NEET 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: -Many viruses are capable of establishing persistent infections, of which two types are recognized: chronic and latent.

Detailed explanation-5: -Periods of Disease. The five periods of disease (sometimes referred to as stages or phases) include the incubation, prodromal, illness, decline, and convalescence periods (Figure 16.3). The incubation period occurs in an acute disease after the initial entry of the pathogen into the host (patient).