Influenza Virus: Has receptors allowing binding to host cell surfaces.
Antibodies: Bind to viral receptors to prevent the virus from infecting cells.
Neutralizing Antibodies: Block the virus's ability to infect host cells.
Viral Evasion Mechanisms
Escape from Neutralizing Antibodies:
Occurs when viruses mutate or combine genetic material, evading immune responses.
Example: Two strains of influenza virus infect the same cell.
Antigenic Shift
Definition: Large changes in the virus's antigenicity, often leading to immune evasion.
Mechanism:
Progeny viruses from doubly infected cells may mix genome segments from both parental strains.
New virus may carry receptor segments from a different strain.
Result: Neutralizing antibodies against the original virus may not recognize the new receptor.
Implications
Immune Ineffectiveness: Previous immunity may become ineffective against new viral strains.
Epidemics:
Antigenic shift is associated with large-scale epidemics due to widespread immune evasion.
Summary
Viral evolution through antigenic shift can significantly impact public health by enabling viruses to escape immune defenses, leading to potential outbreaks and necessitating continuous monitoring and vaccine updates.