Infection

Concepts on Infection

What is Infection?

• Invasion of an Organism's Body
• by disease-casing agents
  • viruses
  • viroids
  • prions
  • bacteria
  • nematodes: roundworms and pin worms
  • arthropods: ticks, mites, fleas, lice
  • Fungi: 'ringworm'
  • Macroparasites: Tape worms and helminths
• Multiplication of agents
• Host tissues
  • Reacts to
    • Organisms
    • Toxins they produce
  • Reactions
    • Innate Immune Response: e.g. Inflammation
    • Adaptive Response

Classification of Infections

• Apparent Vs Inapparent Vs Latent
  • Apparent Infections: Symptomatic Symptoms (Sepsis)
  • Inapparent/ Silent/ Subclinical/ Occult Infections: infection that is active but does not produce noticeable symptoms
  • Latent Infection: inactive or dormant infection. e.g. latent tuberculosis, Herpesviridae
• Acute Vs Chronic
  • Acute Infection
  • Chronic Infection
• Infection by Causative agent: Bacterial, Viral, Fungal, Parasitic)
• Primary Vs Opportunistic
  • Primary Pathogens: Cause disease within normal healthy hosts. Intrinsic virulence is a consequence of their need to reproduce and spread.
  • Opportunistic Pathogens: Cause disease in a host with depressed resistance
    • In contact with host: Pathogenic bacteria, fungi in GUT or respiratory track
    • Innocuous microbes from other Hosts: e.g. clostridium difficile colitis
    • From the environment due to traumatic introduction: e.g. wounds
    • impairment of host defenses due to
      • Genetic defects e.g. Chronic granulomatous disease
      • Exposure to antimicrobial drugs or immunosuppresive chemicals: e.g. poisoning or cancer chemotherapy
      • Exposure to ionizing radiation
      • Exposure to infectious disease with immunosuppressive activity e.g. measles, malaria, HIV disease
• If it is an Infectious Desease: Transmissible disease or communicable disease
  • Tools for testing if a disease is infectious
    • Koch's postulates: infectious agent be identified only in patnents and not in healthy controls. and patients who contract the agent also develop the disease
    • Epidemiology
  • Infectious/ Transmissible/ Communicable Level of Disease Outbreak
    • Sporadic
    • Endemic
    • Epidemic
    • Pandemic
  • Mode of Transmission
    • Droplet contact/ respiratory route/
      • Resulting in airborne disease.
      • If an infected person coughs or sneezes on another person the microorganisms, suspended in warm, moist droplets, may enter the body through the nose, mouth or eye surfaces.
    • Fecal-oral transmission
      • foodstuffs or water become contaminated (by people not washing their hands before preparing food, or untreated sewage being released into a drinking water supply) and the people who eat and drink them become infected.
      • Common fecal-oral transmitted pathogens include Vibrio cholerae, Giardia species, rotaviruses, Entameba histolytica, Escherichia coli, and tape worms.
      • Most of these pathogens cause gastroenteritis.
    • Sexual transmission:
      • resulting disease being called sexually transmitted disease
    • Oral transmission
      • may be caught through direct oral contact such as kissing, or by indirect contact such as by sharing a drinking glass or a cigarette.
    • Contact Transmission/ By direct contact
      • e.g. athlete's foot, impetigo and warts
    • Vertical transmission
      • directly from the mother to an embryo, fetus or baby during pregnancy or childbirth
      • May occur when the mother gets an infection as an intercurrent disease in pregnancy.
    • Latrogenic transmission
      • due to medical procedures such as injection or transplantation of infected material.
    • Vector-borne transmission
      • transmitted by a vector, which is an organism that does not cause disease itself but that transmits infection by conveying pathogens from one host to another
      • Culex mosquitos (Culex quinquefasciatus shown) are biological vectors that transmit West Nile Virus.
  • Contagious Disease
    • An infectious disease that is especially infective or easily transmitted
    • transmitted by contact with an ill person or their secretions
• By Anatomic Location
  • Urinary tract infection
  • Skin infection
  • Respiratory tract infection
  • Odontogenic infection (an infection that originates within a tooth or in the closely surrounding tissues)
  • Vaginal infections
  • Intra-amniotic infection
  • Location Specific Inflammation - pneumonia, meningitis and salpingitis.

How do I know if I have an Infectious Disease?

• By Medical Diagnostics
  • Symptomatic Diagnostics
  • Microbial Culture
  • Microscopy
  • Biochemical tests
  • Molecular Diagnostics
  • Indication of Tests

Medications used to treat infections

• Antibiotics
• Antivirals
• Antifungals
• Antiprotozoals
• Antihelminthics

Reference

• Personal Biology notes from NUS
• https://en.wikipedia.org/wiki/Infection