Which of the following best explains why some viruses appear to disappear and then re-emerge in the host at a later time?

• A. They mutate rapidly, making them undetectable until a new strain emerges.
• B. They can enter a latent phase, remaining dormant within host cells before reactivating.
• C. They are completely eliminated by the immune system and then re-infect from external sources.
• D. They hide in the bloodstream and circulate until conditions are favorable for replication.

Answer: (B)

Verified step by step guidance

1. Understand the concept of viral latency: Some viruses have the ability to enter a dormant state within host cells, where they do not actively replicate or cause symptoms. This is known as the latent phase.
2. Recognize that during latency, the virus is not eliminated but remains hidden inside certain cells, evading the immune system and antiviral treatments.
3. Identify that the virus can later reactivate from this latent state, beginning to replicate again and causing symptoms to reappear in the host.
4. Compare this mechanism to other options such as rapid mutation or external re-infection, noting that latency specifically explains the disappearance and later re-emergence without new infection.
5. Conclude that the best explanation for viruses disappearing and re-emerging is their ability to enter a latent phase, remaining dormant before reactivating.