How does acyclovir inhibit herpes virus
replication?
A. They block capping of viral mRNA
B. They inhibit reverse transcriptase activity
C. They inhibit viral polymerase activity
D. They block viral uncoating
Ans. C.
Acyclovir and
ganciclovir are variants of
acycloguanosine and are used to treat herpes simplex virus and
cytomegalovirus infections, respectively. Both agents are viricidal and act by
interfering with viral polymerase activity. In the case of herpes simplex virus
infection, the virally-coded thymidine kinase monophosphorylates the acyclovir.
Cellular kinases then add two more phosphates, creating a nucleotide that is
accepted by the virally-coded DNA polymerase. The structural analog is
incorporated into the growing DNA chain and elongation is terminated.
Ribavirin, used to treat paramyxovirus (respiratory syncytial virus) infection,
works by interferring with viral messenger RNA (mRNA) capping. Amantadine, used
to treat influenza A infections, blocks viral un coating. It is most effective
when given before viral infection occurs. Reverse transcriptase inhibitors
(e.g., azidothymidine, didioxycytocine, didioxyinosine) directly interfere with
normal enzyme activity. These agents are virostatic, and virus growth occurs
when the agents are removed. Interferons are induced as a result of viral
infection of a cell. Products of viral nucleic acid replication activate genes
that code for interferons, which directly prevent virus growth by inducing an
antiviral protein within virus- infected cells.
