RNA viruses change frequently because they:
a. Lack proofreading ability during replication
b. Frequently acquire new virulence factors from other species
c. Excise host genetic material when they exit latent periods
d. Incorporate host genetic material with the viral genetic material
e. All of these
The correct answer and explanation is:
The correct answer is a. Lack proofreading ability during replication.
RNA viruses are known for their high mutation rates, and this is primarily due to the lack of proofreading ability during replication. RNA viruses replicate their genomes using an RNA-dependent RNA polymerase (RdRp), which is not equipped with a proofreading mechanism like the DNA polymerases in cells. As a result, mistakes or errors that occur during the replication process are not corrected, leading to mutations. These mutations can accumulate rapidly, causing the virus to evolve quickly.
This lack of proofreading contributes significantly to the variability of RNA viruses. While DNA viruses typically replicate with fewer errors because of the proofreading ability of DNA polymerases, RNA viruses experience a higher mutation rate, which allows them to adapt to changing environments, evade the immune system, and develop resistance to antiviral drugs more efficiently.
Additionally, the high mutation rates in RNA viruses lead to the generation of viral quasispecies, which are populations of closely related viral variants. These variants can have different characteristics, including varying abilities to infect host cells or evade immune responses, further contributing to the virus’s ability to rapidly adapt.
While other options may seem plausible, they do not fully explain why RNA viruses change frequently. Option b is not entirely accurate, as RNA viruses do not necessarily acquire new virulence factors from other species frequently. Option c is more relevant to latent viruses, which is a different phenomenon. Option d involves horizontal gene transfer, which can happen in some viruses but is not the primary reason for the high mutation rates in RNA viruses.
Thus, the high mutation rate due to the lack of proofreading ability during replication is the main reason RNA viruses change frequently.