IV. VIRUSES

K. GENERAL CATEGORIES OF VIRAL INFECTIONS

Fundamental Statements for this Learning Object:

1. Acute infections are of relatively short duration with rapid recovery.
2. Persistent infections are where the viruses are continually present in the body.
3. 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.
4. In a chronic virus infection, the virus can be demonstrated in the body at all times and the disease may be present or absent for an extended period of time.
5. Slow infections are ones in which the infectious agents gradually increase in number over a very long period of time during which no significant symptoms are seen.

 

LEARNING OBJECTIVES FOR THIS SECTION

Viruses are infectious agents with both living and nonliving characteristics.

1. Living characteristics of viruses

a. They reproduce at a fantastic rate, but only in living host cells.

b. They can mutate.

2. Nonliving characteristics of viruses

a. They are acellular, that is, they contain no cytoplasm or cellular organelles.

b. They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery. In other words, viruses don't grow and divide. Instead, new viral components are synthesized and assembled within the infected host cell.

c. The vast majority of viruses possess either DNA or RNA but not both.

General Categories of Viral Infections of Humans

Most viruses that infect humans, such as those that cause routine respiratory infections (e.g., cold viruses, influenza viruses) and gastrointestinal infections (e.g., Rotaviruses, Noroviruses), cause acute infections. Acute (def) infections are of relatively short duration with rapid recovery.

In persistent infections, the viruses are continually present in the body. Some persistent infections are late complications following an acute infection and include subacute sclerosing panencephalitis (SSPE) that can follow an acute measles infection and progressive encephalitis that can follow rubella. Other persistent infections are known as latent (def) viral infection. 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. Examples include infections caused by HSV-1 (fever blisters), HSV-2 (genital herpes), and VZV (chickenpox-shingles). In the case of chronic virus infections, the virus can be demonstrated in the body at all times and the disease may be present or absent for an extended period of time. Examples include hepatitis B (caused by HBV) and hepatitis C (caused by HCV). Slow infections are ones in which the infectious agents gradually increase in number over a very long period of time during which no significant symptoms are seen. Examples include AIDS (caused by HIV-1 and HIV-2) and certain lentiviruses that cause tumors in animals. Although not viruses, prions also cause slow infections.

Medscape article on infections associated with organisms mentioned in this Learning Object. Registration to access this website is free. Adenoviruses Herpes Simplex Varicella-Zoster Virus Cytomegalovirus Hepatitis B Enteroviruses Rhinoviruses Rubella Hepatitis C Measles Influenza HIV Infection and AIDS

 

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