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Foundations in Microbiology, 4/e
Kathleen Park Talaro, Pasadena City College
Arthur Talaro

Microbe-Human Interactions: Infection and Disease

Chapter Overview

  • Humans are constantly exposed to microbes in their environment, mostly without harm.
  • When microbes colonize the human body, sometimes they become part of the normal flora and other times, they may cause infection and disease.
  • Normal flora are bacteria, fungi, and protozoa that reside naturally in the skin, gastrointestinal tract, mucous membranes, and genitourinary tracts, where they provide a stabilizing balance.
  • Pathogens invade the body and cause harm to the tissues by means of virulence factors.
  • An infection occurs when an adequate dose of pathogens gains access to the body through a certain route, and subsequently adheres, grows, and disrupts tissues.
  • Pathogens produce virulence factors such as toxins and enzymes to help them invade the host and damage cells.
  • Types of infections include local, systemic, blood, latent, primary, secondary, acute, chronic, and asymptomatic.
  • Infections and diseases often follow predictable patterns involving an incubation period, invasion period, and convalescent period.
  • The effects of infections and diseases are manifest as symptoms and signs, which may lead to long-term, permanent damage.
  • Epidemiology is a field that studies the patterns of disease occurrence in a population.
  • Epidemiologists are concerned with monitoring the numbers of cases; the geographic distribution; the sex, age, and ethnicity of affected people; and the mortality rate.
  • Disease statistics are reported to various public health agencies to keep track of regional, sporadic, epidemic, and worldwide levels of distribution.
  • Pathogens originate from humans, animals, food, water, and the environment. Some are transmissible and some are not.
  • Transmissible infectious diseases may be spread by direct or indirect means by overtly infected people, carriers, vectors, and vehicles.
  • A significant number of infections are acquired through exposure to the hospital environment.
  • The causative agents for diseases are determined by a standard set of scientific trials developed by Koch.