Principles of Infectious Disease I Flashcards

1
Q

What are some factors that may be driving the resurgence in infectious diseases?

A
  • POPULATION MOVEMENTS and intrusion of humans and domestic animals into new habitats
  • POPULATION OVERCROWDING, especially coupled with poor public sanitation
  • increased long-distance air TRAVEL - contact/transport of arthropod vectors and primary pathogens
  • MICROBIAL EVOLUTION, leading to natural selection of multi-resistant agents
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2
Q

What are the four major classes of pathogens?

A

-viruses
-bacteria
-fungi
-parasites
Very Bad Funny Parents? Very Blue Faded Pants?

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3
Q

Which of the four agents has a cell wall?

A

Bacteria (with some exceptions) and Fungi

Parasites do not, with some exceptions
Viruses do not

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4
Q

What are the cell plans of the four pathogens?

A
  • viruses: none
  • bacteria: prokaryotic
  • fungi: eukaryotic
  • parasites: eukaryotic
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5
Q

Which of the four pathogens are free living?

A

Bacteria (with some exceptions)
Fungi
Parasites

Not free living: viruses (they are dependent on the host)

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6
Q

Which of the four pathogens are intracellular?

A

Viruses (dependent on the host)

Bacteria, Fungi, and Parasites are not intracellular, with some exceptions.

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7
Q

Describe the general features of viruses

A
  • carry genetic information (nucleic acids; DNA or RNA)
  • have a protein coat (sometimes with a lipid envelope)
  • obligate INTRACELLULAR MICROBES
  • use host cell enzymes and machinery to replicate (make copies of genome and proteins)
  • most common infectious agents in humans
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8
Q

What are the steps of the general replication strategy of viruses?

A

1 - ATTACHEMENT/adsorption to cell (protein on virus binds to receptor on cell surface)

2 - ENTRY/pentration (often involves escape of virus for endocytic vesicle)

3 - UNCOATING (release of nucleic acid into cytoplasm)

4 - REPLICATION (new copies of the genome are made)

5 - TRANSLATION (the genome is transcribed and translated to make virus proteins that are used in producing new virions and to manipulate the host cell, making it more favorable for replication)

6 - VIRUS ASSEMBLY/packaging (a copy of the genome is incorporated into new virions)

7 - RELEASE (may/may not involve lysis of host cell)

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9
Q

Describe the general features of bacteria

A
  • small, single-celled prokaryotic organisms
  • no nucleus, no organelles and typically have a single circular chromosome
  • bound by rigid cell wall
  • divide by binary fission (therefore can multiply rapidly)
  • may be free-living, may live inside host cells - or do both!
  • full metabolic machinery (do not need host); they can perform protein synthesis and have secretory capacity
  • most bacteria are anaerobic, but mostly aerobic bacteria are the ones that infect humans
  • *cell wall can be target of antibiotic treatement
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10
Q

Morphological forms (define)

  • cocci
  • bacilli
  • spiral
  • staph
  • strep
A

Morphological forms (define)

  • cocci: round
  • bacilli: rods
  • spiral
  • staph: grape/cluster
  • strep: chains
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11
Q

What are the main features of the bacterial structure?

A
  • LIPID-BASED MEMBRANE around cytoplasm
  • CELL WALL (composed of peptidoglycan and other molecules) (a few bacteria do not have cell wall - mycoplasma, ureaplasma)
  • with/without CAPSULE/slime layer (thick layer of polysaccharides or proteins surrounding bacteria to protect cell)
  • with/without APPENDAGES (pili-attachment to surfaces and host cells, and other functions; flagella-motility)

some bacteria have an outer lipid membrane (additional?)

**Peptidoglycan is found in Gr+ and Gr-, and is unique to bacteria: some innate immune receptors will respond to these; if we develop drugs that block these enzymes, this wouldn’t be harmful to us because we don’t have peptidoglycan

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12
Q

Gram-positive vs. Gram-negative bacteria

A

Gram-positive:

  • thick cell wall lacking an outer membrane
  • stains purple (thick cell wall retains dye)

Gram-negative:

  • plasma membrane (inner membrane) AND an outer membrane, with a cell wall in between
  • outer membrane is rich in lipopolysaccharide (LPS), also called “endotoxin,” a potent immune stimulant
  • stains light pink
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13
Q

Describe the general features of fungi

A
  • eukaryotic organisms, some are pathogenic for humans
  • cell wall, otherwise very similar to animal cells
  • plasma membrane contains ergosterol (not found in animal cells, it is cholesterol-related, potential therapeutic target for drugs)
  • sizes range from small (like bacteria) to macroscopic (mushrooms)
  • free-living; full metabolic machinery
  • capable of sexual and asexual reproduction
  • no photosynthesis
  • *harder in general to treat because human cells are also eukaryotic
  • *can cause many different types of infections, including deep and systemic infections
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14
Q

Fungal structure

A
  • PLASMA MEMBRANE surrounded by a rigid CELL WALL composed of mannan, chitin, glucan, and other components
  • can be found as YEAST (single cells that reproduce by budding) or MOLD (composed of hyphae: tube-like extensions that branch to create a multi-cellular structure) forms
  • some are dimorphic- exist in yeast or mold form dependent on environment
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15
Q

Describe the general features of parasites

A
  • diverse
  • high prevalence in human populations accounting for significant morbidity and mortality, but with considerable geographic variability
  • two major taxonomic groups: PROTOZOA (microscopic, single-celled eukaryotes) and HELMINTHS (macroscopic, multicellular worms)

-also, ectoparasites: insects like lice, bedbugs, fleas

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16
Q

Protozoa

A
  • eukaryotic
  • often have complex life/infection cycles involving multiple hosts and/or unique environmental reservoirs
  • usually highly adapted to their host(s) (ex: malarial parasite, two hosts mosquito and human)
17
Q

Helminths

A

-worms
-often found in digestive and circulatory systems
may produce eggs or live young
-ex: roundworms, tapeworms, flukes

18
Q

What are four types of atypical pathogens?

A
  • MYCOPLASMA (true bacteria but no cell wall)
  • CHLAMYDIA (bacteria that only replicate in host cells and that lack peptidoglycan in their cell wall)
  • RICKETTSIA (small Gr- bacteria that only replicate in host cells)
  • PRIONS (transmittable protein-mediated diseases; ex: Creutzfeldt-Jakob disease and Mad Cow disease which are progressive neurodegenerative diseases)
19
Q

Characteristics of Prions

A
  • cause spongiform encephalopathies in CNS
  • diseases have long incubation periods (may be inherited or transmissible)
  • prion protein is a cellular protein that can adopt on alternate conformations [the alternate (disease) form catalyzes the conversion of normal forms to the disease form; disease forms of the protein can aggregate in neurons and cause cell death]
20
Q

What is the general immune response to viruses?

A
  • innate immunity includes type-I interferon pathway
  • CD8 T cells eliminate virus-infected cells
  • antibodies neutralize virus in the blood or at mucosal sites
21
Q

What is the general immune response to fungi?

A
  • innate immunity mediated by phagocytes (neutrophils and macrophages)
  • TH1 response key to activating phagocytes so they are better at killing
22
Q

What is the general immune response to bacteria?

A
  • innate mechanisms (complement and phagocytes)
  • antibody response facilitates opsonization and complement functions
  • intracellular bacteria (such as Listeria) require CD8 T cells
23
Q

What is the general immune response to parasites?

A
  • for some agents, the large size presents a challenge (cannot be ingested by phagocytes and processed)
  • TH2 response is critical, mediated by IgE antibodies
  • granules released from eosinophils can be toxic to worms and/or cause a strong inflammatory reponse
24
Q

*Note: CD4 T cells are needed to coordinate most of these responses

A

*Note: CD4 T cells are needed to coordinate most of these responses
(immune responses to viruses, fungi, bacteria, and parasites)