IV. VIRUSES
K. TYPES OF VIRAL INFECTIONS
The overall purpose of this Learning Object is to learn some of the common terms used to describe the various types of viral infections in humans.
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.
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.
Student-Authored Descriptions of Viral Infections
Astroviruses by Michele Stedding
Coxsackievirus by Mandy Hughes
Coxsackievirus by Salyna Riggs
Cytomegalovirus (CMV) by Cindi Chou
Ebola by Christine Sprinkle
Ebola by Dianne Bettick
Ebola by LaTanya Gary
Epstein-Barr Virus (EBV) by Erica Rome
Hantavirus by Jennifer Robinson
Hepatitis A (HAV) by Anastasiya Lyudkevich
Hepatitis B (HBV) by Karen Neff
Hepatitis C (HCV) by Rosemary Bewley
Hepatitis C (HCV) by Corinne Borel
Herpes Simplex types 1 and 2 (HSV1 &HSV2) by Katrina Armstrong
Herpes Simplex types 1 and 2 (HSV1 & HSV2) by Cindy Dubs
Herpes Simplex type 2 ( HSV2) by Lauren Bentley
Human Immunodeficiency Virus (HIV) by Steven Merrill
Human Papilloma Viruses (HPV) by Megan Johnson
Human Papilloma Virus (HPV) by Laura Moy
Influenza by Kenneth Agboifo
Measles (Rubeola) by Peggy Engel
Measles (Rubeola) by Sumara Choudhry
Measles (Rubeola) by Yashu Karki
Mumps by Trudy Ann Hinds
Noroviruses by Kristina Garner
Poliomyelitis by Deborah Malin
Rabies by Pamela Russillo
Rabies by Lauren Mekalian
Rhinoviruses (colds) by Nina Mezu
Rift Valley Fever by LaWanda Morgan
Respiratory Syncytial Virus (RSV) by Ben Kaufman
Respiratory Syncytial Virus (RSV) by Christen Strickler
Rotaviruses by Chrissy Blake
Rotaviruses by Shana Lucas
Varicella (chickenpox) by Rosemary Brunet
Varicella (chickenpox) by Violeta Genova
Viral Meningitis by Denise Grandea
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Updated: July, 2007
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