What is antigenic shift and drift in influenza virus. What are the implications.
What are the risk factors for complications following influenza infection
Q58 marksShort Essays
Answer
Antigenic shift and antigenic drift in influenza virus
Antigenic drift: minor, gradual changes in the influenza virus surface glycoproteins (haemagglutinin and neuraminidase) arising from the accumulation of point mutations during viral replication (due to the error-prone nature of the viral RNA-dependent RNA polymerase, which lacks proofreading capability). Occurs continuously in both influenza A and B viruses. Implication: results in the emergence of new antigenic variants each season, sufficient to partially evade pre-existing population immunity — this is the reason seasonal influenza epidemics occur, and why the influenza vaccine composition must be reviewed and updated annually.
Antigenic shift: a major, abrupt change in the haemagglutinin and/or neuraminidase surface antigens, arising from reassortment of gene segments between two different influenza A viral strains (e.g., a human and an animal/avian strain) co-infecting the same host cell — possible because the influenza genome is segmented. Occurs only in influenza A (which alone has multiple subtypes circulating in both humans and animal reservoirs, providing the substrate for reassortment). Implication: produces a novel viral subtype to which the population has little or no pre-existing immunity, creating the potential for pandemic spread (as occurred with the 1918, 1957, 1968, and 2009 influenza pandemics).
Risk factors for complications following influenza infection:
Extremes of age — young children (particularly under 2 years) and elderly individuals (typically over 65 years).
