Important Terms

Question 1

• Antigenic shift

Answer 1

1. process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains.
2. applied specifically to influenza-other viruses (visna virus in sheep)
3. occurs only in influenza A because it infects more than just humans.

Question 2

Antigenic drift

Answer 2

1. occurs in all types of influenza including influenza A, influenza B and influenza C
2. refers to the accumulation of genetic mutations that cause an alteration in the surface of the virus (the mutated antigen ‘drifts’ from the original conformation). This is one of the main reasons why a novel flu vaccine is required every year.