Lecture 7: Infectious Diseases Flashcards
What causes infection
bacteria, viruses, fungi, protozoa, prions
what are the steps of infection
Chronologic sequence of events
Portal of entry
Regulated by virulence factors
are most infectious agents targeting specific cells or organs
yes
How does the infectious agent get into the body
Mucosae (respiratory, alimentary, lower urinary, reproductive, ear/eye)
Subcutaneous tissues
what are the bodies cells that help to stop infectious agents initial multiplication
Macrophage, lymphocytes, dendritic cells
where does the infectious agent go after initial multiplication
Then local (submucosa, subcutis), regional (lymph node), systemic spread
what does the mucus protective layer of the body do
Prevents direct adherence
Blocks/traps organisms
Can facilitate action of phagocytes
Delivers antigens to local lymphoid tissue
Keeps antimicrobial substances and atb close to mucosa
what can cause changes in goblet cell function and chemical composition of mucus that can lower protection
Dehydration Shipping Humidity Ventilation Weather changes
how have microorganisms evolved to take advantage of our mucus protective layer
Source of food (carbohydrates, peptides)
If able to colonize inner mucus: prevents expulsion
Can specifically adhere to molecules in mucus
Microbial mucolysis ability is virulence factor
how do you ingest an infectious agent
via infectious fomites
where is the thickest layer of mucus protective layer
in the colon
where is the thinnest layer of the mucus protective layer
in the jejunum
what is located in the protective mucosal fluids
gastric acid, lyzozymes
describe inhaling a fomite
Nostrils Nasal turbinates, pharynx or lower airways
Depends on size, shape, weight
Virus > prions > bacteria > fungi > Protozoa
BUT mostly inhaled with fomites!
Air turbulence in turbinates increases deposition
describe the mucuciliary apparatus
Biphasic mucus layer Tip of cilia in gel Nasal cavity & sinus: Moves downward Conductive respiratory: Moves upward Ultimately swallowed Injury to epithelial cells (influenza, rhino) can disrupt and cause secondary bacterial infections
describe infectious agent cutaneous penetration
Via abrasions, scratches, bite wounds, insect bite
Limited range of host targets
but limited defenses
describe the pathogenicity of the infectious agents
Regulated by virulence factors In bacterial genes Their expression permits bacteria to Colonize mucosae, Infect cells, Grow and replicate, Cause cell death
what infectious agents have good motility
spirochetes
what infectious agents can digest the mucus layer
clostridium
describe colonization of an infectious agent
Adhesion of sufficient amount of bacteria Via: Fimbria/Pilus Adhesion molecules Needs to be faster than cell renewal
describe spreading of an infectious agent
Spreading
Destruction of collagen, tight junctions between cells
Provides safe spot for bacteria
describe the toxins released by infectious agents
Exotoxins (gram +), endotoxins (gram -) (LPS: lipopolysaccharide)
Damages cells and extra-cellular matrix
Kills cells via cytolysis or activation of complement
since Viruses are unable to produce energy and contain a limited number of enzymes what are they considered
obligate intracellular parasites
how have viruses evolved
Have evolved to target specific cells in animals to sustain theirs needs
Not as many virulence factor
not as complex as bacteria.
describe permissive viral target cells
Allows for viral replication
describe non permissive viral target cells
no replication – used as reservoir
Can become permissive (ex with cell maturation or activation)
describe step 1 of the viral replication cycle
- Attachement and Entry
Determines which organs are infected
Viruses bind to normally expressed receptors
describe step 2 of the viral replication cycle
- Replication stage
How much of the cell is hijacked
Organelles, genome, other
How much cell dysfunction, cell death
describe step 3 of the viral replication cycle
- Shedding
How the virus exits determines cell’s fate
If cell killed or lysed causes more severe disease
describe parvovirus viral replication
Infects intestinal crypt epithelial cells
Receptors on basolateral surface
So coming in from circulation, not directly from intestine
M-cell Peyer’s patch circulation
Not most direct; prevents contact with protective mechanism, tight junctions
how do non-enveloped viruses attach to cells
They attach to host cells using a protein coat
(viral coat, capsid, capsomeres)
Usually kill infected cells to release newly formed virus.
how do enveloped viruses attach to cells
They attach to host cells using a viral envelope
Usually do not kill infected cells to release newly formed virus.
what are the innate host cell defences against viruses
Inflammation
Interferon
what are the host cell mediated immunity against viruses
NK and cytotoxic T cells
Antibodies important only for subsequent infections
