How does coinfection of a single cell by multiple strains of a virus increase its pathogenicity?

• A. It enhances cellular replication
• B. Coinfection provides the opportunity for an antigenic shift
• C. It decreases the immune response
• D. It allows for horizontal gene transfer

Answer: (B)

The increase in pathogenicity through coinfection of a single cell by multiple strains of a virus primarily occurs due to the opportunity for an antigenic shift. When different strains of a virus infect the same host cell, their genetic material can reassort or recombine during replication. This genetic mixing can lead to the emergence of new viral strains with different characteristics compared to the parental strains.

Antigenic shift is particularly significant because it can alter surface proteins found on the virus, allowing it to evade the host's immune response. This means that even if the host has immunity to one strain, the new strain resulting from the reassortment may not be recognized by the immune system, increasing the likelihood of serious infections or outbreaks. This mechanism is notably observed in influenza viruses, leading to new strains that can cause pandemics.

While the other choices present concepts related to viral behavior, they do not capture the critical impact of genetic reassortment on pathogenicity in the way that antigenic shift does. Thus, coinfection predominantly enhances the capacity for a virus to adapt and evade host defenses, making the pathogen more dangerous.