Principles of Infectious Disease I Flashcards
What are some factors that may be driving the resurgence in infectious diseases?
- 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
What are the four major classes of pathogens?
-viruses
-bacteria
-fungi
-parasites
Very Bad Funny Parents? Very Blue Faded Pants?
Which of the four agents has a cell wall?
Bacteria (with some exceptions) and Fungi
Parasites do not, with some exceptions
Viruses do not
What are the cell plans of the four pathogens?
- viruses: none
- bacteria: prokaryotic
- fungi: eukaryotic
- parasites: eukaryotic
Which of the four pathogens are free living?
Bacteria (with some exceptions)
Fungi
Parasites
Not free living: viruses (they are dependent on the host)
Which of the four pathogens are intracellular?
Viruses (dependent on the host)
Bacteria, Fungi, and Parasites are not intracellular, with some exceptions.
Describe the general features of viruses
- 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
What are the steps of the general replication strategy of viruses?
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)
Describe the general features of bacteria
- 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
Morphological forms (define)
- cocci
- bacilli
- spiral
- staph
- strep
Morphological forms (define)
- cocci: round
- bacilli: rods
- spiral
- staph: grape/cluster
- strep: chains
What are the main features of the bacterial structure?
- 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
Gram-positive vs. Gram-negative bacteria
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
Describe the general features of fungi
- 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
Fungal structure
- 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
Describe the general features of parasites
- 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
Protozoa
- 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)
Helminths
-worms
-often found in digestive and circulatory systems
may produce eggs or live young
-ex: roundworms, tapeworms, flukes
What are four types of atypical pathogens?
- 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)
Characteristics of Prions
- 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]
What is the general immune response to viruses?
- innate immunity includes type-I interferon pathway
- CD8 T cells eliminate virus-infected cells
- antibodies neutralize virus in the blood or at mucosal sites
What is the general immune response to fungi?
- innate immunity mediated by phagocytes (neutrophils and macrophages)
- TH1 response key to activating phagocytes so they are better at killing
What is the general immune response to bacteria?
- innate mechanisms (complement and phagocytes)
- antibody response facilitates opsonization and complement functions
- intracellular bacteria (such as Listeria) require CD8 T cells
What is the general immune response to parasites?
- 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
*Note: CD4 T cells are needed to coordinate most of these responses
*Note: CD4 T cells are needed to coordinate most of these responses
(immune responses to viruses, fungi, bacteria, and parasites)
