Lecture 9: Infectious Diseases I Flashcards
Commensal microbes
Part of normal flora; agents of endogenous function when homeostasis is disrupted
Environmental microbes
Originate externally; agents of exogenous colonization/infection
Obligate pathogens
Capable of causing clinical disease despite host immune defenses e.g. Bacillus anthracis, influenza
Opportunistic pathogens
Relies on alteration of host immunity for infection e.g. Staph. spp, Candida spp yeast
How does microbiome disruption affect us?
Normal flora alteration enables symptomatic overgrowth of commensals, endogenous disseminated infection, or exogenous pathogen invasion
Risk factors that could alter our microbiome
- Antimicrobials
- Mucosal pH changes
- Burns, trauma
- Surgery
- Immune deficiency
C. diff infection
Antibiotic-assoc. disruption of GI microbiome enables opportunistic toxigenic strains to colonize
Endemic
Disease steady state in a population
Outbreak
Case numbers exceed usual expectation for a defined community/region/season
Epidemic
Disease spreads rapidly and deaths > steady state
Pandemic
Global epidemic
Bioterrorism
Use of infectious agents as weapons
What makes a good bioterrorism agent?
- Easy dissemination
- High mortality
- Lack of effective therapies
Viruses
- Obligate intracellular
- Less than 1 um
- Nucleic acid core encapsulated by protein capsid
- ss or ds RNA/DNA genome
- Enveloped and non-enveloped
Why is influenza so infectious?
- Segmented RNA genome
- Multiple zoonotic reservoirs
- Easy transmission
- Antigenic shift
Influenza features
- Enveloped, ssRNA
- Segmented
- A, B, C types
- H/N subtypes (hemagglutinin/neuraminidase)
Prions
- Cause abnormal PrP protein folding in brain
- Cause transmissible spongiform encephalopathies
- Protease-resistant accumulations -> rapid neuron degeneration
Bacteria
- Prokaryotes w/ cell membrane + wall
- No membrane-bound nuclei/organelles
- Most require a host for nutrition, synthesize own nucleic acids
- IC/EC, aerobic/anaerobic, motile/nonmotile
- Gram + peptidoglycan cell wall or Gram - LPS cell wall
Fungi
- Eukaryotes w/ cell membrane + wall
- Yeasts or moulds
- Infection by inhalation/trauma/contact with spores
Yeast
- Single celled fungi
- Form smooth, creamy colonies
- Propagate by asexual budding
Moulds
- Multicellular fungi
- Form hyphae (elongated cells); “fuzzy”/”powdery”
Protazoans
- Single celled parasites
e.g. Plasmodium vivax, Giardia intestinalis
Helminths
- Multicellular parasites
1. Roundworms (nematodes)
2. Flatworms (cestodes)
3. Flukes (trematodes)
e.g. SubQ or lymphatic filariasis
