When this happens, the altered virus preferentially reactivates previously activated high-affinity memory B cells and spur antibody production.

The virus infects the salivary glands, establishes latency, and periodically reactivates to spread infection to other hosts.

Periodically, the virus can reactivate, during which time the patient is again infectious, but usually without any symptoms of illness.

Periodically, the virus can reactivate and is commonly found in the saliva of infected persons.

As the virus reactivates in these nerves, it can interfere with their normal functioning.

But decades later, as immunity wanes, the virus can reactivate to cause shingles, a painful condition, or herpes zoster.

Scientists are not certain why the virus reactivates, or why it only reactivates in about 20% of the people who have had chickenpox.

When the virus that causes chickenpox reactivates, it causes shingles.

Infected animals will be continuous shedders throughout their lifetime when the virus reactivates; therefore, successfully propagating the disease.

In approximately one-third of people, the virus can "wake up" or reactivate to cause disease.