Which type of infection persists for a long period of time sometimes for life?

Learning Objectives

1. Describe and give an example of an acute viral infection, a late complication following an acute infection, a latent viral infection, a chronic viral infection, and a slow viral infection.

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 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 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

Summary

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.

This page titled 10.11: General Categories of Viral Infections is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Gary Kaiser via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

There is no single mechanism responsible for establishing a persistent infection; a key feature is reduction in host defenses and the ability of the virus to kill cells. Many arenaviruses, such as lymphocytic choriomeningitis virus, do not kill cells and will cause a persistent infection if the host cannot clear the virus. In some persistent viral infections there are alternate cycles of virion production and quiescence. An example is Epstein-Barr virus, the agent of infectious mononucleosis. After the initial bout of fever, sore throat, and swollen lymph glands, the virus establishes a dormant infection in which the viral genome persists in cells of the immune system. Periodically the infection is reactivated and infectious virions are shed in the absence of clinical symptoms. These reactivations lead to transmission of the infection to new hosts.

Bovine viral diarrhea virus infection is another example of how persistence is regulated by the interplay of the host immune response and viral cell killing. This virus establishes a lifelong persistent infection in most of the world’s cattle. The infected animals produce no detectable anti-viral antibody or T-cells. The virus is passed from the mother to fetus early in gestation. Infection does not stimulate the production of interferon (IFN), and therefore the adaptive immune system is not activated. Because infection does not kill cells, a persistent infection ensues.

Many infections persist because viral replication interferes with the function of cytotoxic T-lymphocytes (CTLs), immune cells that are extremely important for clearing viral infections. Infected cells are recognized when CTLs detect viral antigens on the cell surface. This recognition process requires presentation of the viral peptides by major histocompatibilty complex (MHC) class I proteins. Many viral proteins interfere with different steps of the MHC class I pathway, including the synthesis, processing, and trafficking of the protein. Even transport to the cell surface of viral peptides – produced from viral proteins by the large protein complex known as the proteasome – may be blocked.

An amazing example of such immune modulation occurs in cells infected with cytomegalovirus (CMV). This betaherpesvirus causes a common childhood infection of little consequence in healthy individuals. The infection is never cleared, and the virus persistently infects salivary and mammary glands and the kidney. When latently infected individuals are immunosuppressed by drugs or HIV infection, viral replication ensues with life-threatening consequences. CMV persists in the host because the viral genome encodes multiple proteins that interfere with MHC class I presentation of viral antigens. One viral protein blocks translocation of peptides into the lumen of the endoplasmic reticulum, while two other viral proteins cause degradation of MHC class I proteins before they reach the cell surface.

There are many more examples of how virus infections modulate the immune response, leading to persistent infection. Not surprisingly, many of the processing or regulatory steps that are targets of viral modulation were not even known until it was discovered that they were blocked by virus infection.

What infections can last for years?

What are the four types of persistent infection?