Point mutations in the hemagglutination (HA) or neuraminidase (NA) genes during viral ribonucleoprotein (RNP) replication give rise to new strains. This mechanism is known as the antigenic:

a. drift.
b. shift.
c. re-assortment.
d. modification.


A
The antigenic drift is caused by sequential point mutations in the HA or NA genes that occur during viral RNP replication and immune selection, which give rise to new strains; thus, the an-tigenic drift gives the virus the ability to re-infect nonimmune susceptible hosts each season. Another phenomenon is the antigenic shift. Influenza A solely possesses this mechanism; it in-volves the complete re-assortment of the segmented viral genome during a co-infection with a nonhuman animal, which results in major antigenic change and periodic worldwide outbreaks (pandemics) of a never-before-circulated type of influenza A virus. Influenza B undergoes anti-genic change very slowly.

Biology & Microbiology

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