MICRO

• Disease


  Result of an undesirable relationship between the host and the pathogen, marked by interruption in the normal functioning of a body part or parts
• Infection


  Invasion of the body by pathogenic microorganisms. The term is not synonymous with disease
• Symbiosis


  Prolonged and close interaction between organisms of different species
• Mutualism


  A form of symbiosis in which both organisms benefit from the relationship
• Commensalism


  A form of symbiosis in which one organism benefits from another organism without causing harm to it
• Parasitism


  A form of symbiosis where one organism benefits from another organism and at the same time causes harm to the other
• Pathogenicity


  Ability of an organism to produce disease. An organism that can produce disease in humans is said to be pathogenic
• Virulence


  Describes the degree of pathogenicity of an organism or the degree to which an organism can produce disease
• Contamination


  Presence of unwanted materials (chemical, biological, or radiological) where they should not be or at concentrations above the normal. The presence of these substances may not necessarily lead to harm
• Pollution


  Presence of contaminants that can cause adverse biological effects to humans and communities. All pollutants are contaminants but not all contaminants are pollutants
• Bacteremia


  Presence of bacteria in the blood
• Septicemia


  Presence of actively multiplying bacteria in the blood, usually from a source of infection. The condition is called sepsis
• Pyemia


  Presence of pus-producing bacteria in the bloodstream
• Viremia


  Presence of viruses in the blood
• Toxemia


  Presence of toxins in the blood
• Chain of infection


  1. Pathogenic organism leaves its host or a reservoir through a portal of exit

  2. A susceptible organism acquires the infection through a given mode of transmission, entering the body of the susceptible host through a portal of entry

  3. Organism starts to multiply and produce disease
• Reservoirs


  • Animals
  • Humans
  • Environment
• Zoonotic infections


  Infectious diseases that can be transmitted from an animal to humans
• Carriers


  Infected humans who may harbor the organism but only develop sub-clinical disease
• Types of carriers


  • Asymptomatic or healthy carriers
  • Incubatory carriers
  • Chronic carriers
  • Convalescent carriers
• Environmental reservoirs


  • Water
  • Soil
  • Plants
• Portal of exit


  Route by which an infectious agent exits its host
• Modes of transmission


  • Direct contact
  • Indirect contact
• Direct contact - Person-to-person


  Transmission through skin-to-skin contact, kissing, or sexual transmission
• Direct contact - Droplet spread


  Transmission of respiratory pathogens during coughing and sneezing
• Indirect contact - Airborne transmission


  Transmission of infectious agents through dust or aerosols
• Indirect contact - Vehicle transmission


  Transmission of organisms through media such as food, water, milk, or biologic substances such as blood and body secretions
• Indirect contact - Vector transmission


  Transmission by insects that can transmit an infectious agent, either through mechanical or biological means
• Portal of entry


  How the infectious agent enters a susceptible host
• Host


  The final link in the chain of infection. Susceptibility is affected by constitutional/genetic factors and immune status
• Schistosoma haematobium


  Blood fluke that leaves the body of the host through urine
• Hepatitis B virus and HIV


  Enter the susceptible host through blood and blood products
• Host


  The final link in the chain of infection, whose susceptibility is affected by constitutional/genetic factors and immune status
• Patients born with the gene that codes for the sickle cell trait are less prone to develop malaria than those who were not born with the trait
• Immune system


  Natural barriers that prevent entry of potential pathogenic organisms, and a highly functional system that can mount adequate defenses to fight and destroy any invading pathogen
• Factors that may impact the human immune system include poor nutritional status, chronic intake of alcoholic beverages, or any condition that dampens the immune response
• Communicable disease


  A disease that is spread from one host to another, either directly or indirectly
• Communicable diseases

  • Measles, tuberculosis, typhoid fever
• Contagious disease


  A communicable disease that is easily and rapidly spread from one person to another
• Contagious diseases

  • Measles, chickenpox