Which of the following is false regarding antigenic drift?
|A||It occurs every 10- 12 years|
|B||It occurs under pressure from immunity|
|C||It occurs only in influenza A|
|D||It is responsible for epidemics of influenza"|
a. The influenza-A virus is unique among the viruses because it is frequently subject to antigenic variation, both major and minor. When there is a sudden, complete or major change, it is called a shift; and when the antigenic change is gradual over a period of time, it is called a drift.
b. Antigenic shift results from genetic recombination of human with animal or avian virus, providing a major antigenic change.
c. This can cause a major epidemic or pandemic involving all age groups.
d. Antigenic drift involves 'point-mutation' in the gene due to selection pressure by immunity in the host population.
e. Antigenic changes occur to a lesser degree in group-B influenza viruses; and influenza-C virus appears to be antigenically stable. Since its isolation in 1933, the major antigenic changes have occurred twice in influenza-A virus; once in 1957 and again in 1968.