Lecture 3: Pathogenesis Flashcards
Define the two types of viral infections
-abortive vs. permissive
Abortive= virions not produced… why? B/c viruses cannot attach or enter the cell (if they enter, cannot replicate)
Permissive = infectious virions produced
-acute vs. persistent
(Chronic) (latent) (slow) (transforming)
Chronic- HIV
Latent- HSV, VZV
Slow- measles SSPE
Transforming- HPV
persistent viral infections: not completely cleared by the immune
acute viral infections: completely cleared
What is an example of a permissive/persistent (chronic) viral infection ?
HIV
Continuous production and shedding of virions
What is an example for a permissive/persistent (latent) viral infection?
HSV and (VZV) varicella
Virus is still present in the host
Periods of productive infection interspersed with long periods of no virion production
What is an example for a permissive/persistent (slow) viral infection?
Measles, SSPE (subacute sclerosing pancephalities)
-SSPE: years after initial measles infection
Requires a slow accumulation of viral material
What is an example for a permissive/persistent (transforming) viral infection?
HPV (human papilloma virus)
Results in uncontrolled cell growth (inactivates tumors suppressor proteins and impairs cell cycle regulation)
What are some cytopathic effects?
These are visual changes in the host cells due to viral infection (may include cell death)
-histologies changes = inclusion bodies (in nucleus or cytoplasm)
-cell surface changes- syncytia
What type of cytopathic effects involve in the formation of large multi-nucleated cells?
Syncytia
-fusion of infected cell with neighboring cells
-requires viral spike
How do viruses cause cell damage that results in all that cytoplasmic effects?
- By stopping normal cellular processes
- By causing a loss of membrane integrity
What are some ways viruses cause a loss of membrane integrity resulting in cytoplasmic effects?
-allowing an influx of ions (viral mRNA is maintained and can be translated while host mRNA is destroyed)
- insertion of viral glycoproteins in cell membrane (syncytia formation & immunocytopathic effects)
What happens during Non-cytopathic effects?
- Occur with viruses that do not kill the cell & still produce persistent infections
-cells continues to grow and divide - Transformation infection (permissive) (persistent)
Most common point of entry for viruses?
Mucosal surface
Respiratory tract most common point
-GI tract - naked viruses use this route as bile disrupts lipid envelopes
-Conjunctiva
-Urogenital tract
What plays an important role in whether a permissive infection occurs?
Portal of entry (tropism)
Viruses cause different kinds of infections based on the tissue infected (varieties of staph infections depending on its portal of entry)
What are the strategies to evade the immune system?
- Overwhelm the host
- Disarm innate immunity
- Downregulate MHC molecules on cell surface
- Interfere with NK cell activation/function
- Hide
No virus uses just one method of immune evasion
What are immunologically privileged sites?
Eyes
Testes
Ovaries
Brain
-immune mechanisms are reduced in these location
Local spread of a viral infection
Replication in the epithelial cells at, or near, the site of entry.
Syncytia
Common cold, influenza, rotavirus
Generalized infection of a viral spread
From epithelial cells to subepithelial
Enter a lymph node, or blood stream (viremia)
Rapid vehicle for spread to a new niche
Potential secondary viremia
Replication at remote sites
-specific issue beyond point of entry (hepatitis A)
-multiple tissues beyond point of entry= systemic infection (measles)
Viral spread of HSV
Through peripheral nerves
-trigeminal nerve (site of viral latency)
What are the viruses, bacteria, and parasites (TERATOGENS) that can cross the placenta and harm the fetus? VERTICAL TRANSMISSION
TORCH infections
T- toxoplasmosis (a parasite)
O- VZV, Zika, parvovirus B19, syphills, others
R- rubella
C - cytomegalovirus
H- herpes simplex virus
When do clinical symptoms become apparent? What are some examples of immune responses?
-When enough cells are damaged or killed.
-edema (Swelling), inflammation (may be harmful (HCV) or helpful)
Shedding
-localized vs. generalized
Release of new virions back into the environment
-shedding occurs from the same location = localized (influenza infects URT, sheds URT)
-shedding occurs from a location other than the infected site = generalized (poliovirus enters mouth, sheds through feces)
once shed, the virus can go to infect others
When does shedding occur for localized infections
Shedding occurs from the same location as the infection site
(Influenza infects URT and virions are spread from the URT via coughing)
When does shedding occur for generalized infections
Shedding occurs from a location other than the infection site
(Poliovirus enters through the mouth, but is shed through feces)
Once shed, the virus can go to infect others
Infectiousness- the R0 value
How many new infections arise from a single infected individual
R0 of 2 = that each infected patient will infect 2 others on average
R0 of 18 = each infected patient will infect 18 others on average
how many people can one person infect
R0 value can be used for
Can be used to calculate the % of the population that needs to be immune to achieve herd immunity
100*(1-1R0)
% required of population needs to be immune for herd immunity for SARS-CoV with R0=3
Use formula
100(1-1/R0)
100(1-1/3)
=67% of the population needs to be immune for herd immunity
