The best evidence that viruses require a host to replicate can be observed
a) by the eclipse phase.
b) by CPE.
c) by using a diagnostic technique.
d) by plaque assay in presence and absence of host cells.
e) by infection and the spread of disease.
The correct answer and explanation is:
The correct answer is a) by the eclipse phase.
The eclipse phase refers to the period during viral replication when the virus has entered the host cell and is actively replicating its genetic material and producing viral proteins, but no new viral particles are yet detectable. This phase occurs after the virus attaches to the host cell and injects its genetic material, and before new viral particles are assembled and released. The eclipse phase is critical because it demonstrates that viruses are entirely dependent on a host cell’s machinery to replicate. During this phase, the virus is effectively “invisible” in terms of observable effects, as no new virions (virus particles) are produced yet. The fact that viruses cannot replicate outside of a host and undergo this phase underscores the necessity of a living host for viral reproduction.
Here’s a breakdown of the other options:
- b) CPE (cytopathic effect) refers to visible changes or damage in a host cell caused by the virus, but this is a consequence of viral replication rather than direct evidence of the virus’s reliance on a host to replicate.
- c) Diagnostic techniques like PCR or serology can detect the presence of a virus or its antibodies, but they don’t directly demonstrate the requirement for a host during replication.
- d) Plaque assay involves infecting a layer of host cells with a virus and counting the plaques (areas of cell death) that form. While this is a useful method to measure viral replication, it assumes the presence of host cells and doesn’t directly show the virus’s need for a host to replicate.
- e) Infection and the spread of disease provide evidence of the virus’s ability to infect and spread, but again, it does not directly demonstrate that viruses require host cells for replication.
In summary, the eclipse phase most clearly demonstrates that viruses need a host to replicate because it reflects the internal, host-dependent replication process that occurs before the formation of new virions.