikes to mucoproteins on the surface of cells. After binding, the virus enters into the cell by endocytosis via coated pits into endocytotic vesicles as endosomes. Uncoating takes place after acidification of the endosomes. During the initial phase of infection (approximately 2h), active host cell DNA synthesis is required. Inside the nucleus the viral RNA uses the methylated cap of host cell mRNA as primers for RNA synthesis (cap snatching). Two classes of (+) sense RNA are made inside the nucleus of infected cells.
• Incomplete, 3' polyadenylated transcripts which are exported to the cytoplasm and serve as mRNAs.
• cRNA - complete, (+) sense copies of the (-) sense viral, which serve as template for the synthesis of progeny (-) sense vRNAs.
• Most of the proteins made (e.g. HA, NA) remain in the cytoplasm or become associated with the cell membrane. However, the NP protein migrates back into the nucleus, where it associates with newly-synthesized vRNA to form new nucleocapsids. These migrate back out into the cytoplasm and towards the cell membrane. The exact packaging mechanism by which eight distinct genome segments are packed into each progeny virion particle is not known.