transmission and colonisation

• What increases the chance of pathogen transmission?

  The more organisms shed
• What factors affect the stability of pathogens?

  Species and stress conditions
• Which pathogen is highly resistant to desiccation?

  Mycobacterium tuberculosis
• What type of pathogens rely on direct transmission?

  Less environmentally resistant pathogens
• What does the infectious dose depend on?

  Species, site of infection, and host status
• What is the infectious dose for Bacillus anthracis?

  8000 – 80000 spores
• How many cells are needed for Salmonella enteritidis infection?

  1,000,000 cells
• What is the infectious dose for Shigella dysenteriae?

  10 cells
• How many cells are needed for Coxiella burnettii infection?

  1 cell
• What is the infectious dose for Francisella tularensis?

  Less than 1 cell
• Why is infection via the respiratory tract more acute?

  It depends on nutrition, genetics, and age
• What must a pathogen do to colonize a new host?

  Enter, attach, and evade host defenses
• What are common portals of entry for pathogens?

  Mucous membranes, broken skin, glands
• How does the skin act as a barrier to infection?

  Normal flora, dryness, and low pH
• What can cause entry through the skin?

  Cuts, abrasions, bites, puncture wounds
• Why are burns particularly prone to infection?

  They compromise the skin barrier
• How many skin scales can be shed per day?

  10$^8$ scales/day
• How many viable organisms are inhaled daily through the respiratory tract?

  Approximately 10,000 viable organisms
• What removes inhaled organisms from the respiratory tract?

  Entrapment in mucous and swallowing
• What aids in the clearance of inhaled particles in the deep lung?

  Alveolar macrophages
• What must a pathogen do to colonize the respiratory tract?

  Adhere strongly and resist clearance mechanisms
• What pathogen is known to resist macrophage killing?

  Mycobacterium tuberculosis
• How do respiratory pathogens damage the respiratory tract?

  By causing mucous production, sneezing, and coughing
• What is a consequence of microbial growth in food?

  Food poisoning
• What is required for colonization in the gastrointestinal tract?

  Ingestion of large amounts of organisms
• What pathogen is associated with canned foods?

  Clostridium botulinum
• What pathogen is associated with rice?

  Bacillus cereus
• What pathogens are associated with badly stored nuts and pulses?

  Aspergilli
• How does transmission from the GI tract occur?

  In unsanitary conditions via faecal-oral spread
• What reduces the incidence of waterborne diseases in the first world?

  Water treatment, sanitation, and purification
• What are the two main types of urinary tract infections?

  UTIs and STDs
• How do pathogens adapt to aid in attachment in the urinary tract?

  By possessing adhesins that bind to epithelial cells
• What is the most common cause of UTIs in the UK?

  Escherichia coli
• Why are pathogens causing STDs poorly transmitted?

  They have low environmental resistance and persistence
• How do pathogens causing STDs and UTIs transmit?

  Through direct forms of transmission
• What are common vehicles for bloodborne pathogens?

  Needles, contaminated blood products, and surgery
• How can pathogens enter and exit a host through the blood?

  By parenteral routes and breaks in skin
• What is transplacental transmission?

  Transmission from mother to baby
• What are the main mechanisms of pathogen transmission?

  Contact, disease vehicles, and vectors
• What influences the effectiveness of human-to-human transmission?

  Number of organisms shed and environmental stability