AP BIOLOGY

Detailed explanation-1: -Definition. Persistent infections are characterized as those in which the virus is not cleared but remains in specific cells of infected individuals. Persistent infections may involve stages of both silent and productive infection without rapidly killing or even producing excessive damage of the host cells.

Detailed explanation-2: -Persistent infections are where the viruses are continually present in the body. In a latent viral infection the virus remains in equilibrium with the host for long periods of time before symptoms again appear, but the actual viruses cannot be detected until reactivation of the disease occurs.

Detailed explanation-3: -In contrast to acute viral infections, persistent infections last for long periods, and occur when the primary infection is not cleared by the adaptive immune response. Varicella-zoster virus, measles virus, HIV-1, and human cytomegalovirus are examples of viruses that cause typical persistent infections.

Detailed explanation-4: -One well-known example of a chronic infection in humans is HIV, in which the infection cannot be cleared by the immune system and the virus continues to replicate. AIDS results when the immune system is finally overwhelmed by the virus.

Detailed explanation-5: -The periods of disease include the incubation period, the prodromal period, the period of illness, the period of decline, and the period of convalescence. These periods are marked by changes in the number of infectious agents and the severity of signs and symptoms.