Microbiology and Parasitology

• Epidemiology


  The study of disease and its distribution in populations, and the application of this study to control health problems
• Epidemiologists


  • Study the factors that determine the frequency, distribution, and determinants of diseases in human populations
• What do Epidemiologists do?

  • Research
  • Surveillance
  • Investigation
  • Monitoring
  • Reporting
• Characteristics of interest to Epidemiologists


  • Characteristics of various pathogens
  • Susceptibility of different human populations (due to overcrowding, lack of immunization, insufficient nutritional status, inadequate sanitation procedures, and other factors)
  • Locations where pathogens are
  • Various ways in which infectious diseases are transmitted
• What do Epidemiologists study?

  • Who becomes infected?
  • What pathogens are causing the infections?
  • Where do the pathogens come from?
  • When do certain diseases occur?
  • Why do some diseases occur in certain places but not in others?
  • How are pathogens transmitted and treated?
• Zoonotic Disease


  Disorders that humans acquire from animal sources
• Infectious Disease


  Disorders caused by organisms such as bacteria, viruses, fungi or parasites
• Communicable Disease


  Illnesses caused by viruses or bacteria that people spread to one another through contact with contaminated surfaces, bodily fluids, blood products, insect bites, or through the air
• Contagious Disease


  A communicable disease that can spread rapidly from person to person through direct contact, indirect contact, or droplet contact
• Incidence


  The number of new cases of a disease in a defined population during a specific period
• Prevalence


  The proportion of a population who have a specific disease characteristic in each period
• Point prevalence


  The proportion of a population that has the characteristic at a specific point in time
• Period prevalence


  The proportion of a population that has the characteristic at any point during a given period of interest
• Morbidity Rate


  The number of new cases of a particular disease that occurred during a specified period per a specifically defined population (usually per 1,000, 10,000 or 100,000 population)
• Mortality Rate


  The ratio of the number of people who died of a particular disease during a specified period per a specified population; also referred to as death rate
• Chain of Infection


  • Infectious Agent (Bacteria, Virus, Fungi, Parasite)
  • Reservoir (Living: Human Body, Animals; Non-Living: Environment, Fomites)
  • Portal of Exit/Entry
  • Mode of Transmission
  • Susceptible Host
• Pathogenicity


  Ability of an organism to cause disease
• Virulence


  Ability to cause damage to a host
• Infectious Dose


  The amount of a pathogen that is required to establish an infection
• Toxigenicity


  Ability of a pathogenic organism to produce injurious substances that damage the host
• Microbial Adaptability


  Gradual modifications of microorganisms in a stressful environment to enhance their tolerance
• Types of Human Carriers

  • Passive Carriers (colonized with a pathogen but not causing disease)
  • Incubatory Carriers (can transmit the agent during the incubation period before clinical illness begins)
  • Convalescent Carriers (have recovered from illness but remain capable of transmitting to others)
• Zoonosis


  An infectious disease that is transmitted between species from animals to humans (or from humans to animals)
• Ways zoonoses may be acquired

  • Direct contact with an animal
  • Inhalation or ingestion of the pathogen
  • Injection of the pathogen by an arthropod
• Factors pertaining to the environment

  • Physical factors such as climate, season
  • Geographic location
  • Availability of appropriate reservoirs
  • Sanitary and housing conditions
  • Availability of potable water
• Fomites


  Objects or materials which are likely to carry infection
• Portals of Exit/Entry


  • Respiratory Tract
  • GI/GU Tract
  • Body Fluids (Except for Sweat) such as Blood, Urine, Semen
  • Skin, Mucous Membrane
  • Transplacental
• Modes of Transmission


  • Horizontal transmission
  • Vertical transmission (from mother to offspring)
  • Direct contact (Kissing, Sex, Contact with body fluids, Touching)
  • Droplet Transmission (Cough, Sneezing)
  • Airborne Transmission (Carried by dust or droplet nuclei)
  • Vehicle-borne Transmission (Soiled clothes, Surgical instruments)
  • Vector-borne Transmission (Mites, Ticks, Flies, Mosquitoes)
• Susceptible Host


  Any person who is not vaccinated or otherwise immunized, or a person with a weakened immune system who has a way for the germs to enter the body
• Factors affecting susceptibility


  • Health status (hospitalization, underlying disease, immunization history, medications history)
  • Nutritional Status
  • Hygiene
  • Age
  • Travel
  • Lifestyle
• Proper collection and transport of specimens

  • Important to maximize the outcome of laboratory tests for the diagnosis of infectious diseases
• Principles of specimen collection

  1. Specimens should be collected during the acute phase of infection and before the initiation of antibiotic therapy, if possible

  2. Obtain an adequate amount of the specimen necessary for all tests

  3. Avoid potential contamination of the specimen by using proper collection technique

  4. Check local laboratory guidelines for the specimen collection recommendations for each test
• Principles of specimen labelling and transport

  1. Label the container properly according to local laboratory protocol

  2. Transport the specimen to the laboratory as soon as possible according to laboratory guidelines

  3. Be familiar with hospital policy recommending the transport of specified pathogens by staff personnel to the laboratory instead of via a pneumatic tube system
• Signs


  Objective and measurable, can be directly observed by a clinician
• Symptoms


  Subjective, felt or experienced by the patient, cannot be clinically confirmed or objectively measured
• Syndrome


  A specific group of signs and symptoms characteristic of a particular disease
• Nomenclature of symptoms


  • cyto- (cell)
  • hepat- (of the liver)
  • -pathy (disease)
  • -emia (of the blood)
  • -itis (inflammation)
  • -lysis (destruction)
  • -oma (tumor)
  • -osis (diseased or abnormal condition)
  • -derma (of the skin)
• The World Health Organization's (WHO) International Classification of Diseases (ICD) is used in clinical fields to classify diseases and monitor morbidity (the number of cases of a disease) and mortality (the number of deaths due to a disease)
• Periods of disease


  1. Incubation period

  2. Prodromal period

  3. Period of illness

  4. Period of decline

  5. Period of convalescence
• Disease progression


  • Infection
  • Latent period
  • Onset of infectiousness
  • Incubation period
  • Onset of symptoms
  • Infectious period
  • End of infectiousness
  • Resolution