Infection and its various types

Introduction to infection

  • An infection is the detrimental colonization of a host organism by a foreign species.
  • In an infection, the infecting organism seeks to utilize the host’s resources to multiply, usually at the expense of the host.
  • The infecting organism, or pathogen, interferes with the normal functioning of the host and can lead to chronic wounds, gangrene, loss of an infected limb, and even death.
  • The host’s response to infection is inflammation.
  • A pathogen is usually considered a microscopic organism though the definition is broader, including parasites, fungi, viruses, prions, and viroids.
  • A symbiosis between parasite and host, whereby the relationship is beneficial to the former but detrimental to the latter, is characterized by
  • The branch of medicine that focuses on infections and pathogens is infectious disease.
  • There are various types of infections. Some of them are as follows:

Types of Infection

  1. In-apparent (sub-clinical infection)
  • Infection that causes no clinically apparent symptoms is in-apparent infection.
  • The disease agent may multiply within the host but does not show signs and symptoms.
  • Sub-clinical infections can be detected only by laboratory tests.
  • e.g., in some diseases like rubella, mumps, polio, hepatitis A and B, a great deal of sub-clinical infection occurs.
  1. Latent infection
  • In latent infection, the host does not shed the infectious agent which lies dormant within the host without symptoms.
  • Latent infection occurs in herpes simplex infection.

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  1. Acute infection
  • Acute infections are those that come on rapidly, are accompanied by severe symptoms, and progress to climax.
  • An example of acute infection is measles and streptococcal pharyngitis.
  • These types of infections also heal rapidly.
  1. Chronic infection
  • Chronic infections occur slowly, generally are accompanied by mild to severe symptoms.
  • They persist over a long period of time, with an extended convalescence. E.g., tuberculosis, etc.
  1. Localized infection
  • A localized infection remains at a specific body site, usually the first site of infection.
  • e.g., UTI caused by Escherichia coli.
  1. Systemic infection
  • It is the one that spread to alternative sites in the body such as deeper organs or tissues.
  • e.g., enteric fever caused by Salmonella typhi.

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  1. Primary infection
  • It is established in a previously healthy body.
  • It is an initial localized infection that decreases host resistance and provides the way for further invasion by the same microorganisms or other microorganisms.
  • e.g., viral influenza.
  1. Secondary infection
  • It develops in the body after it has already been infected by different microorganisms.
  • It occurs after primary infection because the host resistance power is diminished by the primary infection.
  • e.g., Pneumococcal pneumonia following viral influenza.




Infection and its various types